This is libc.info, produced by makeinfo version 6.5 from libc.texinfo.

This is ‘The GNU C Library Reference Manual’, for version 2.33 (GNU).

   Copyright © 1993–2021 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “Free Software Needs Free Documentation” and
“GNU Lesser General Public License”, the Front-Cover texts being “A GNU
Manual”, and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License".

   (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.”
INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU C library functions and macros
START-INFO-DIR-ENTRY
* ALTWERASE: (libc)Local Modes.
* ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions.
* ARG_MAX: (libc)General Limits.
* BC_BASE_MAX: (libc)Utility Limits.
* BC_DIM_MAX: (libc)Utility Limits.
* BC_SCALE_MAX: (libc)Utility Limits.
* BC_STRING_MAX: (libc)Utility Limits.
* BRKINT: (libc)Input Modes.
* BUFSIZ: (libc)Controlling Buffering.
* CCTS_OFLOW: (libc)Control Modes.
* CHAR_BIT: (libc)Width of Type.
* CHILD_MAX: (libc)General Limits.
* CIGNORE: (libc)Control Modes.
* CLK_TCK: (libc)Processor Time.
* CLOCAL: (libc)Control Modes.
* CLOCKS_PER_SEC: (libc)CPU Time.
* CLOCK_MONOTONIC: (libc)Getting the Time.
* CLOCK_REALTIME: (libc)Getting the Time.
* COLL_WEIGHTS_MAX: (libc)Utility Limits.
* CPU_CLR: (libc)CPU Affinity.
* CPU_FEATURE_USABLE: (libc)X86.
* CPU_ISSET: (libc)CPU Affinity.
* CPU_SET: (libc)CPU Affinity.
* CPU_SETSIZE: (libc)CPU Affinity.
* CPU_ZERO: (libc)CPU Affinity.
* CREAD: (libc)Control Modes.
* CRTS_IFLOW: (libc)Control Modes.
* CS5: (libc)Control Modes.
* CS6: (libc)Control Modes.
* CS7: (libc)Control Modes.
* CS8: (libc)Control Modes.
* CSIZE: (libc)Control Modes.
* CSTOPB: (libc)Control Modes.
* DTTOIF: (libc)Directory Entries.
* E2BIG: (libc)Error Codes.
* EACCES: (libc)Error Codes.
* EADDRINUSE: (libc)Error Codes.
* EADDRNOTAVAIL: (libc)Error Codes.
* EADV: (libc)Error Codes.
* EAFNOSUPPORT: (libc)Error Codes.
* EAGAIN: (libc)Error Codes.
* EALREADY: (libc)Error Codes.
* EAUTH: (libc)Error Codes.
* EBACKGROUND: (libc)Error Codes.
* EBADE: (libc)Error Codes.
* EBADF: (libc)Error Codes.
* EBADFD: (libc)Error Codes.
* EBADMSG: (libc)Error Codes.
* EBADR: (libc)Error Codes.
* EBADRPC: (libc)Error Codes.
* EBADRQC: (libc)Error Codes.
* EBADSLT: (libc)Error Codes.
* EBFONT: (libc)Error Codes.
* EBUSY: (libc)Error Codes.
* ECANCELED: (libc)Error Codes.
* ECHILD: (libc)Error Codes.
* ECHO: (libc)Local Modes.
* ECHOCTL: (libc)Local Modes.
* ECHOE: (libc)Local Modes.
* ECHOK: (libc)Local Modes.
* ECHOKE: (libc)Local Modes.
* ECHONL: (libc)Local Modes.
* ECHOPRT: (libc)Local Modes.
* ECHRNG: (libc)Error Codes.
* ECOMM: (libc)Error Codes.
* ECONNABORTED: (libc)Error Codes.
* ECONNREFUSED: (libc)Error Codes.
* ECONNRESET: (libc)Error Codes.
* ED: (libc)Error Codes.
* EDEADLK: (libc)Error Codes.
* EDEADLOCK: (libc)Error Codes.
* EDESTADDRREQ: (libc)Error Codes.
* EDIED: (libc)Error Codes.
* EDOM: (libc)Error Codes.
* EDOTDOT: (libc)Error Codes.
* EDQUOT: (libc)Error Codes.
* EEXIST: (libc)Error Codes.
* EFAULT: (libc)Error Codes.
* EFBIG: (libc)Error Codes.
* EFTYPE: (libc)Error Codes.
* EGRATUITOUS: (libc)Error Codes.
* EGREGIOUS: (libc)Error Codes.
* EHOSTDOWN: (libc)Error Codes.
* EHOSTUNREACH: (libc)Error Codes.
* EHWPOISON: (libc)Error Codes.
* EIDRM: (libc)Error Codes.
* EIEIO: (libc)Error Codes.
* EILSEQ: (libc)Error Codes.
* EINPROGRESS: (libc)Error Codes.
* EINTR: (libc)Error Codes.
* EINVAL: (libc)Error Codes.
* EIO: (libc)Error Codes.
* EISCONN: (libc)Error Codes.
* EISDIR: (libc)Error Codes.
* EISNAM: (libc)Error Codes.
* EKEYEXPIRED: (libc)Error Codes.
* EKEYREJECTED: (libc)Error Codes.
* EKEYREVOKED: (libc)Error Codes.
* EL2HLT: (libc)Error Codes.
* EL2NSYNC: (libc)Error Codes.
* EL3HLT: (libc)Error Codes.
* EL3RST: (libc)Error Codes.
* ELIBACC: (libc)Error Codes.
* ELIBBAD: (libc)Error Codes.
* ELIBEXEC: (libc)Error Codes.
* ELIBMAX: (libc)Error Codes.
* ELIBSCN: (libc)Error Codes.
* ELNRNG: (libc)Error Codes.
* ELOOP: (libc)Error Codes.
* EMEDIUMTYPE: (libc)Error Codes.
* EMFILE: (libc)Error Codes.
* EMLINK: (libc)Error Codes.
* EMSGSIZE: (libc)Error Codes.
* EMULTIHOP: (libc)Error Codes.
* ENAMETOOLONG: (libc)Error Codes.
* ENAVAIL: (libc)Error Codes.
* ENEEDAUTH: (libc)Error Codes.
* ENETDOWN: (libc)Error Codes.
* ENETRESET: (libc)Error Codes.
* ENETUNREACH: (libc)Error Codes.
* ENFILE: (libc)Error Codes.
* ENOANO: (libc)Error Codes.
* ENOBUFS: (libc)Error Codes.
* ENOCSI: (libc)Error Codes.
* ENODATA: (libc)Error Codes.
* ENODEV: (libc)Error Codes.
* ENOENT: (libc)Error Codes.
* ENOEXEC: (libc)Error Codes.
* ENOKEY: (libc)Error Codes.
* ENOLCK: (libc)Error Codes.
* ENOLINK: (libc)Error Codes.
* ENOMEDIUM: (libc)Error Codes.
* ENOMEM: (libc)Error Codes.
* ENOMSG: (libc)Error Codes.
* ENONET: (libc)Error Codes.
* ENOPKG: (libc)Error Codes.
* ENOPROTOOPT: (libc)Error Codes.
* ENOSPC: (libc)Error Codes.
* ENOSR: (libc)Error Codes.
* ENOSTR: (libc)Error Codes.
* ENOSYS: (libc)Error Codes.
* ENOTBLK: (libc)Error Codes.
* ENOTCONN: (libc)Error Codes.
* ENOTDIR: (libc)Error Codes.
* ENOTEMPTY: (libc)Error Codes.
* ENOTNAM: (libc)Error Codes.
* ENOTRECOVERABLE: (libc)Error Codes.
* ENOTSOCK: (libc)Error Codes.
* ENOTSUP: (libc)Error Codes.
* ENOTTY: (libc)Error Codes.
* ENOTUNIQ: (libc)Error Codes.
* ENXIO: (libc)Error Codes.
* EOF: (libc)EOF and Errors.
* EOPNOTSUPP: (libc)Error Codes.
* EOVERFLOW: (libc)Error Codes.
* EOWNERDEAD: (libc)Error Codes.
* EPERM: (libc)Error Codes.
* EPFNOSUPPORT: (libc)Error Codes.
* EPIPE: (libc)Error Codes.
* EPROCLIM: (libc)Error Codes.
* EPROCUNAVAIL: (libc)Error Codes.
* EPROGMISMATCH: (libc)Error Codes.
* EPROGUNAVAIL: (libc)Error Codes.
* EPROTO: (libc)Error Codes.
* EPROTONOSUPPORT: (libc)Error Codes.
* EPROTOTYPE: (libc)Error Codes.
* EQUIV_CLASS_MAX: (libc)Utility Limits.
* ERANGE: (libc)Error Codes.
* EREMCHG: (libc)Error Codes.
* EREMOTE: (libc)Error Codes.
* EREMOTEIO: (libc)Error Codes.
* ERESTART: (libc)Error Codes.
* ERFKILL: (libc)Error Codes.
* EROFS: (libc)Error Codes.
* ERPCMISMATCH: (libc)Error Codes.
* ESHUTDOWN: (libc)Error Codes.
* ESOCKTNOSUPPORT: (libc)Error Codes.
* ESPIPE: (libc)Error Codes.
* ESRCH: (libc)Error Codes.
* ESRMNT: (libc)Error Codes.
* ESTALE: (libc)Error Codes.
* ESTRPIPE: (libc)Error Codes.
* ETIME: (libc)Error Codes.
* ETIMEDOUT: (libc)Error Codes.
* ETOOMANYREFS: (libc)Error Codes.
* ETXTBSY: (libc)Error Codes.
* EUCLEAN: (libc)Error Codes.
* EUNATCH: (libc)Error Codes.
* EUSERS: (libc)Error Codes.
* EWOULDBLOCK: (libc)Error Codes.
* EXDEV: (libc)Error Codes.
* EXFULL: (libc)Error Codes.
* EXIT_FAILURE: (libc)Exit Status.
* EXIT_SUCCESS: (libc)Exit Status.
* EXPR_NEST_MAX: (libc)Utility Limits.
* FD_CLOEXEC: (libc)Descriptor Flags.
* FD_CLR: (libc)Waiting for I/O.
* FD_ISSET: (libc)Waiting for I/O.
* FD_SET: (libc)Waiting for I/O.
* FD_SETSIZE: (libc)Waiting for I/O.
* FD_ZERO: (libc)Waiting for I/O.
* FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN.
* FILENAME_MAX: (libc)Limits for Files.
* FLUSHO: (libc)Local Modes.
* FOPEN_MAX: (libc)Opening Streams.
* FP_ILOGB0: (libc)Exponents and Logarithms.
* FP_ILOGBNAN: (libc)Exponents and Logarithms.
* FP_LLOGB0: (libc)Exponents and Logarithms.
* FP_LLOGBNAN: (libc)Exponents and Logarithms.
* F_DUPFD: (libc)Duplicating Descriptors.
* F_GETFD: (libc)Descriptor Flags.
* F_GETFL: (libc)Getting File Status Flags.
* F_GETLK: (libc)File Locks.
* F_GETOWN: (libc)Interrupt Input.
* F_OFD_GETLK: (libc)Open File Description Locks.
* F_OFD_SETLK: (libc)Open File Description Locks.
* F_OFD_SETLKW: (libc)Open File Description Locks.
* F_OK: (libc)Testing File Access.
* F_SETFD: (libc)Descriptor Flags.
* F_SETFL: (libc)Getting File Status Flags.
* F_SETLK: (libc)File Locks.
* F_SETLKW: (libc)File Locks.
* F_SETOWN: (libc)Interrupt Input.
* HAS_CPU_FEATURE: (libc)X86.
* HUGE_VAL: (libc)Math Error Reporting.
* HUGE_VALF: (libc)Math Error Reporting.
* HUGE_VALL: (libc)Math Error Reporting.
* HUGE_VAL_FN: (libc)Math Error Reporting.
* HUGE_VAL_FNx: (libc)Math Error Reporting.
* HUPCL: (libc)Control Modes.
* I: (libc)Complex Numbers.
* ICANON: (libc)Local Modes.
* ICRNL: (libc)Input Modes.
* IEXTEN: (libc)Local Modes.
* IFNAMSIZ: (libc)Interface Naming.
* IFTODT: (libc)Directory Entries.
* IGNBRK: (libc)Input Modes.
* IGNCR: (libc)Input Modes.
* IGNPAR: (libc)Input Modes.
* IMAXBEL: (libc)Input Modes.
* INADDR_ANY: (libc)Host Address Data Type.
* INADDR_BROADCAST: (libc)Host Address Data Type.
* INADDR_LOOPBACK: (libc)Host Address Data Type.
* INADDR_NONE: (libc)Host Address Data Type.
* INFINITY: (libc)Infinity and NaN.
* INLCR: (libc)Input Modes.
* INPCK: (libc)Input Modes.
* IPPORT_RESERVED: (libc)Ports.
* IPPORT_USERRESERVED: (libc)Ports.
* ISIG: (libc)Local Modes.
* ISTRIP: (libc)Input Modes.
* IXANY: (libc)Input Modes.
* IXOFF: (libc)Input Modes.
* IXON: (libc)Input Modes.
* LINE_MAX: (libc)Utility Limits.
* LINK_MAX: (libc)Limits for Files.
* L_ctermid: (libc)Identifying the Terminal.
* L_cuserid: (libc)Who Logged In.
* L_tmpnam: (libc)Temporary Files.
* MAXNAMLEN: (libc)Limits for Files.
* MAXSYMLINKS: (libc)Symbolic Links.
* MAX_CANON: (libc)Limits for Files.
* MAX_INPUT: (libc)Limits for Files.
* MB_CUR_MAX: (libc)Selecting the Conversion.
* MB_LEN_MAX: (libc)Selecting the Conversion.
* MDMBUF: (libc)Control Modes.
* MSG_DONTROUTE: (libc)Socket Data Options.
* MSG_OOB: (libc)Socket Data Options.
* MSG_PEEK: (libc)Socket Data Options.
* NAME_MAX: (libc)Limits for Files.
* NAN: (libc)Infinity and NaN.
* NCCS: (libc)Mode Data Types.
* NGROUPS_MAX: (libc)General Limits.
* NOFLSH: (libc)Local Modes.
* NOKERNINFO: (libc)Local Modes.
* NSIG: (libc)Standard Signals.
* NULL: (libc)Null Pointer Constant.
* ONLCR: (libc)Output Modes.
* ONOEOT: (libc)Output Modes.
* OPEN_MAX: (libc)General Limits.
* OPOST: (libc)Output Modes.
* OXTABS: (libc)Output Modes.
* O_ACCMODE: (libc)Access Modes.
* O_APPEND: (libc)Operating Modes.
* O_ASYNC: (libc)Operating Modes.
* O_CREAT: (libc)Open-time Flags.
* O_DIRECTORY: (libc)Open-time Flags.
* O_EXCL: (libc)Open-time Flags.
* O_EXEC: (libc)Access Modes.
* O_EXLOCK: (libc)Open-time Flags.
* O_FSYNC: (libc)Operating Modes.
* O_IGNORE_CTTY: (libc)Open-time Flags.
* O_NDELAY: (libc)Operating Modes.
* O_NOATIME: (libc)Operating Modes.
* O_NOCTTY: (libc)Open-time Flags.
* O_NOFOLLOW: (libc)Open-time Flags.
* O_NOLINK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Operating Modes.
* O_NOTRANS: (libc)Open-time Flags.
* O_PATH: (libc)Access Modes.
* O_RDONLY: (libc)Access Modes.
* O_RDWR: (libc)Access Modes.
* O_READ: (libc)Access Modes.
* O_SHLOCK: (libc)Open-time Flags.
* O_SYNC: (libc)Operating Modes.
* O_TMPFILE: (libc)Open-time Flags.
* O_TRUNC: (libc)Open-time Flags.
* O_WRITE: (libc)Access Modes.
* O_WRONLY: (libc)Access Modes.
* PARENB: (libc)Control Modes.
* PARMRK: (libc)Input Modes.
* PARODD: (libc)Control Modes.
* PATH_MAX: (libc)Limits for Files.
* PA_FLAG_MASK: (libc)Parsing a Template String.
* PENDIN: (libc)Local Modes.
* PF_FILE: (libc)Local Namespace Details.
* PF_INET6: (libc)Internet Namespace.
* PF_INET: (libc)Internet Namespace.
* PF_LOCAL: (libc)Local Namespace Details.
* PF_UNIX: (libc)Local Namespace Details.
* PIPE_BUF: (libc)Limits for Files.
* PTHREAD_ATTR_NO_SIGMASK_NP: (libc)Initial Thread Signal Mask.
* P_tmpdir: (libc)Temporary Files.
* RAND_MAX: (libc)ISO Random.
* RE_DUP_MAX: (libc)General Limits.
* RLIM_INFINITY: (libc)Limits on Resources.
* R_OK: (libc)Testing File Access.
* SA_NOCLDSTOP: (libc)Flags for Sigaction.
* SA_ONSTACK: (libc)Flags for Sigaction.
* SA_RESTART: (libc)Flags for Sigaction.
* SEEK_CUR: (libc)File Positioning.
* SEEK_END: (libc)File Positioning.
* SEEK_SET: (libc)File Positioning.
* SIGABRT: (libc)Program Error Signals.
* SIGALRM: (libc)Alarm Signals.
* SIGBUS: (libc)Program Error Signals.
* SIGCHLD: (libc)Job Control Signals.
* SIGCLD: (libc)Job Control Signals.
* SIGCONT: (libc)Job Control Signals.
* SIGEMT: (libc)Program Error Signals.
* SIGFPE: (libc)Program Error Signals.
* SIGHUP: (libc)Termination Signals.
* SIGILL: (libc)Program Error Signals.
* SIGINFO: (libc)Miscellaneous Signals.
* SIGINT: (libc)Termination Signals.
* SIGIO: (libc)Asynchronous I/O Signals.
* SIGIOT: (libc)Program Error Signals.
* SIGKILL: (libc)Termination Signals.
* SIGLOST: (libc)Operation Error Signals.
* SIGPIPE: (libc)Operation Error Signals.
* SIGPOLL: (libc)Asynchronous I/O Signals.
* SIGPROF: (libc)Alarm Signals.
* SIGQUIT: (libc)Termination Signals.
* SIGSEGV: (libc)Program Error Signals.
* SIGSTOP: (libc)Job Control Signals.
* SIGSYS: (libc)Program Error Signals.
* SIGTERM: (libc)Termination Signals.
* SIGTRAP: (libc)Program Error Signals.
* SIGTSTP: (libc)Job Control Signals.
* SIGTTIN: (libc)Job Control Signals.
* SIGTTOU: (libc)Job Control Signals.
* SIGURG: (libc)Asynchronous I/O Signals.
* SIGUSR1: (libc)Miscellaneous Signals.
* SIGUSR2: (libc)Miscellaneous Signals.
* SIGVTALRM: (libc)Alarm Signals.
* SIGWINCH: (libc)Miscellaneous Signals.
* SIGXCPU: (libc)Operation Error Signals.
* SIGXFSZ: (libc)Operation Error Signals.
* SIG_ERR: (libc)Basic Signal Handling.
* SNAN: (libc)Infinity and NaN.
* SNANF: (libc)Infinity and NaN.
* SNANFN: (libc)Infinity and NaN.
* SNANFNx: (libc)Infinity and NaN.
* SNANL: (libc)Infinity and NaN.
* SOCK_DGRAM: (libc)Communication Styles.
* SOCK_RAW: (libc)Communication Styles.
* SOCK_RDM: (libc)Communication Styles.
* SOCK_SEQPACKET: (libc)Communication Styles.
* SOCK_STREAM: (libc)Communication Styles.
* SOL_SOCKET: (libc)Socket-Level Options.
* SSIZE_MAX: (libc)General Limits.
* STREAM_MAX: (libc)General Limits.
* SUN_LEN: (libc)Local Namespace Details.
* S_IFMT: (libc)Testing File Type.
* S_ISBLK: (libc)Testing File Type.
* S_ISCHR: (libc)Testing File Type.
* S_ISDIR: (libc)Testing File Type.
* S_ISFIFO: (libc)Testing File Type.
* S_ISLNK: (libc)Testing File Type.
* S_ISREG: (libc)Testing File Type.
* S_ISSOCK: (libc)Testing File Type.
* S_TYPEISMQ: (libc)Testing File Type.
* S_TYPEISSEM: (libc)Testing File Type.
* S_TYPEISSHM: (libc)Testing File Type.
* TMP_MAX: (libc)Temporary Files.
* TOSTOP: (libc)Local Modes.
* TZNAME_MAX: (libc)General Limits.
* VDISCARD: (libc)Other Special.
* VDSUSP: (libc)Signal Characters.
* VEOF: (libc)Editing Characters.
* VEOL2: (libc)Editing Characters.
* VEOL: (libc)Editing Characters.
* VERASE: (libc)Editing Characters.
* VINTR: (libc)Signal Characters.
* VKILL: (libc)Editing Characters.
* VLNEXT: (libc)Other Special.
* VMIN: (libc)Noncanonical Input.
* VQUIT: (libc)Signal Characters.
* VREPRINT: (libc)Editing Characters.
* VSTART: (libc)Start/Stop Characters.
* VSTATUS: (libc)Other Special.
* VSTOP: (libc)Start/Stop Characters.
* VSUSP: (libc)Signal Characters.
* VTIME: (libc)Noncanonical Input.
* VWERASE: (libc)Editing Characters.
* WCHAR_MAX: (libc)Extended Char Intro.
* WCHAR_MIN: (libc)Extended Char Intro.
* WCOREDUMP: (libc)Process Completion Status.
* WEOF: (libc)EOF and Errors.
* WEOF: (libc)Extended Char Intro.
* WEXITSTATUS: (libc)Process Completion Status.
* WIFEXITED: (libc)Process Completion Status.
* WIFSIGNALED: (libc)Process Completion Status.
* WIFSTOPPED: (libc)Process Completion Status.
* WSTOPSIG: (libc)Process Completion Status.
* WTERMSIG: (libc)Process Completion Status.
* W_OK: (libc)Testing File Access.
* X_OK: (libc)Testing File Access.
* _Complex_I: (libc)Complex Numbers.
* _Exit: (libc)Termination Internals.
* _IOFBF: (libc)Controlling Buffering.
* _IOLBF: (libc)Controlling Buffering.
* _IONBF: (libc)Controlling Buffering.
* _Imaginary_I: (libc)Complex Numbers.
* _PATH_UTMP: (libc)Manipulating the Database.
* _PATH_WTMP: (libc)Manipulating the Database.
* _POSIX2_C_DEV: (libc)System Options.
* _POSIX2_C_VERSION: (libc)Version Supported.
* _POSIX2_FORT_DEV: (libc)System Options.
* _POSIX2_FORT_RUN: (libc)System Options.
* _POSIX2_LOCALEDEF: (libc)System Options.
* _POSIX2_SW_DEV: (libc)System Options.
* _POSIX_CHOWN_RESTRICTED: (libc)Options for Files.
* _POSIX_JOB_CONTROL: (libc)System Options.
* _POSIX_NO_TRUNC: (libc)Options for Files.
* _POSIX_SAVED_IDS: (libc)System Options.
* _POSIX_VDISABLE: (libc)Options for Files.
* _POSIX_VERSION: (libc)Version Supported.
* __fbufsize: (libc)Controlling Buffering.
* __flbf: (libc)Controlling Buffering.
* __fpending: (libc)Controlling Buffering.
* __fpurge: (libc)Flushing Buffers.
* __freadable: (libc)Opening Streams.
* __freading: (libc)Opening Streams.
* __fsetlocking: (libc)Streams and Threads.
* __fwritable: (libc)Opening Streams.
* __fwriting: (libc)Opening Streams.
* __gconv_end_fct: (libc)glibc iconv Implementation.
* __gconv_fct: (libc)glibc iconv Implementation.
* __gconv_init_fct: (libc)glibc iconv Implementation.
* __ppc_get_timebase: (libc)PowerPC.
* __ppc_get_timebase_freq: (libc)PowerPC.
* __ppc_mdoio: (libc)PowerPC.
* __ppc_mdoom: (libc)PowerPC.
* __ppc_set_ppr_low: (libc)PowerPC.
* __ppc_set_ppr_med: (libc)PowerPC.
* __ppc_set_ppr_med_high: (libc)PowerPC.
* __ppc_set_ppr_med_low: (libc)PowerPC.
* __ppc_set_ppr_very_low: (libc)PowerPC.
* __ppc_yield: (libc)PowerPC.
* __riscv_flush_icache: (libc)RISC-V.
* __va_copy: (libc)Argument Macros.
* __x86_get_cpuid_feature_leaf: (libc)X86.
* _exit: (libc)Termination Internals.
* _flushlbf: (libc)Flushing Buffers.
* _tolower: (libc)Case Conversion.
* _toupper: (libc)Case Conversion.
* a64l: (libc)Encode Binary Data.
* abort: (libc)Aborting a Program.
* abs: (libc)Absolute Value.
* accept: (libc)Accepting Connections.
* access: (libc)Testing File Access.
* acos: (libc)Inverse Trig Functions.
* acosf: (libc)Inverse Trig Functions.
* acosfN: (libc)Inverse Trig Functions.
* acosfNx: (libc)Inverse Trig Functions.
* acosh: (libc)Hyperbolic Functions.
* acoshf: (libc)Hyperbolic Functions.
* acoshfN: (libc)Hyperbolic Functions.
* acoshfNx: (libc)Hyperbolic Functions.
* acoshl: (libc)Hyperbolic Functions.
* acosl: (libc)Inverse Trig Functions.
* addmntent: (libc)mtab.
* addseverity: (libc)Adding Severity Classes.
* adjtime: (libc)Setting and Adjusting the Time.
* adjtimex: (libc)Setting and Adjusting the Time.
* aio_cancel64: (libc)Cancel AIO Operations.
* aio_cancel: (libc)Cancel AIO Operations.
* aio_error64: (libc)Status of AIO Operations.
* aio_error: (libc)Status of AIO Operations.
* aio_fsync64: (libc)Synchronizing AIO Operations.
* aio_fsync: (libc)Synchronizing AIO Operations.
* aio_init: (libc)Configuration of AIO.
* aio_read64: (libc)Asynchronous Reads/Writes.
* aio_read: (libc)Asynchronous Reads/Writes.
* aio_return64: (libc)Status of AIO Operations.
* aio_return: (libc)Status of AIO Operations.
* aio_suspend64: (libc)Synchronizing AIO Operations.
* aio_suspend: (libc)Synchronizing AIO Operations.
* aio_write64: (libc)Asynchronous Reads/Writes.
* aio_write: (libc)Asynchronous Reads/Writes.
* alarm: (libc)Setting an Alarm.
* aligned_alloc: (libc)Aligned Memory Blocks.
* alloca: (libc)Variable Size Automatic.
* alphasort64: (libc)Scanning Directory Content.
* alphasort: (libc)Scanning Directory Content.
* argp_error: (libc)Argp Helper Functions.
* argp_failure: (libc)Argp Helper Functions.
* argp_help: (libc)Argp Help.
* argp_parse: (libc)Argp.
* argp_state_help: (libc)Argp Helper Functions.
* argp_usage: (libc)Argp Helper Functions.
* argz_add: (libc)Argz Functions.
* argz_add_sep: (libc)Argz Functions.
* argz_append: (libc)Argz Functions.
* argz_count: (libc)Argz Functions.
* argz_create: (libc)Argz Functions.
* argz_create_sep: (libc)Argz Functions.
* argz_delete: (libc)Argz Functions.
* argz_extract: (libc)Argz Functions.
* argz_insert: (libc)Argz Functions.
* argz_next: (libc)Argz Functions.
* argz_replace: (libc)Argz Functions.
* argz_stringify: (libc)Argz Functions.
* asctime: (libc)Formatting Calendar Time.
* asctime_r: (libc)Formatting Calendar Time.
* asin: (libc)Inverse Trig Functions.
* asinf: (libc)Inverse Trig Functions.
* asinfN: (libc)Inverse Trig Functions.
* asinfNx: (libc)Inverse Trig Functions.
* asinh: (libc)Hyperbolic Functions.
* asinhf: (libc)Hyperbolic Functions.
* asinhfN: (libc)Hyperbolic Functions.
* asinhfNx: (libc)Hyperbolic Functions.
* asinhl: (libc)Hyperbolic Functions.
* asinl: (libc)Inverse Trig Functions.
* asprintf: (libc)Dynamic Output.
* assert: (libc)Consistency Checking.
* assert_perror: (libc)Consistency Checking.
* atan2: (libc)Inverse Trig Functions.
* atan2f: (libc)Inverse Trig Functions.
* atan2fN: (libc)Inverse Trig Functions.
* atan2fNx: (libc)Inverse Trig Functions.
* atan2l: (libc)Inverse Trig Functions.
* atan: (libc)Inverse Trig Functions.
* atanf: (libc)Inverse Trig Functions.
* atanfN: (libc)Inverse Trig Functions.
* atanfNx: (libc)Inverse Trig Functions.
* atanh: (libc)Hyperbolic Functions.
* atanhf: (libc)Hyperbolic Functions.
* atanhfN: (libc)Hyperbolic Functions.
* atanhfNx: (libc)Hyperbolic Functions.
* atanhl: (libc)Hyperbolic Functions.
* atanl: (libc)Inverse Trig Functions.
* atexit: (libc)Cleanups on Exit.
* atof: (libc)Parsing of Floats.
* atoi: (libc)Parsing of Integers.
* atol: (libc)Parsing of Integers.
* atoll: (libc)Parsing of Integers.
* backtrace: (libc)Backtraces.
* backtrace_symbols: (libc)Backtraces.
* backtrace_symbols_fd: (libc)Backtraces.
* basename: (libc)Finding Tokens in a String.
* basename: (libc)Finding Tokens in a String.
* bcmp: (libc)String/Array Comparison.
* bcopy: (libc)Copying Strings and Arrays.
* bind: (libc)Setting Address.
* bind_textdomain_codeset: (libc)Charset conversion in gettext.
* bindtextdomain: (libc)Locating gettext catalog.
* brk: (libc)Resizing the Data Segment.
* bsearch: (libc)Array Search Function.
* btowc: (libc)Converting a Character.
* bzero: (libc)Copying Strings and Arrays.
* cabs: (libc)Absolute Value.
* cabsf: (libc)Absolute Value.
* cabsfN: (libc)Absolute Value.
* cabsfNx: (libc)Absolute Value.
* cabsl: (libc)Absolute Value.
* cacos: (libc)Inverse Trig Functions.
* cacosf: (libc)Inverse Trig Functions.
* cacosfN: (libc)Inverse Trig Functions.
* cacosfNx: (libc)Inverse Trig Functions.
* cacosh: (libc)Hyperbolic Functions.
* cacoshf: (libc)Hyperbolic Functions.
* cacoshfN: (libc)Hyperbolic Functions.
* cacoshfNx: (libc)Hyperbolic Functions.
* cacoshl: (libc)Hyperbolic Functions.
* cacosl: (libc)Inverse Trig Functions.
* call_once: (libc)Call Once.
* calloc: (libc)Allocating Cleared Space.
* canonicalize: (libc)FP Bit Twiddling.
* canonicalize_file_name: (libc)Symbolic Links.
* canonicalizef: (libc)FP Bit Twiddling.
* canonicalizefN: (libc)FP Bit Twiddling.
* canonicalizefNx: (libc)FP Bit Twiddling.
* canonicalizel: (libc)FP Bit Twiddling.
* carg: (libc)Operations on Complex.
* cargf: (libc)Operations on Complex.
* cargfN: (libc)Operations on Complex.
* cargfNx: (libc)Operations on Complex.
* cargl: (libc)Operations on Complex.
* casin: (libc)Inverse Trig Functions.
* casinf: (libc)Inverse Trig Functions.
* casinfN: (libc)Inverse Trig Functions.
* casinfNx: (libc)Inverse Trig Functions.
* casinh: (libc)Hyperbolic Functions.
* casinhf: (libc)Hyperbolic Functions.
* casinhfN: (libc)Hyperbolic Functions.
* casinhfNx: (libc)Hyperbolic Functions.
* casinhl: (libc)Hyperbolic Functions.
* casinl: (libc)Inverse Trig Functions.
* catan: (libc)Inverse Trig Functions.
* catanf: (libc)Inverse Trig Functions.
* catanfN: (libc)Inverse Trig Functions.
* catanfNx: (libc)Inverse Trig Functions.
* catanh: (libc)Hyperbolic Functions.
* catanhf: (libc)Hyperbolic Functions.
* catanhfN: (libc)Hyperbolic Functions.
* catanhfNx: (libc)Hyperbolic Functions.
* catanhl: (libc)Hyperbolic Functions.
* catanl: (libc)Inverse Trig Functions.
* catclose: (libc)The catgets Functions.
* catgets: (libc)The catgets Functions.
* catopen: (libc)The catgets Functions.
* cbrt: (libc)Exponents and Logarithms.
* cbrtf: (libc)Exponents and Logarithms.
* cbrtfN: (libc)Exponents and Logarithms.
* cbrtfNx: (libc)Exponents and Logarithms.
* cbrtl: (libc)Exponents and Logarithms.
* ccos: (libc)Trig Functions.
* ccosf: (libc)Trig Functions.
* ccosfN: (libc)Trig Functions.
* ccosfNx: (libc)Trig Functions.
* ccosh: (libc)Hyperbolic Functions.
* ccoshf: (libc)Hyperbolic Functions.
* ccoshfN: (libc)Hyperbolic Functions.
* ccoshfNx: (libc)Hyperbolic Functions.
* ccoshl: (libc)Hyperbolic Functions.
* ccosl: (libc)Trig Functions.
* ceil: (libc)Rounding Functions.
* ceilf: (libc)Rounding Functions.
* ceilfN: (libc)Rounding Functions.
* ceilfNx: (libc)Rounding Functions.
* ceill: (libc)Rounding Functions.
* cexp: (libc)Exponents and Logarithms.
* cexpf: (libc)Exponents and Logarithms.
* cexpfN: (libc)Exponents and Logarithms.
* cexpfNx: (libc)Exponents and Logarithms.
* cexpl: (libc)Exponents and Logarithms.
* cfgetispeed: (libc)Line Speed.
* cfgetospeed: (libc)Line Speed.
* cfmakeraw: (libc)Noncanonical Input.
* cfsetispeed: (libc)Line Speed.
* cfsetospeed: (libc)Line Speed.
* cfsetspeed: (libc)Line Speed.
* chdir: (libc)Working Directory.
* chmod: (libc)Setting Permissions.
* chown: (libc)File Owner.
* cimag: (libc)Operations on Complex.
* cimagf: (libc)Operations on Complex.
* cimagfN: (libc)Operations on Complex.
* cimagfNx: (libc)Operations on Complex.
* cimagl: (libc)Operations on Complex.
* clearenv: (libc)Environment Access.
* clearerr: (libc)Error Recovery.
* clearerr_unlocked: (libc)Error Recovery.
* clock: (libc)CPU Time.
* clock_getres: (libc)Getting the Time.
* clock_gettime: (libc)Getting the Time.
* clock_settime: (libc)Setting and Adjusting the Time.
* clog10: (libc)Exponents and Logarithms.
* clog10f: (libc)Exponents and Logarithms.
* clog10fN: (libc)Exponents and Logarithms.
* clog10fNx: (libc)Exponents and Logarithms.
* clog10l: (libc)Exponents and Logarithms.
* clog: (libc)Exponents and Logarithms.
* clogf: (libc)Exponents and Logarithms.
* clogfN: (libc)Exponents and Logarithms.
* clogfNx: (libc)Exponents and Logarithms.
* clogl: (libc)Exponents and Logarithms.
* close: (libc)Opening and Closing Files.
* closedir: (libc)Reading/Closing Directory.
* closelog: (libc)closelog.
* cnd_broadcast: (libc)ISO C Condition Variables.
* cnd_destroy: (libc)ISO C Condition Variables.
* cnd_init: (libc)ISO C Condition Variables.
* cnd_signal: (libc)ISO C Condition Variables.
* cnd_timedwait: (libc)ISO C Condition Variables.
* cnd_wait: (libc)ISO C Condition Variables.
* confstr: (libc)String Parameters.
* conj: (libc)Operations on Complex.
* conjf: (libc)Operations on Complex.
* conjfN: (libc)Operations on Complex.
* conjfNx: (libc)Operations on Complex.
* conjl: (libc)Operations on Complex.
* connect: (libc)Connecting.
* copy_file_range: (libc)Copying File Data.
* copysign: (libc)FP Bit Twiddling.
* copysignf: (libc)FP Bit Twiddling.
* copysignfN: (libc)FP Bit Twiddling.
* copysignfNx: (libc)FP Bit Twiddling.
* copysignl: (libc)FP Bit Twiddling.
* cos: (libc)Trig Functions.
* cosf: (libc)Trig Functions.
* cosfN: (libc)Trig Functions.
* cosfNx: (libc)Trig Functions.
* cosh: (libc)Hyperbolic Functions.
* coshf: (libc)Hyperbolic Functions.
* coshfN: (libc)Hyperbolic Functions.
* coshfNx: (libc)Hyperbolic Functions.
* coshl: (libc)Hyperbolic Functions.
* cosl: (libc)Trig Functions.
* cpow: (libc)Exponents and Logarithms.
* cpowf: (libc)Exponents and Logarithms.
* cpowfN: (libc)Exponents and Logarithms.
* cpowfNx: (libc)Exponents and Logarithms.
* cpowl: (libc)Exponents and Logarithms.
* cproj: (libc)Operations on Complex.
* cprojf: (libc)Operations on Complex.
* cprojfN: (libc)Operations on Complex.
* cprojfNx: (libc)Operations on Complex.
* cprojl: (libc)Operations on Complex.
* creal: (libc)Operations on Complex.
* crealf: (libc)Operations on Complex.
* crealfN: (libc)Operations on Complex.
* crealfNx: (libc)Operations on Complex.
* creall: (libc)Operations on Complex.
* creat64: (libc)Opening and Closing Files.
* creat: (libc)Opening and Closing Files.
* crypt: (libc)Passphrase Storage.
* crypt_r: (libc)Passphrase Storage.
* csin: (libc)Trig Functions.
* csinf: (libc)Trig Functions.
* csinfN: (libc)Trig Functions.
* csinfNx: (libc)Trig Functions.
* csinh: (libc)Hyperbolic Functions.
* csinhf: (libc)Hyperbolic Functions.
* csinhfN: (libc)Hyperbolic Functions.
* csinhfNx: (libc)Hyperbolic Functions.
* csinhl: (libc)Hyperbolic Functions.
* csinl: (libc)Trig Functions.
* csqrt: (libc)Exponents and Logarithms.
* csqrtf: (libc)Exponents and Logarithms.
* csqrtfN: (libc)Exponents and Logarithms.
* csqrtfNx: (libc)Exponents and Logarithms.
* csqrtl: (libc)Exponents and Logarithms.
* ctan: (libc)Trig Functions.
* ctanf: (libc)Trig Functions.
* ctanfN: (libc)Trig Functions.
* ctanfNx: (libc)Trig Functions.
* ctanh: (libc)Hyperbolic Functions.
* ctanhf: (libc)Hyperbolic Functions.
* ctanhfN: (libc)Hyperbolic Functions.
* ctanhfNx: (libc)Hyperbolic Functions.
* ctanhl: (libc)Hyperbolic Functions.
* ctanl: (libc)Trig Functions.
* ctermid: (libc)Identifying the Terminal.
* ctime: (libc)Formatting Calendar Time.
* ctime_r: (libc)Formatting Calendar Time.
* cuserid: (libc)Who Logged In.
* daddl: (libc)Misc FP Arithmetic.
* dcgettext: (libc)Translation with gettext.
* dcngettext: (libc)Advanced gettext functions.
* ddivl: (libc)Misc FP Arithmetic.
* dgettext: (libc)Translation with gettext.
* difftime: (libc)Calculating Elapsed Time.
* dirfd: (libc)Opening a Directory.
* dirname: (libc)Finding Tokens in a String.
* div: (libc)Integer Division.
* dmull: (libc)Misc FP Arithmetic.
* dngettext: (libc)Advanced gettext functions.
* drand48: (libc)SVID Random.
* drand48_r: (libc)SVID Random.
* drem: (libc)Remainder Functions.
* dremf: (libc)Remainder Functions.
* dreml: (libc)Remainder Functions.
* dsubl: (libc)Misc FP Arithmetic.
* dup2: (libc)Duplicating Descriptors.
* dup: (libc)Duplicating Descriptors.
* ecvt: (libc)System V Number Conversion.
* ecvt_r: (libc)System V Number Conversion.
* endfsent: (libc)fstab.
* endgrent: (libc)Scanning All Groups.
* endhostent: (libc)Host Names.
* endmntent: (libc)mtab.
* endnetent: (libc)Networks Database.
* endnetgrent: (libc)Lookup Netgroup.
* endprotoent: (libc)Protocols Database.
* endpwent: (libc)Scanning All Users.
* endservent: (libc)Services Database.
* endutent: (libc)Manipulating the Database.
* endutxent: (libc)XPG Functions.
* envz_add: (libc)Envz Functions.
* envz_entry: (libc)Envz Functions.
* envz_get: (libc)Envz Functions.
* envz_merge: (libc)Envz Functions.
* envz_remove: (libc)Envz Functions.
* envz_strip: (libc)Envz Functions.
* erand48: (libc)SVID Random.
* erand48_r: (libc)SVID Random.
* erf: (libc)Special Functions.
* erfc: (libc)Special Functions.
* erfcf: (libc)Special Functions.
* erfcfN: (libc)Special Functions.
* erfcfNx: (libc)Special Functions.
* erfcl: (libc)Special Functions.
* erff: (libc)Special Functions.
* erffN: (libc)Special Functions.
* erffNx: (libc)Special Functions.
* erfl: (libc)Special Functions.
* err: (libc)Error Messages.
* errno: (libc)Checking for Errors.
* error: (libc)Error Messages.
* error_at_line: (libc)Error Messages.
* errx: (libc)Error Messages.
* execl: (libc)Executing a File.
* execle: (libc)Executing a File.
* execlp: (libc)Executing a File.
* execv: (libc)Executing a File.
* execve: (libc)Executing a File.
* execvp: (libc)Executing a File.
* exit: (libc)Normal Termination.
* exp10: (libc)Exponents and Logarithms.
* exp10f: (libc)Exponents and Logarithms.
* exp10fN: (libc)Exponents and Logarithms.
* exp10fNx: (libc)Exponents and Logarithms.
* exp10l: (libc)Exponents and Logarithms.
* exp2: (libc)Exponents and Logarithms.
* exp2f: (libc)Exponents and Logarithms.
* exp2fN: (libc)Exponents and Logarithms.
* exp2fNx: (libc)Exponents and Logarithms.
* exp2l: (libc)Exponents and Logarithms.
* exp: (libc)Exponents and Logarithms.
* expf: (libc)Exponents and Logarithms.
* expfN: (libc)Exponents and Logarithms.
* expfNx: (libc)Exponents and Logarithms.
* expl: (libc)Exponents and Logarithms.
* explicit_bzero: (libc)Erasing Sensitive Data.
* expm1: (libc)Exponents and Logarithms.
* expm1f: (libc)Exponents and Logarithms.
* expm1fN: (libc)Exponents and Logarithms.
* expm1fNx: (libc)Exponents and Logarithms.
* expm1l: (libc)Exponents and Logarithms.
* fMaddfN: (libc)Misc FP Arithmetic.
* fMaddfNx: (libc)Misc FP Arithmetic.
* fMdivfN: (libc)Misc FP Arithmetic.
* fMdivfNx: (libc)Misc FP Arithmetic.
* fMmulfN: (libc)Misc FP Arithmetic.
* fMmulfNx: (libc)Misc FP Arithmetic.
* fMsubfN: (libc)Misc FP Arithmetic.
* fMsubfNx: (libc)Misc FP Arithmetic.
* fMxaddfN: (libc)Misc FP Arithmetic.
* fMxaddfNx: (libc)Misc FP Arithmetic.
* fMxdivfN: (libc)Misc FP Arithmetic.
* fMxdivfNx: (libc)Misc FP Arithmetic.
* fMxmulfN: (libc)Misc FP Arithmetic.
* fMxmulfNx: (libc)Misc FP Arithmetic.
* fMxsubfN: (libc)Misc FP Arithmetic.
* fMxsubfNx: (libc)Misc FP Arithmetic.
* fabs: (libc)Absolute Value.
* fabsf: (libc)Absolute Value.
* fabsfN: (libc)Absolute Value.
* fabsfNx: (libc)Absolute Value.
* fabsl: (libc)Absolute Value.
* fadd: (libc)Misc FP Arithmetic.
* faddl: (libc)Misc FP Arithmetic.
* fchdir: (libc)Working Directory.
* fchmod: (libc)Setting Permissions.
* fchown: (libc)File Owner.
* fclose: (libc)Closing Streams.
* fcloseall: (libc)Closing Streams.
* fcntl: (libc)Control Operations.
* fcvt: (libc)System V Number Conversion.
* fcvt_r: (libc)System V Number Conversion.
* fdatasync: (libc)Synchronizing I/O.
* fdim: (libc)Misc FP Arithmetic.
* fdimf: (libc)Misc FP Arithmetic.
* fdimfN: (libc)Misc FP Arithmetic.
* fdimfNx: (libc)Misc FP Arithmetic.
* fdiml: (libc)Misc FP Arithmetic.
* fdiv: (libc)Misc FP Arithmetic.
* fdivl: (libc)Misc FP Arithmetic.
* fdopen: (libc)Descriptors and Streams.
* fdopendir: (libc)Opening a Directory.
* feclearexcept: (libc)Status bit operations.
* fedisableexcept: (libc)Control Functions.
* feenableexcept: (libc)Control Functions.
* fegetenv: (libc)Control Functions.
* fegetexcept: (libc)Control Functions.
* fegetexceptflag: (libc)Status bit operations.
* fegetmode: (libc)Control Functions.
* fegetround: (libc)Rounding.
* feholdexcept: (libc)Control Functions.
* feof: (libc)EOF and Errors.
* feof_unlocked: (libc)EOF and Errors.
* feraiseexcept: (libc)Status bit operations.
* ferror: (libc)EOF and Errors.
* ferror_unlocked: (libc)EOF and Errors.
* fesetenv: (libc)Control Functions.
* fesetexcept: (libc)Status bit operations.
* fesetexceptflag: (libc)Status bit operations.
* fesetmode: (libc)Control Functions.
* fesetround: (libc)Rounding.
* fetestexcept: (libc)Status bit operations.
* fetestexceptflag: (libc)Status bit operations.
* feupdateenv: (libc)Control Functions.
* fexecve: (libc)Executing a File.
* fflush: (libc)Flushing Buffers.
* fflush_unlocked: (libc)Flushing Buffers.
* fgetc: (libc)Character Input.
* fgetc_unlocked: (libc)Character Input.
* fgetgrent: (libc)Scanning All Groups.
* fgetgrent_r: (libc)Scanning All Groups.
* fgetpos64: (libc)Portable Positioning.
* fgetpos: (libc)Portable Positioning.
* fgetpwent: (libc)Scanning All Users.
* fgetpwent_r: (libc)Scanning All Users.
* fgets: (libc)Line Input.
* fgets_unlocked: (libc)Line Input.
* fgetwc: (libc)Character Input.
* fgetwc_unlocked: (libc)Character Input.
* fgetws: (libc)Line Input.
* fgetws_unlocked: (libc)Line Input.
* fileno: (libc)Descriptors and Streams.
* fileno_unlocked: (libc)Descriptors and Streams.
* finite: (libc)Floating Point Classes.
* finitef: (libc)Floating Point Classes.
* finitel: (libc)Floating Point Classes.
* flockfile: (libc)Streams and Threads.
* floor: (libc)Rounding Functions.
* floorf: (libc)Rounding Functions.
* floorfN: (libc)Rounding Functions.
* floorfNx: (libc)Rounding Functions.
* floorl: (libc)Rounding Functions.
* fma: (libc)Misc FP Arithmetic.
* fmaf: (libc)Misc FP Arithmetic.
* fmafN: (libc)Misc FP Arithmetic.
* fmafNx: (libc)Misc FP Arithmetic.
* fmal: (libc)Misc FP Arithmetic.
* fmax: (libc)Misc FP Arithmetic.
* fmaxf: (libc)Misc FP Arithmetic.
* fmaxfN: (libc)Misc FP Arithmetic.
* fmaxfNx: (libc)Misc FP Arithmetic.
* fmaxl: (libc)Misc FP Arithmetic.
* fmaxmag: (libc)Misc FP Arithmetic.
* fmaxmagf: (libc)Misc FP Arithmetic.
* fmaxmagfN: (libc)Misc FP Arithmetic.
* fmaxmagfNx: (libc)Misc FP Arithmetic.
* fmaxmagl: (libc)Misc FP Arithmetic.
* fmemopen: (libc)String Streams.
* fmin: (libc)Misc FP Arithmetic.
* fminf: (libc)Misc FP Arithmetic.
* fminfN: (libc)Misc FP Arithmetic.
* fminfNx: (libc)Misc FP Arithmetic.
* fminl: (libc)Misc FP Arithmetic.
* fminmag: (libc)Misc FP Arithmetic.
* fminmagf: (libc)Misc FP Arithmetic.
* fminmagfN: (libc)Misc FP Arithmetic.
* fminmagfNx: (libc)Misc FP Arithmetic.
* fminmagl: (libc)Misc FP Arithmetic.
* fmod: (libc)Remainder Functions.
* fmodf: (libc)Remainder Functions.
* fmodfN: (libc)Remainder Functions.
* fmodfNx: (libc)Remainder Functions.
* fmodl: (libc)Remainder Functions.
* fmtmsg: (libc)Printing Formatted Messages.
* fmul: (libc)Misc FP Arithmetic.
* fmull: (libc)Misc FP Arithmetic.
* fnmatch: (libc)Wildcard Matching.
* fopen64: (libc)Opening Streams.
* fopen: (libc)Opening Streams.
* fopencookie: (libc)Streams and Cookies.
* fork: (libc)Creating a Process.
* forkpty: (libc)Pseudo-Terminal Pairs.
* fpathconf: (libc)Pathconf.
* fpclassify: (libc)Floating Point Classes.
* fprintf: (libc)Formatted Output Functions.
* fputc: (libc)Simple Output.
* fputc_unlocked: (libc)Simple Output.
* fputs: (libc)Simple Output.
* fputs_unlocked: (libc)Simple Output.
* fputwc: (libc)Simple Output.
* fputwc_unlocked: (libc)Simple Output.
* fputws: (libc)Simple Output.
* fputws_unlocked: (libc)Simple Output.
* fread: (libc)Block Input/Output.
* fread_unlocked: (libc)Block Input/Output.
* free: (libc)Freeing after Malloc.
* freopen64: (libc)Opening Streams.
* freopen: (libc)Opening Streams.
* frexp: (libc)Normalization Functions.
* frexpf: (libc)Normalization Functions.
* frexpfN: (libc)Normalization Functions.
* frexpfNx: (libc)Normalization Functions.
* frexpl: (libc)Normalization Functions.
* fromfp: (libc)Rounding Functions.
* fromfpf: (libc)Rounding Functions.
* fromfpfN: (libc)Rounding Functions.
* fromfpfNx: (libc)Rounding Functions.
* fromfpl: (libc)Rounding Functions.
* fromfpx: (libc)Rounding Functions.
* fromfpxf: (libc)Rounding Functions.
* fromfpxfN: (libc)Rounding Functions.
* fromfpxfNx: (libc)Rounding Functions.
* fromfpxl: (libc)Rounding Functions.
* fscanf: (libc)Formatted Input Functions.
* fseek: (libc)File Positioning.
* fseeko64: (libc)File Positioning.
* fseeko: (libc)File Positioning.
* fsetpos64: (libc)Portable Positioning.
* fsetpos: (libc)Portable Positioning.
* fstat64: (libc)Reading Attributes.
* fstat: (libc)Reading Attributes.
* fsub: (libc)Misc FP Arithmetic.
* fsubl: (libc)Misc FP Arithmetic.
* fsync: (libc)Synchronizing I/O.
* ftell: (libc)File Positioning.
* ftello64: (libc)File Positioning.
* ftello: (libc)File Positioning.
* ftruncate64: (libc)File Size.
* ftruncate: (libc)File Size.
* ftrylockfile: (libc)Streams and Threads.
* ftw64: (libc)Working with Directory Trees.
* ftw: (libc)Working with Directory Trees.
* funlockfile: (libc)Streams and Threads.
* futimes: (libc)File Times.
* fwide: (libc)Streams and I18N.
* fwprintf: (libc)Formatted Output Functions.
* fwrite: (libc)Block Input/Output.
* fwrite_unlocked: (libc)Block Input/Output.
* fwscanf: (libc)Formatted Input Functions.
* gamma: (libc)Special Functions.
* gammaf: (libc)Special Functions.
* gammal: (libc)Special Functions.
* gcvt: (libc)System V Number Conversion.
* get_avphys_pages: (libc)Query Memory Parameters.
* get_current_dir_name: (libc)Working Directory.
* get_nprocs: (libc)Processor Resources.
* get_nprocs_conf: (libc)Processor Resources.
* get_phys_pages: (libc)Query Memory Parameters.
* getauxval: (libc)Auxiliary Vector.
* getc: (libc)Character Input.
* getc_unlocked: (libc)Character Input.
* getchar: (libc)Character Input.
* getchar_unlocked: (libc)Character Input.
* getcontext: (libc)System V contexts.
* getcpu: (libc)CPU Affinity.
* getcwd: (libc)Working Directory.
* getdate: (libc)General Time String Parsing.
* getdate_r: (libc)General Time String Parsing.
* getdelim: (libc)Line Input.
* getdents64: (libc)Low-level Directory Access.
* getdomainnname: (libc)Host Identification.
* getegid: (libc)Reading Persona.
* getentropy: (libc)Unpredictable Bytes.
* getenv: (libc)Environment Access.
* geteuid: (libc)Reading Persona.
* getfsent: (libc)fstab.
* getfsfile: (libc)fstab.
* getfsspec: (libc)fstab.
* getgid: (libc)Reading Persona.
* getgrent: (libc)Scanning All Groups.
* getgrent_r: (libc)Scanning All Groups.
* getgrgid: (libc)Lookup Group.
* getgrgid_r: (libc)Lookup Group.
* getgrnam: (libc)Lookup Group.
* getgrnam_r: (libc)Lookup Group.
* getgrouplist: (libc)Setting Groups.
* getgroups: (libc)Reading Persona.
* gethostbyaddr: (libc)Host Names.
* gethostbyaddr_r: (libc)Host Names.
* gethostbyname2: (libc)Host Names.
* gethostbyname2_r: (libc)Host Names.
* gethostbyname: (libc)Host Names.
* gethostbyname_r: (libc)Host Names.
* gethostent: (libc)Host Names.
* gethostid: (libc)Host Identification.
* gethostname: (libc)Host Identification.
* getitimer: (libc)Setting an Alarm.
* getline: (libc)Line Input.
* getloadavg: (libc)Processor Resources.
* getlogin: (libc)Who Logged In.
* getmntent: (libc)mtab.
* getmntent_r: (libc)mtab.
* getnetbyaddr: (libc)Networks Database.
* getnetbyname: (libc)Networks Database.
* getnetent: (libc)Networks Database.
* getnetgrent: (libc)Lookup Netgroup.
* getnetgrent_r: (libc)Lookup Netgroup.
* getopt: (libc)Using Getopt.
* getopt_long: (libc)Getopt Long Options.
* getopt_long_only: (libc)Getopt Long Options.
* getpagesize: (libc)Query Memory Parameters.
* getpass: (libc)getpass.
* getpayload: (libc)FP Bit Twiddling.
* getpayloadf: (libc)FP Bit Twiddling.
* getpayloadfN: (libc)FP Bit Twiddling.
* getpayloadfNx: (libc)FP Bit Twiddling.
* getpayloadl: (libc)FP Bit Twiddling.
* getpeername: (libc)Who is Connected.
* getpgid: (libc)Process Group Functions.
* getpgrp: (libc)Process Group Functions.
* getpid: (libc)Process Identification.
* getppid: (libc)Process Identification.
* getpriority: (libc)Traditional Scheduling Functions.
* getprotobyname: (libc)Protocols Database.
* getprotobynumber: (libc)Protocols Database.
* getprotoent: (libc)Protocols Database.
* getpt: (libc)Allocation.
* getpwent: (libc)Scanning All Users.
* getpwent_r: (libc)Scanning All Users.
* getpwnam: (libc)Lookup User.
* getpwnam_r: (libc)Lookup User.
* getpwuid: (libc)Lookup User.
* getpwuid_r: (libc)Lookup User.
* getrandom: (libc)Unpredictable Bytes.
* getrlimit64: (libc)Limits on Resources.
* getrlimit: (libc)Limits on Resources.
* getrusage: (libc)Resource Usage.
* gets: (libc)Line Input.
* getservbyname: (libc)Services Database.
* getservbyport: (libc)Services Database.
* getservent: (libc)Services Database.
* getsid: (libc)Process Group Functions.
* getsockname: (libc)Reading Address.
* getsockopt: (libc)Socket Option Functions.
* getsubopt: (libc)Suboptions.
* gettext: (libc)Translation with gettext.
* gettid: (libc)Process Identification.
* gettimeofday: (libc)Getting the Time.
* getuid: (libc)Reading Persona.
* getumask: (libc)Setting Permissions.
* getutent: (libc)Manipulating the Database.
* getutent_r: (libc)Manipulating the Database.
* getutid: (libc)Manipulating the Database.
* getutid_r: (libc)Manipulating the Database.
* getutline: (libc)Manipulating the Database.
* getutline_r: (libc)Manipulating the Database.
* getutmp: (libc)XPG Functions.
* getutmpx: (libc)XPG Functions.
* getutxent: (libc)XPG Functions.
* getutxid: (libc)XPG Functions.
* getutxline: (libc)XPG Functions.
* getw: (libc)Character Input.
* getwc: (libc)Character Input.
* getwc_unlocked: (libc)Character Input.
* getwchar: (libc)Character Input.
* getwchar_unlocked: (libc)Character Input.
* getwd: (libc)Working Directory.
* glob64: (libc)Calling Glob.
* glob: (libc)Calling Glob.
* globfree64: (libc)More Flags for Globbing.
* globfree: (libc)More Flags for Globbing.
* gmtime: (libc)Broken-down Time.
* gmtime_r: (libc)Broken-down Time.
* grantpt: (libc)Allocation.
* gsignal: (libc)Signaling Yourself.
* gtty: (libc)BSD Terminal Modes.
* hasmntopt: (libc)mtab.
* hcreate: (libc)Hash Search Function.
* hcreate_r: (libc)Hash Search Function.
* hdestroy: (libc)Hash Search Function.
* hdestroy_r: (libc)Hash Search Function.
* hsearch: (libc)Hash Search Function.
* hsearch_r: (libc)Hash Search Function.
* htonl: (libc)Byte Order.
* htons: (libc)Byte Order.
* hypot: (libc)Exponents and Logarithms.
* hypotf: (libc)Exponents and Logarithms.
* hypotfN: (libc)Exponents and Logarithms.
* hypotfNx: (libc)Exponents and Logarithms.
* hypotl: (libc)Exponents and Logarithms.
* iconv: (libc)Generic Conversion Interface.
* iconv_close: (libc)Generic Conversion Interface.
* iconv_open: (libc)Generic Conversion Interface.
* if_freenameindex: (libc)Interface Naming.
* if_indextoname: (libc)Interface Naming.
* if_nameindex: (libc)Interface Naming.
* if_nametoindex: (libc)Interface Naming.
* ilogb: (libc)Exponents and Logarithms.
* ilogbf: (libc)Exponents and Logarithms.
* ilogbfN: (libc)Exponents and Logarithms.
* ilogbfNx: (libc)Exponents and Logarithms.
* ilogbl: (libc)Exponents and Logarithms.
* imaxabs: (libc)Absolute Value.
* imaxdiv: (libc)Integer Division.
* in6addr_any: (libc)Host Address Data Type.
* in6addr_loopback: (libc)Host Address Data Type.
* index: (libc)Search Functions.
* inet_addr: (libc)Host Address Functions.
* inet_aton: (libc)Host Address Functions.
* inet_lnaof: (libc)Host Address Functions.
* inet_makeaddr: (libc)Host Address Functions.
* inet_netof: (libc)Host Address Functions.
* inet_network: (libc)Host Address Functions.
* inet_ntoa: (libc)Host Address Functions.
* inet_ntop: (libc)Host Address Functions.
* inet_pton: (libc)Host Address Functions.
* initgroups: (libc)Setting Groups.
* initstate: (libc)BSD Random.
* initstate_r: (libc)BSD Random.
* innetgr: (libc)Netgroup Membership.
* ioctl: (libc)IOCTLs.
* isalnum: (libc)Classification of Characters.
* isalpha: (libc)Classification of Characters.
* isascii: (libc)Classification of Characters.
* isatty: (libc)Is It a Terminal.
* isblank: (libc)Classification of Characters.
* iscanonical: (libc)Floating Point Classes.
* iscntrl: (libc)Classification of Characters.
* isdigit: (libc)Classification of Characters.
* iseqsig: (libc)FP Comparison Functions.
* isfinite: (libc)Floating Point Classes.
* isgraph: (libc)Classification of Characters.
* isgreater: (libc)FP Comparison Functions.
* isgreaterequal: (libc)FP Comparison Functions.
* isinf: (libc)Floating Point Classes.
* isinff: (libc)Floating Point Classes.
* isinfl: (libc)Floating Point Classes.
* isless: (libc)FP Comparison Functions.
* islessequal: (libc)FP Comparison Functions.
* islessgreater: (libc)FP Comparison Functions.
* islower: (libc)Classification of Characters.
* isnan: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnanf: (libc)Floating Point Classes.
* isnanl: (libc)Floating Point Classes.
* isnormal: (libc)Floating Point Classes.
* isprint: (libc)Classification of Characters.
* ispunct: (libc)Classification of Characters.
* issignaling: (libc)Floating Point Classes.
* isspace: (libc)Classification of Characters.
* issubnormal: (libc)Floating Point Classes.
* isunordered: (libc)FP Comparison Functions.
* isupper: (libc)Classification of Characters.
* iswalnum: (libc)Classification of Wide Characters.
* iswalpha: (libc)Classification of Wide Characters.
* iswblank: (libc)Classification of Wide Characters.
* iswcntrl: (libc)Classification of Wide Characters.
* iswctype: (libc)Classification of Wide Characters.
* iswdigit: (libc)Classification of Wide Characters.
* iswgraph: (libc)Classification of Wide Characters.
* iswlower: (libc)Classification of Wide Characters.
* iswprint: (libc)Classification of Wide Characters.
* iswpunct: (libc)Classification of Wide Characters.
* iswspace: (libc)Classification of Wide Characters.
* iswupper: (libc)Classification of Wide Characters.
* iswxdigit: (libc)Classification of Wide Characters.
* isxdigit: (libc)Classification of Characters.
* iszero: (libc)Floating Point Classes.
* j0: (libc)Special Functions.
* j0f: (libc)Special Functions.
* j0fN: (libc)Special Functions.
* j0fNx: (libc)Special Functions.
* j0l: (libc)Special Functions.
* j1: (libc)Special Functions.
* j1f: (libc)Special Functions.
* j1fN: (libc)Special Functions.
* j1fNx: (libc)Special Functions.
* j1l: (libc)Special Functions.
* jn: (libc)Special Functions.
* jnf: (libc)Special Functions.
* jnfN: (libc)Special Functions.
* jnfNx: (libc)Special Functions.
* jnl: (libc)Special Functions.
* jrand48: (libc)SVID Random.
* jrand48_r: (libc)SVID Random.
* kill: (libc)Signaling Another Process.
* killpg: (libc)Signaling Another Process.
* l64a: (libc)Encode Binary Data.
* labs: (libc)Absolute Value.
* lcong48: (libc)SVID Random.
* lcong48_r: (libc)SVID Random.
* ldexp: (libc)Normalization Functions.
* ldexpf: (libc)Normalization Functions.
* ldexpfN: (libc)Normalization Functions.
* ldexpfNx: (libc)Normalization Functions.
* ldexpl: (libc)Normalization Functions.
* ldiv: (libc)Integer Division.
* lfind: (libc)Array Search Function.
* lgamma: (libc)Special Functions.
* lgamma_r: (libc)Special Functions.
* lgammaf: (libc)Special Functions.
* lgammafN: (libc)Special Functions.
* lgammafN_r: (libc)Special Functions.
* lgammafNx: (libc)Special Functions.
* lgammafNx_r: (libc)Special Functions.
* lgammaf_r: (libc)Special Functions.
* lgammal: (libc)Special Functions.
* lgammal_r: (libc)Special Functions.
* link: (libc)Hard Links.
* linkat: (libc)Hard Links.
* lio_listio64: (libc)Asynchronous Reads/Writes.
* lio_listio: (libc)Asynchronous Reads/Writes.
* listen: (libc)Listening.
* llabs: (libc)Absolute Value.
* lldiv: (libc)Integer Division.
* llogb: (libc)Exponents and Logarithms.
* llogbf: (libc)Exponents and Logarithms.
* llogbfN: (libc)Exponents and Logarithms.
* llogbfNx: (libc)Exponents and Logarithms.
* llogbl: (libc)Exponents and Logarithms.
* llrint: (libc)Rounding Functions.
* llrintf: (libc)Rounding Functions.
* llrintfN: (libc)Rounding Functions.
* llrintfNx: (libc)Rounding Functions.
* llrintl: (libc)Rounding Functions.
* llround: (libc)Rounding Functions.
* llroundf: (libc)Rounding Functions.
* llroundfN: (libc)Rounding Functions.
* llroundfNx: (libc)Rounding Functions.
* llroundl: (libc)Rounding Functions.
* localeconv: (libc)The Lame Way to Locale Data.
* localtime: (libc)Broken-down Time.
* localtime_r: (libc)Broken-down Time.
* log10: (libc)Exponents and Logarithms.
* log10f: (libc)Exponents and Logarithms.
* log10fN: (libc)Exponents and Logarithms.
* log10fNx: (libc)Exponents and Logarithms.
* log10l: (libc)Exponents and Logarithms.
* log1p: (libc)Exponents and Logarithms.
* log1pf: (libc)Exponents and Logarithms.
* log1pfN: (libc)Exponents and Logarithms.
* log1pfNx: (libc)Exponents and Logarithms.
* log1pl: (libc)Exponents and Logarithms.
* log2: (libc)Exponents and Logarithms.
* log2f: (libc)Exponents and Logarithms.
* log2fN: (libc)Exponents and Logarithms.
* log2fNx: (libc)Exponents and Logarithms.
* log2l: (libc)Exponents and Logarithms.
* log: (libc)Exponents and Logarithms.
* logb: (libc)Exponents and Logarithms.
* logbf: (libc)Exponents and Logarithms.
* logbfN: (libc)Exponents and Logarithms.
* logbfNx: (libc)Exponents and Logarithms.
* logbl: (libc)Exponents and Logarithms.
* logf: (libc)Exponents and Logarithms.
* logfN: (libc)Exponents and Logarithms.
* logfNx: (libc)Exponents and Logarithms.
* login: (libc)Logging In and Out.
* login_tty: (libc)Logging In and Out.
* logl: (libc)Exponents and Logarithms.
* logout: (libc)Logging In and Out.
* logwtmp: (libc)Logging In and Out.
* longjmp: (libc)Non-Local Details.
* lrand48: (libc)SVID Random.
* lrand48_r: (libc)SVID Random.
* lrint: (libc)Rounding Functions.
* lrintf: (libc)Rounding Functions.
* lrintfN: (libc)Rounding Functions.
* lrintfNx: (libc)Rounding Functions.
* lrintl: (libc)Rounding Functions.
* lround: (libc)Rounding Functions.
* lroundf: (libc)Rounding Functions.
* lroundfN: (libc)Rounding Functions.
* lroundfNx: (libc)Rounding Functions.
* lroundl: (libc)Rounding Functions.
* lsearch: (libc)Array Search Function.
* lseek64: (libc)File Position Primitive.
* lseek: (libc)File Position Primitive.
* lstat64: (libc)Reading Attributes.
* lstat: (libc)Reading Attributes.
* lutimes: (libc)File Times.
* madvise: (libc)Memory-mapped I/O.
* makecontext: (libc)System V contexts.
* mallinfo2: (libc)Statistics of Malloc.
* malloc: (libc)Basic Allocation.
* mallopt: (libc)Malloc Tunable Parameters.
* mblen: (libc)Non-reentrant Character Conversion.
* mbrlen: (libc)Converting a Character.
* mbrtowc: (libc)Converting a Character.
* mbsinit: (libc)Keeping the state.
* mbsnrtowcs: (libc)Converting Strings.
* mbsrtowcs: (libc)Converting Strings.
* mbstowcs: (libc)Non-reentrant String Conversion.
* mbtowc: (libc)Non-reentrant Character Conversion.
* mcheck: (libc)Heap Consistency Checking.
* memalign: (libc)Aligned Memory Blocks.
* memccpy: (libc)Copying Strings and Arrays.
* memchr: (libc)Search Functions.
* memcmp: (libc)String/Array Comparison.
* memcpy: (libc)Copying Strings and Arrays.
* memfd_create: (libc)Memory-mapped I/O.
* memfrob: (libc)Obfuscating Data.
* memmem: (libc)Search Functions.
* memmove: (libc)Copying Strings and Arrays.
* mempcpy: (libc)Copying Strings and Arrays.
* memrchr: (libc)Search Functions.
* memset: (libc)Copying Strings and Arrays.
* mkdir: (libc)Creating Directories.
* mkdtemp: (libc)Temporary Files.
* mkfifo: (libc)FIFO Special Files.
* mknod: (libc)Making Special Files.
* mkstemp: (libc)Temporary Files.
* mktemp: (libc)Temporary Files.
* mktime: (libc)Broken-down Time.
* mlock2: (libc)Page Lock Functions.
* mlock: (libc)Page Lock Functions.
* mlockall: (libc)Page Lock Functions.
* mmap64: (libc)Memory-mapped I/O.
* mmap: (libc)Memory-mapped I/O.
* modf: (libc)Rounding Functions.
* modff: (libc)Rounding Functions.
* modffN: (libc)Rounding Functions.
* modffNx: (libc)Rounding Functions.
* modfl: (libc)Rounding Functions.
* mount: (libc)Mount-Unmount-Remount.
* mprobe: (libc)Heap Consistency Checking.
* mprotect: (libc)Memory Protection.
* mrand48: (libc)SVID Random.
* mrand48_r: (libc)SVID Random.
* mremap: (libc)Memory-mapped I/O.
* msync: (libc)Memory-mapped I/O.
* mtrace: (libc)Tracing malloc.
* mtx_destroy: (libc)ISO C Mutexes.
* mtx_init: (libc)ISO C Mutexes.
* mtx_lock: (libc)ISO C Mutexes.
* mtx_timedlock: (libc)ISO C Mutexes.
* mtx_trylock: (libc)ISO C Mutexes.
* mtx_unlock: (libc)ISO C Mutexes.
* munlock: (libc)Page Lock Functions.
* munlockall: (libc)Page Lock Functions.
* munmap: (libc)Memory-mapped I/O.
* muntrace: (libc)Tracing malloc.
* nan: (libc)FP Bit Twiddling.
* nanf: (libc)FP Bit Twiddling.
* nanfN: (libc)FP Bit Twiddling.
* nanfNx: (libc)FP Bit Twiddling.
* nanl: (libc)FP Bit Twiddling.
* nanosleep: (libc)Sleeping.
* nearbyint: (libc)Rounding Functions.
* nearbyintf: (libc)Rounding Functions.
* nearbyintfN: (libc)Rounding Functions.
* nearbyintfNx: (libc)Rounding Functions.
* nearbyintl: (libc)Rounding Functions.
* nextafter: (libc)FP Bit Twiddling.
* nextafterf: (libc)FP Bit Twiddling.
* nextafterfN: (libc)FP Bit Twiddling.
* nextafterfNx: (libc)FP Bit Twiddling.
* nextafterl: (libc)FP Bit Twiddling.
* nextdown: (libc)FP Bit Twiddling.
* nextdownf: (libc)FP Bit Twiddling.
* nextdownfN: (libc)FP Bit Twiddling.
* nextdownfNx: (libc)FP Bit Twiddling.
* nextdownl: (libc)FP Bit Twiddling.
* nexttoward: (libc)FP Bit Twiddling.
* nexttowardf: (libc)FP Bit Twiddling.
* nexttowardl: (libc)FP Bit Twiddling.
* nextup: (libc)FP Bit Twiddling.
* nextupf: (libc)FP Bit Twiddling.
* nextupfN: (libc)FP Bit Twiddling.
* nextupfNx: (libc)FP Bit Twiddling.
* nextupl: (libc)FP Bit Twiddling.
* nftw64: (libc)Working with Directory Trees.
* nftw: (libc)Working with Directory Trees.
* ngettext: (libc)Advanced gettext functions.
* nice: (libc)Traditional Scheduling Functions.
* nl_langinfo: (libc)The Elegant and Fast Way.
* nrand48: (libc)SVID Random.
* nrand48_r: (libc)SVID Random.
* ntohl: (libc)Byte Order.
* ntohs: (libc)Byte Order.
* ntp_adjtime: (libc)Setting and Adjusting the Time.
* ntp_gettime: (libc)Setting and Adjusting the Time.
* obstack_1grow: (libc)Growing Objects.
* obstack_1grow_fast: (libc)Extra Fast Growing.
* obstack_alignment_mask: (libc)Obstacks Data Alignment.
* obstack_alloc: (libc)Allocation in an Obstack.
* obstack_base: (libc)Status of an Obstack.
* obstack_blank: (libc)Growing Objects.
* obstack_blank_fast: (libc)Extra Fast Growing.
* obstack_chunk_size: (libc)Obstack Chunks.
* obstack_copy0: (libc)Allocation in an Obstack.
* obstack_copy: (libc)Allocation in an Obstack.
* obstack_finish: (libc)Growing Objects.
* obstack_free: (libc)Freeing Obstack Objects.
* obstack_grow0: (libc)Growing Objects.
* obstack_grow: (libc)Growing Objects.
* obstack_init: (libc)Preparing for Obstacks.
* obstack_int_grow: (libc)Growing Objects.
* obstack_int_grow_fast: (libc)Extra Fast Growing.
* obstack_next_free: (libc)Status of an Obstack.
* obstack_object_size: (libc)Growing Objects.
* obstack_object_size: (libc)Status of an Obstack.
* obstack_printf: (libc)Dynamic Output.
* obstack_ptr_grow: (libc)Growing Objects.
* obstack_ptr_grow_fast: (libc)Extra Fast Growing.
* obstack_room: (libc)Extra Fast Growing.
* obstack_vprintf: (libc)Variable Arguments Output.
* offsetof: (libc)Structure Measurement.
* on_exit: (libc)Cleanups on Exit.
* open64: (libc)Opening and Closing Files.
* open: (libc)Opening and Closing Files.
* open_memstream: (libc)String Streams.
* opendir: (libc)Opening a Directory.
* openlog: (libc)openlog.
* openpty: (libc)Pseudo-Terminal Pairs.
* parse_printf_format: (libc)Parsing a Template String.
* pathconf: (libc)Pathconf.
* pause: (libc)Using Pause.
* pclose: (libc)Pipe to a Subprocess.
* perror: (libc)Error Messages.
* pipe: (libc)Creating a Pipe.
* pkey_alloc: (libc)Memory Protection.
* pkey_free: (libc)Memory Protection.
* pkey_get: (libc)Memory Protection.
* pkey_mprotect: (libc)Memory Protection.
* pkey_set: (libc)Memory Protection.
* popen: (libc)Pipe to a Subprocess.
* posix_fallocate64: (libc)Storage Allocation.
* posix_fallocate: (libc)Storage Allocation.
* posix_memalign: (libc)Aligned Memory Blocks.
* pow: (libc)Exponents and Logarithms.
* powf: (libc)Exponents and Logarithms.
* powfN: (libc)Exponents and Logarithms.
* powfNx: (libc)Exponents and Logarithms.
* powl: (libc)Exponents and Logarithms.
* pread64: (libc)I/O Primitives.
* pread: (libc)I/O Primitives.
* preadv2: (libc)Scatter-Gather.
* preadv64: (libc)Scatter-Gather.
* preadv64v2: (libc)Scatter-Gather.
* preadv: (libc)Scatter-Gather.
* printf: (libc)Formatted Output Functions.
* printf_size: (libc)Predefined Printf Handlers.
* printf_size_info: (libc)Predefined Printf Handlers.
* psignal: (libc)Signal Messages.
* pthread_attr_getsigmask_np: (libc)Initial Thread Signal Mask.
* pthread_attr_setsigmask_np: (libc)Initial Thread Signal Mask.
* pthread_clockjoin_np: (libc)Waiting with Explicit Clocks.
* pthread_cond_clockwait: (libc)Waiting with Explicit Clocks.
* pthread_getattr_default_np: (libc)Default Thread Attributes.
* pthread_getspecific: (libc)Thread-specific Data.
* pthread_key_create: (libc)Thread-specific Data.
* pthread_key_delete: (libc)Thread-specific Data.
* pthread_rwlock_clockrdlock: (libc)Waiting with Explicit Clocks.
* pthread_rwlock_clockwrlock: (libc)Waiting with Explicit Clocks.
* pthread_setattr_default_np: (libc)Default Thread Attributes.
* pthread_setspecific: (libc)Thread-specific Data.
* pthread_timedjoin_np: (libc)Waiting with Explicit Clocks.
* pthread_tryjoin_np: (libc)Waiting with Explicit Clocks.
* ptsname: (libc)Allocation.
* ptsname_r: (libc)Allocation.
* putc: (libc)Simple Output.
* putc_unlocked: (libc)Simple Output.
* putchar: (libc)Simple Output.
* putchar_unlocked: (libc)Simple Output.
* putenv: (libc)Environment Access.
* putpwent: (libc)Writing a User Entry.
* puts: (libc)Simple Output.
* pututline: (libc)Manipulating the Database.
* pututxline: (libc)XPG Functions.
* putw: (libc)Simple Output.
* putwc: (libc)Simple Output.
* putwc_unlocked: (libc)Simple Output.
* putwchar: (libc)Simple Output.
* putwchar_unlocked: (libc)Simple Output.
* pwrite64: (libc)I/O Primitives.
* pwrite: (libc)I/O Primitives.
* pwritev2: (libc)Scatter-Gather.
* pwritev64: (libc)Scatter-Gather.
* pwritev64v2: (libc)Scatter-Gather.
* pwritev: (libc)Scatter-Gather.
* qecvt: (libc)System V Number Conversion.
* qecvt_r: (libc)System V Number Conversion.
* qfcvt: (libc)System V Number Conversion.
* qfcvt_r: (libc)System V Number Conversion.
* qgcvt: (libc)System V Number Conversion.
* qsort: (libc)Array Sort Function.
* raise: (libc)Signaling Yourself.
* rand: (libc)ISO Random.
* rand_r: (libc)ISO Random.
* random: (libc)BSD Random.
* random_r: (libc)BSD Random.
* rawmemchr: (libc)Search Functions.
* read: (libc)I/O Primitives.
* readdir64: (libc)Reading/Closing Directory.
* readdir64_r: (libc)Reading/Closing Directory.
* readdir: (libc)Reading/Closing Directory.
* readdir_r: (libc)Reading/Closing Directory.
* readlink: (libc)Symbolic Links.
* readv: (libc)Scatter-Gather.
* realloc: (libc)Changing Block Size.
* reallocarray: (libc)Changing Block Size.
* realpath: (libc)Symbolic Links.
* recv: (libc)Receiving Data.
* recvfrom: (libc)Receiving Datagrams.
* recvmsg: (libc)Receiving Datagrams.
* regcomp: (libc)POSIX Regexp Compilation.
* regerror: (libc)Regexp Cleanup.
* regexec: (libc)Matching POSIX Regexps.
* regfree: (libc)Regexp Cleanup.
* register_printf_function: (libc)Registering New Conversions.
* remainder: (libc)Remainder Functions.
* remainderf: (libc)Remainder Functions.
* remainderfN: (libc)Remainder Functions.
* remainderfNx: (libc)Remainder Functions.
* remainderl: (libc)Remainder Functions.
* remove: (libc)Deleting Files.
* rename: (libc)Renaming Files.
* rewind: (libc)File Positioning.
* rewinddir: (libc)Random Access Directory.
* rindex: (libc)Search Functions.
* rint: (libc)Rounding Functions.
* rintf: (libc)Rounding Functions.
* rintfN: (libc)Rounding Functions.
* rintfNx: (libc)Rounding Functions.
* rintl: (libc)Rounding Functions.
* rmdir: (libc)Deleting Files.
* round: (libc)Rounding Functions.
* roundeven: (libc)Rounding Functions.
* roundevenf: (libc)Rounding Functions.
* roundevenfN: (libc)Rounding Functions.
* roundevenfNx: (libc)Rounding Functions.
* roundevenl: (libc)Rounding Functions.
* roundf: (libc)Rounding Functions.
* roundfN: (libc)Rounding Functions.
* roundfNx: (libc)Rounding Functions.
* roundl: (libc)Rounding Functions.
* rpmatch: (libc)Yes-or-No Questions.
* sbrk: (libc)Resizing the Data Segment.
* scalb: (libc)Normalization Functions.
* scalbf: (libc)Normalization Functions.
* scalbl: (libc)Normalization Functions.
* scalbln: (libc)Normalization Functions.
* scalblnf: (libc)Normalization Functions.
* scalblnfN: (libc)Normalization Functions.
* scalblnfNx: (libc)Normalization Functions.
* scalblnl: (libc)Normalization Functions.
* scalbn: (libc)Normalization Functions.
* scalbnf: (libc)Normalization Functions.
* scalbnfN: (libc)Normalization Functions.
* scalbnfNx: (libc)Normalization Functions.
* scalbnl: (libc)Normalization Functions.
* scandir64: (libc)Scanning Directory Content.
* scandir: (libc)Scanning Directory Content.
* scanf: (libc)Formatted Input Functions.
* sched_get_priority_max: (libc)Basic Scheduling Functions.
* sched_get_priority_min: (libc)Basic Scheduling Functions.
* sched_getaffinity: (libc)CPU Affinity.
* sched_getparam: (libc)Basic Scheduling Functions.
* sched_getscheduler: (libc)Basic Scheduling Functions.
* sched_rr_get_interval: (libc)Basic Scheduling Functions.
* sched_setaffinity: (libc)CPU Affinity.
* sched_setparam: (libc)Basic Scheduling Functions.
* sched_setscheduler: (libc)Basic Scheduling Functions.
* sched_yield: (libc)Basic Scheduling Functions.
* secure_getenv: (libc)Environment Access.
* seed48: (libc)SVID Random.
* seed48_r: (libc)SVID Random.
* seekdir: (libc)Random Access Directory.
* select: (libc)Waiting for I/O.
* sem_clockwait: (libc)Waiting with Explicit Clocks.
* sem_close: (libc)Semaphores.
* sem_destroy: (libc)Semaphores.
* sem_getvalue: (libc)Semaphores.
* sem_init: (libc)Semaphores.
* sem_open: (libc)Semaphores.
* sem_post: (libc)Semaphores.
* sem_timedwait: (libc)Semaphores.
* sem_trywait: (libc)Semaphores.
* sem_unlink: (libc)Semaphores.
* sem_wait: (libc)Semaphores.
* semctl: (libc)Semaphores.
* semget: (libc)Semaphores.
* semop: (libc)Semaphores.
* semtimedop: (libc)Semaphores.
* send: (libc)Sending Data.
* sendmsg: (libc)Receiving Datagrams.
* sendto: (libc)Sending Datagrams.
* setbuf: (libc)Controlling Buffering.
* setbuffer: (libc)Controlling Buffering.
* setcontext: (libc)System V contexts.
* setdomainname: (libc)Host Identification.
* setegid: (libc)Setting Groups.
* setenv: (libc)Environment Access.
* seteuid: (libc)Setting User ID.
* setfsent: (libc)fstab.
* setgid: (libc)Setting Groups.
* setgrent: (libc)Scanning All Groups.
* setgroups: (libc)Setting Groups.
* sethostent: (libc)Host Names.
* sethostid: (libc)Host Identification.
* sethostname: (libc)Host Identification.
* setitimer: (libc)Setting an Alarm.
* setjmp: (libc)Non-Local Details.
* setlinebuf: (libc)Controlling Buffering.
* setlocale: (libc)Setting the Locale.
* setlogmask: (libc)setlogmask.
* setmntent: (libc)mtab.
* setnetent: (libc)Networks Database.
* setnetgrent: (libc)Lookup Netgroup.
* setpayload: (libc)FP Bit Twiddling.
* setpayloadf: (libc)FP Bit Twiddling.
* setpayloadfN: (libc)FP Bit Twiddling.
* setpayloadfNx: (libc)FP Bit Twiddling.
* setpayloadl: (libc)FP Bit Twiddling.
* setpayloadsig: (libc)FP Bit Twiddling.
* setpayloadsigf: (libc)FP Bit Twiddling.
* setpayloadsigfN: (libc)FP Bit Twiddling.
* setpayloadsigfNx: (libc)FP Bit Twiddling.
* setpayloadsigl: (libc)FP Bit Twiddling.
* setpgid: (libc)Process Group Functions.
* setpgrp: (libc)Process Group Functions.
* setpriority: (libc)Traditional Scheduling Functions.
* setprotoent: (libc)Protocols Database.
* setpwent: (libc)Scanning All Users.
* setregid: (libc)Setting Groups.
* setreuid: (libc)Setting User ID.
* setrlimit64: (libc)Limits on Resources.
* setrlimit: (libc)Limits on Resources.
* setservent: (libc)Services Database.
* setsid: (libc)Process Group Functions.
* setsockopt: (libc)Socket Option Functions.
* setstate: (libc)BSD Random.
* setstate_r: (libc)BSD Random.
* settimeofday: (libc)Setting and Adjusting the Time.
* setuid: (libc)Setting User ID.
* setutent: (libc)Manipulating the Database.
* setutxent: (libc)XPG Functions.
* setvbuf: (libc)Controlling Buffering.
* shm_open: (libc)Memory-mapped I/O.
* shm_unlink: (libc)Memory-mapped I/O.
* shutdown: (libc)Closing a Socket.
* sigabbrev_np: (libc)Signal Messages.
* sigaction: (libc)Advanced Signal Handling.
* sigaddset: (libc)Signal Sets.
* sigaltstack: (libc)Signal Stack.
* sigblock: (libc)BSD Signal Handling.
* sigdelset: (libc)Signal Sets.
* sigdescr_np: (libc)Signal Messages.
* sigemptyset: (libc)Signal Sets.
* sigfillset: (libc)Signal Sets.
* siginterrupt: (libc)BSD Signal Handling.
* sigismember: (libc)Signal Sets.
* siglongjmp: (libc)Non-Local Exits and Signals.
* sigmask: (libc)BSD Signal Handling.
* signal: (libc)Basic Signal Handling.
* signbit: (libc)FP Bit Twiddling.
* significand: (libc)Normalization Functions.
* significandf: (libc)Normalization Functions.
* significandl: (libc)Normalization Functions.
* sigpause: (libc)BSD Signal Handling.
* sigpending: (libc)Checking for Pending Signals.
* sigprocmask: (libc)Process Signal Mask.
* sigsetjmp: (libc)Non-Local Exits and Signals.
* sigsetmask: (libc)BSD Signal Handling.
* sigstack: (libc)Signal Stack.
* sigsuspend: (libc)Sigsuspend.
* sin: (libc)Trig Functions.
* sincos: (libc)Trig Functions.
* sincosf: (libc)Trig Functions.
* sincosfN: (libc)Trig Functions.
* sincosfNx: (libc)Trig Functions.
* sincosl: (libc)Trig Functions.
* sinf: (libc)Trig Functions.
* sinfN: (libc)Trig Functions.
* sinfNx: (libc)Trig Functions.
* sinh: (libc)Hyperbolic Functions.
* sinhf: (libc)Hyperbolic Functions.
* sinhfN: (libc)Hyperbolic Functions.
* sinhfNx: (libc)Hyperbolic Functions.
* sinhl: (libc)Hyperbolic Functions.
* sinl: (libc)Trig Functions.
* sleep: (libc)Sleeping.
* snprintf: (libc)Formatted Output Functions.
* socket: (libc)Creating a Socket.
* socketpair: (libc)Socket Pairs.
* sprintf: (libc)Formatted Output Functions.
* sqrt: (libc)Exponents and Logarithms.
* sqrtf: (libc)Exponents and Logarithms.
* sqrtfN: (libc)Exponents and Logarithms.
* sqrtfNx: (libc)Exponents and Logarithms.
* sqrtl: (libc)Exponents and Logarithms.
* srand48: (libc)SVID Random.
* srand48_r: (libc)SVID Random.
* srand: (libc)ISO Random.
* srandom: (libc)BSD Random.
* srandom_r: (libc)BSD Random.
* sscanf: (libc)Formatted Input Functions.
* ssignal: (libc)Basic Signal Handling.
* stat64: (libc)Reading Attributes.
* stat: (libc)Reading Attributes.
* stime: (libc)Setting and Adjusting the Time.
* stpcpy: (libc)Copying Strings and Arrays.
* stpncpy: (libc)Truncating Strings.
* strcasecmp: (libc)String/Array Comparison.
* strcasestr: (libc)Search Functions.
* strcat: (libc)Concatenating Strings.
* strchr: (libc)Search Functions.
* strchrnul: (libc)Search Functions.
* strcmp: (libc)String/Array Comparison.
* strcoll: (libc)Collation Functions.
* strcpy: (libc)Copying Strings and Arrays.
* strcspn: (libc)Search Functions.
* strdup: (libc)Copying Strings and Arrays.
* strdupa: (libc)Copying Strings and Arrays.
* strerror: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strerrordesc_np: (libc)Error Messages.
* strerrorname_np: (libc)Error Messages.
* strfmon: (libc)Formatting Numbers.
* strfromd: (libc)Printing of Floats.
* strfromf: (libc)Printing of Floats.
* strfromfN: (libc)Printing of Floats.
* strfromfNx: (libc)Printing of Floats.
* strfroml: (libc)Printing of Floats.
* strfry: (libc)Shuffling Bytes.
* strftime: (libc)Formatting Calendar Time.
* strlen: (libc)String Length.
* strncasecmp: (libc)String/Array Comparison.
* strncat: (libc)Truncating Strings.
* strncmp: (libc)String/Array Comparison.
* strncpy: (libc)Truncating Strings.
* strndup: (libc)Truncating Strings.
* strndupa: (libc)Truncating Strings.
* strnlen: (libc)String Length.
* strpbrk: (libc)Search Functions.
* strptime: (libc)Low-Level Time String Parsing.
* strrchr: (libc)Search Functions.
* strsep: (libc)Finding Tokens in a String.
* strsignal: (libc)Signal Messages.
* strspn: (libc)Search Functions.
* strstr: (libc)Search Functions.
* strtod: (libc)Parsing of Floats.
* strtof: (libc)Parsing of Floats.
* strtofN: (libc)Parsing of Floats.
* strtofNx: (libc)Parsing of Floats.
* strtoimax: (libc)Parsing of Integers.
* strtok: (libc)Finding Tokens in a String.
* strtok_r: (libc)Finding Tokens in a String.
* strtol: (libc)Parsing of Integers.
* strtold: (libc)Parsing of Floats.
* strtoll: (libc)Parsing of Integers.
* strtoq: (libc)Parsing of Integers.
* strtoul: (libc)Parsing of Integers.
* strtoull: (libc)Parsing of Integers.
* strtoumax: (libc)Parsing of Integers.
* strtouq: (libc)Parsing of Integers.
* strverscmp: (libc)String/Array Comparison.
* strxfrm: (libc)Collation Functions.
* stty: (libc)BSD Terminal Modes.
* swapcontext: (libc)System V contexts.
* swprintf: (libc)Formatted Output Functions.
* swscanf: (libc)Formatted Input Functions.
* symlink: (libc)Symbolic Links.
* sync: (libc)Synchronizing I/O.
* syscall: (libc)System Calls.
* sysconf: (libc)Sysconf Definition.
* syslog: (libc)syslog; vsyslog.
* system: (libc)Running a Command.
* sysv_signal: (libc)Basic Signal Handling.
* tan: (libc)Trig Functions.
* tanf: (libc)Trig Functions.
* tanfN: (libc)Trig Functions.
* tanfNx: (libc)Trig Functions.
* tanh: (libc)Hyperbolic Functions.
* tanhf: (libc)Hyperbolic Functions.
* tanhfN: (libc)Hyperbolic Functions.
* tanhfNx: (libc)Hyperbolic Functions.
* tanhl: (libc)Hyperbolic Functions.
* tanl: (libc)Trig Functions.
* tcdrain: (libc)Line Control.
* tcflow: (libc)Line Control.
* tcflush: (libc)Line Control.
* tcgetattr: (libc)Mode Functions.
* tcgetpgrp: (libc)Terminal Access Functions.
* tcgetsid: (libc)Terminal Access Functions.
* tcsendbreak: (libc)Line Control.
* tcsetattr: (libc)Mode Functions.
* tcsetpgrp: (libc)Terminal Access Functions.
* tdelete: (libc)Tree Search Function.
* tdestroy: (libc)Tree Search Function.
* telldir: (libc)Random Access Directory.
* tempnam: (libc)Temporary Files.
* textdomain: (libc)Locating gettext catalog.
* tfind: (libc)Tree Search Function.
* tgamma: (libc)Special Functions.
* tgammaf: (libc)Special Functions.
* tgammafN: (libc)Special Functions.
* tgammafNx: (libc)Special Functions.
* tgammal: (libc)Special Functions.
* tgkill: (libc)Signaling Another Process.
* thrd_create: (libc)ISO C Thread Management.
* thrd_current: (libc)ISO C Thread Management.
* thrd_detach: (libc)ISO C Thread Management.
* thrd_equal: (libc)ISO C Thread Management.
* thrd_exit: (libc)ISO C Thread Management.
* thrd_join: (libc)ISO C Thread Management.
* thrd_sleep: (libc)ISO C Thread Management.
* thrd_yield: (libc)ISO C Thread Management.
* time: (libc)Getting the Time.
* timegm: (libc)Broken-down Time.
* timelocal: (libc)Broken-down Time.
* times: (libc)Processor Time.
* tmpfile64: (libc)Temporary Files.
* tmpfile: (libc)Temporary Files.
* tmpnam: (libc)Temporary Files.
* tmpnam_r: (libc)Temporary Files.
* toascii: (libc)Case Conversion.
* tolower: (libc)Case Conversion.
* totalorder: (libc)FP Comparison Functions.
* totalorderf: (libc)FP Comparison Functions.
* totalorderfN: (libc)FP Comparison Functions.
* totalorderfNx: (libc)FP Comparison Functions.
* totalorderl: (libc)FP Comparison Functions.
* totalordermag: (libc)FP Comparison Functions.
* totalordermagf: (libc)FP Comparison Functions.
* totalordermagfN: (libc)FP Comparison Functions.
* totalordermagfNx: (libc)FP Comparison Functions.
* totalordermagl: (libc)FP Comparison Functions.
* toupper: (libc)Case Conversion.
* towctrans: (libc)Wide Character Case Conversion.
* towlower: (libc)Wide Character Case Conversion.
* towupper: (libc)Wide Character Case Conversion.
* trunc: (libc)Rounding Functions.
* truncate64: (libc)File Size.
* truncate: (libc)File Size.
* truncf: (libc)Rounding Functions.
* truncfN: (libc)Rounding Functions.
* truncfNx: (libc)Rounding Functions.
* truncl: (libc)Rounding Functions.
* tsearch: (libc)Tree Search Function.
* tss_create: (libc)ISO C Thread-local Storage.
* tss_delete: (libc)ISO C Thread-local Storage.
* tss_get: (libc)ISO C Thread-local Storage.
* tss_set: (libc)ISO C Thread-local Storage.
* ttyname: (libc)Is It a Terminal.
* ttyname_r: (libc)Is It a Terminal.
* twalk: (libc)Tree Search Function.
* twalk_r: (libc)Tree Search Function.
* tzset: (libc)Time Zone Functions.
* ufromfp: (libc)Rounding Functions.
* ufromfpf: (libc)Rounding Functions.
* ufromfpfN: (libc)Rounding Functions.
* ufromfpfNx: (libc)Rounding Functions.
* ufromfpl: (libc)Rounding Functions.
* ufromfpx: (libc)Rounding Functions.
* ufromfpxf: (libc)Rounding Functions.
* ufromfpxfN: (libc)Rounding Functions.
* ufromfpxfNx: (libc)Rounding Functions.
* ufromfpxl: (libc)Rounding Functions.
* ulimit: (libc)Limits on Resources.
* umask: (libc)Setting Permissions.
* umount2: (libc)Mount-Unmount-Remount.
* umount: (libc)Mount-Unmount-Remount.
* uname: (libc)Platform Type.
* ungetc: (libc)How Unread.
* ungetwc: (libc)How Unread.
* unlink: (libc)Deleting Files.
* unlockpt: (libc)Allocation.
* unsetenv: (libc)Environment Access.
* updwtmp: (libc)Manipulating the Database.
* utime: (libc)File Times.
* utimes: (libc)File Times.
* utmpname: (libc)Manipulating the Database.
* utmpxname: (libc)XPG Functions.
* va_arg: (libc)Argument Macros.
* va_copy: (libc)Argument Macros.
* va_end: (libc)Argument Macros.
* va_start: (libc)Argument Macros.
* valloc: (libc)Aligned Memory Blocks.
* vasprintf: (libc)Variable Arguments Output.
* verr: (libc)Error Messages.
* verrx: (libc)Error Messages.
* versionsort64: (libc)Scanning Directory Content.
* versionsort: (libc)Scanning Directory Content.
* vfork: (libc)Creating a Process.
* vfprintf: (libc)Variable Arguments Output.
* vfscanf: (libc)Variable Arguments Input.
* vfwprintf: (libc)Variable Arguments Output.
* vfwscanf: (libc)Variable Arguments Input.
* vlimit: (libc)Limits on Resources.
* vprintf: (libc)Variable Arguments Output.
* vscanf: (libc)Variable Arguments Input.
* vsnprintf: (libc)Variable Arguments Output.
* vsprintf: (libc)Variable Arguments Output.
* vsscanf: (libc)Variable Arguments Input.
* vswprintf: (libc)Variable Arguments Output.
* vswscanf: (libc)Variable Arguments Input.
* vsyslog: (libc)syslog; vsyslog.
* vwarn: (libc)Error Messages.
* vwarnx: (libc)Error Messages.
* vwprintf: (libc)Variable Arguments Output.
* vwscanf: (libc)Variable Arguments Input.
* wait3: (libc)BSD Wait Functions.
* wait4: (libc)Process Completion.
* wait: (libc)Process Completion.
* waitpid: (libc)Process Completion.
* warn: (libc)Error Messages.
* warnx: (libc)Error Messages.
* wcpcpy: (libc)Copying Strings and Arrays.
* wcpncpy: (libc)Truncating Strings.
* wcrtomb: (libc)Converting a Character.
* wcscasecmp: (libc)String/Array Comparison.
* wcscat: (libc)Concatenating Strings.
* wcschr: (libc)Search Functions.
* wcschrnul: (libc)Search Functions.
* wcscmp: (libc)String/Array Comparison.
* wcscoll: (libc)Collation Functions.
* wcscpy: (libc)Copying Strings and Arrays.
* wcscspn: (libc)Search Functions.
* wcsdup: (libc)Copying Strings and Arrays.
* wcsftime: (libc)Formatting Calendar Time.
* wcslen: (libc)String Length.
* wcsncasecmp: (libc)String/Array Comparison.
* wcsncat: (libc)Truncating Strings.
* wcsncmp: (libc)String/Array Comparison.
* wcsncpy: (libc)Truncating Strings.
* wcsnlen: (libc)String Length.
* wcsnrtombs: (libc)Converting Strings.
* wcspbrk: (libc)Search Functions.
* wcsrchr: (libc)Search Functions.
* wcsrtombs: (libc)Converting Strings.
* wcsspn: (libc)Search Functions.
* wcsstr: (libc)Search Functions.
* wcstod: (libc)Parsing of Floats.
* wcstof: (libc)Parsing of Floats.
* wcstofN: (libc)Parsing of Floats.
* wcstofNx: (libc)Parsing of Floats.
* wcstoimax: (libc)Parsing of Integers.
* wcstok: (libc)Finding Tokens in a String.
* wcstol: (libc)Parsing of Integers.
* wcstold: (libc)Parsing of Floats.
* wcstoll: (libc)Parsing of Integers.
* wcstombs: (libc)Non-reentrant String Conversion.
* wcstoq: (libc)Parsing of Integers.
* wcstoul: (libc)Parsing of Integers.
* wcstoull: (libc)Parsing of Integers.
* wcstoumax: (libc)Parsing of Integers.
* wcstouq: (libc)Parsing of Integers.
* wcswcs: (libc)Search Functions.
* wcsxfrm: (libc)Collation Functions.
* wctob: (libc)Converting a Character.
* wctomb: (libc)Non-reentrant Character Conversion.
* wctrans: (libc)Wide Character Case Conversion.
* wctype: (libc)Classification of Wide Characters.
* wmemchr: (libc)Search Functions.
* wmemcmp: (libc)String/Array Comparison.
* wmemcpy: (libc)Copying Strings and Arrays.
* wmemmove: (libc)Copying Strings and Arrays.
* wmempcpy: (libc)Copying Strings and Arrays.
* wmemset: (libc)Copying Strings and Arrays.
* wordexp: (libc)Calling Wordexp.
* wordfree: (libc)Calling Wordexp.
* wprintf: (libc)Formatted Output Functions.
* write: (libc)I/O Primitives.
* writev: (libc)Scatter-Gather.
* wscanf: (libc)Formatted Input Functions.
* y0: (libc)Special Functions.
* y0f: (libc)Special Functions.
* y0fN: (libc)Special Functions.
* y0fNx: (libc)Special Functions.
* y0l: (libc)Special Functions.
* y1: (libc)Special Functions.
* y1f: (libc)Special Functions.
* y1fN: (libc)Special Functions.
* y1fNx: (libc)Special Functions.
* y1l: (libc)Special Functions.
* yn: (libc)Special Functions.
* ynf: (libc)Special Functions.
* ynfN: (libc)Special Functions.
* ynfNx: (libc)Special Functions.
* ynl: (libc)Special Functions.
END-INFO-DIR-ENTRY


File: libc.info,  Node: Shuffling Bytes,  Next: Obfuscating Data,  Prev: Erasing Sensitive Data,  Up: String and Array Utilities

5.12 Shuffling Bytes
====================

The function below addresses the perennial programming quandary: “How do
I take good data in string form and painlessly turn it into garbage?”
This is not a difficult thing to code for oneself, but the authors of
the GNU C Library wish to make it as convenient as possible.

   To _erase_ data, use ‘explicit_bzero’ (*note Erasing Sensitive
Data::); to obfuscate it reversibly, use ‘memfrob’ (*note Obfuscating
Data::).

 -- Function: char * strfry (char *STRING)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘strfry’ performs an in-place shuffle on STRING.  Each character is
     swapped to a position selected at random, within the portion of the
     string starting with the character’s original position.  (This is
     the Fisher-Yates algorithm for unbiased shuffling.)

     Calling ‘strfry’ will not disturb any of the random number
     generators that have global state (*note Pseudo-Random Numbers::).

     The return value of ‘strfry’ is always STRING.

     *Portability Note:* This function is unique to the GNU C Library.
     It is declared in ‘string.h’.


File: libc.info,  Node: Obfuscating Data,  Next: Encode Binary Data,  Prev: Shuffling Bytes,  Up: String and Array Utilities

5.13 Obfuscating Data
=====================

The ‘memfrob’ function reversibly obfuscates an array of binary data.
This is not true encryption; the obfuscated data still bears a clear
relationship to the original, and no secret key is required to undo the
obfuscation.  It is analogous to the “Rot13” cipher used on Usenet for
obscuring offensive jokes, spoilers for works of fiction, and so on, but
it can be applied to arbitrary binary data.

   Programs that need true encryption—a transformation that completely
obscures the original and cannot be reversed without knowledge of a
secret key—should use a dedicated cryptography library, such as
libgcrypt.

   Programs that need to _destroy_ data should use ‘explicit_bzero’
(*note Erasing Sensitive Data::), or possibly ‘strfry’ (*note Shuffling
Bytes::).

 -- Function: void * memfrob (void *MEM, size_t LENGTH)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The function ‘memfrob’ obfuscates LENGTH bytes of data beginning at
     MEM, in place.  Each byte is bitwise xor-ed with the binary pattern
     00101010 (hexadecimal 0x2A). The return value is always MEM.

     ‘memfrob’ a second time on the same data returns it to its original
     state.

     *Portability Note:* This function is unique to the GNU C Library.
     It is declared in ‘string.h’.


File: libc.info,  Node: Encode Binary Data,  Next: Argz and Envz Vectors,  Prev: Obfuscating Data,  Up: String and Array Utilities

5.14 Encode Binary Data
=======================

To store or transfer binary data in environments which only support text
one has to encode the binary data by mapping the input bytes to bytes in
the range allowed for storing or transferring.  SVID systems (and
nowadays XPG compliant systems) provide minimal support for this task.

 -- Function: char * l64a (long int N)

     Preliminary: | MT-Unsafe race:l64a | AS-Unsafe | AC-Safe | *Note
     POSIX Safety Concepts::.

     This function encodes a 32-bit input value using bytes from the
     basic character set.  It returns a pointer to a 7 byte buffer which
     contains an encoded version of N.  To encode a series of bytes the
     user must copy the returned string to a destination buffer.  It
     returns the empty string if N is zero, which is somewhat bizarre
     but mandated by the standard.
     *Warning:* Since a static buffer is used this function should not
     be used in multi-threaded programs.  There is no thread-safe
     alternative to this function in the C library.
     *Compatibility Note:* The XPG standard states that the return value
     of ‘l64a’ is undefined if N is negative.  In the GNU
     implementation, ‘l64a’ treats its argument as unsigned, so it will
     return a sensible encoding for any nonzero N; however, portable
     programs should not rely on this.

     To encode a large buffer ‘l64a’ must be called in a loop, once for
     each 32-bit word of the buffer.  For example, one could do
     something like this:

          char *
          encode (const void *buf, size_t len)
          {
            /* We know in advance how long the buffer has to be. */
            unsigned char *in = (unsigned char *) buf;
            char *out = malloc (6 + ((len + 3) / 4) * 6 + 1);
            char *cp = out, *p;

            /* Encode the length. */
            /* Using ‘htonl’ is necessary so that the data can be
               decoded even on machines with different byte order.
               ‘l64a’ can return a string shorter than 6 bytes, so
               we pad it with encoding of 0 ('.') at the end by
               hand. */

            p = stpcpy (cp, l64a (htonl (len)));
            cp = mempcpy (p, "......", 6 - (p - cp));

            while (len > 3)
              {
                unsigned long int n = *in++;
                n = (n << 8) | *in++;
                n = (n << 8) | *in++;
                n = (n << 8) | *in++;
                len -= 4;
                p = stpcpy (cp, l64a (htonl (n)));
                cp = mempcpy (p, "......", 6 - (p - cp));
              }
            if (len > 0)
              {
                unsigned long int n = *in++;
                if (--len > 0)
                  {
                    n = (n << 8) | *in++;
                    if (--len > 0)
                      n = (n << 8) | *in;
                  }
                cp = stpcpy (cp, l64a (htonl (n)));
              }
            *cp = '\0';
            return out;
          }

     It is strange that the library does not provide the complete
     functionality needed but so be it.

   To decode data produced with ‘l64a’ the following function should be
used.

 -- Function: long int a64l (const char *STRING)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The parameter STRING should contain a string which was produced by
     a call to ‘l64a’.  The function processes at least 6 bytes of this
     string, and decodes the bytes it finds according to the table
     below.  It stops decoding when it finds a byte not in the table,
     rather like ‘atoi’; if you have a buffer which has been broken into
     lines, you must be careful to skip over the end-of-line bytes.

     The decoded number is returned as a ‘long int’ value.

   The ‘l64a’ and ‘a64l’ functions use a base 64 encoding, in which each
byte of an encoded string represents six bits of an input word.  These
symbols are used for the base 64 digits:

        0     1     2     3     4     5     6     7
0       ‘.’   ‘/’   ‘0’   ‘1’   ‘2’   ‘3’   ‘4’   ‘5’
8       ‘6’   ‘7’   ‘8’   ‘9’   ‘A’   ‘B’   ‘C’   ‘D’
16      ‘E’   ‘F’   ‘G’   ‘H’   ‘I’   ‘J’   ‘K’   ‘L’
24      ‘M’   ‘N’   ‘O’   ‘P’   ‘Q’   ‘R’   ‘S’   ‘T’
32      ‘U’   ‘V’   ‘W’   ‘X’   ‘Y’   ‘Z’   ‘a’   ‘b’
40      ‘c’   ‘d’   ‘e’   ‘f’   ‘g’   ‘h’   ‘i’   ‘j’
48      ‘k’   ‘l’   ‘m’   ‘n’   ‘o’   ‘p’   ‘q’   ‘r’
56      ‘s’   ‘t’   ‘u’   ‘v’   ‘w’   ‘x’   ‘y’   ‘z’

   This encoding scheme is not standard.  There are some other encoding
methods which are much more widely used (UU encoding, MIME encoding).
Generally, it is better to use one of these encodings.


File: libc.info,  Node: Argz and Envz Vectors,  Prev: Encode Binary Data,  Up: String and Array Utilities

5.15 Argz and Envz Vectors
==========================

“argz vectors” are vectors of strings in a contiguous block of memory,
each element separated from its neighbors by null bytes (‘'\0'’).

   “Envz vectors” are an extension of argz vectors where each element is
a name-value pair, separated by a ‘'='’ byte (as in a Unix environment).

* Menu:

* Argz Functions::              Operations on argz vectors.
* Envz Functions::              Additional operations on environment vectors.


File: libc.info,  Node: Argz Functions,  Next: Envz Functions,  Up: Argz and Envz Vectors

5.15.1 Argz Functions
---------------------

Each argz vector is represented by a pointer to the first element, of
type ‘char *’, and a size, of type ‘size_t’, both of which can be
initialized to ‘0’ to represent an empty argz vector.  All argz
functions accept either a pointer and a size argument, or pointers to
them, if they will be modified.

   The argz functions use ‘malloc’/‘realloc’ to allocate/grow argz
vectors, and so any argz vector created using these functions may be
freed by using ‘free’; conversely, any argz function that may grow a
string expects that string to have been allocated using ‘malloc’ (those
argz functions that only examine their arguments or modify them in place
will work on any sort of memory).  *Note Unconstrained Allocation::.

   All argz functions that do memory allocation have a return type of
‘error_t’, and return ‘0’ for success, and ‘ENOMEM’ if an allocation
error occurs.

   These functions are declared in the standard include file ‘argz.h’.

 -- Function: error_t argz_create (char *const ARGV[], char **ARGZ,
          size_t *ARGZ_LEN)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_create’ function converts the Unix-style argument vector
     ARGV (a vector of pointers to normal C strings, terminated by
     ‘(char *)0’; *note Program Arguments::) into an argz vector with
     the same elements, which is returned in ARGZ and ARGZ_LEN.

 -- Function: error_t argz_create_sep (const char *STRING, int SEP, char
          **ARGZ, size_t *ARGZ_LEN)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_create_sep’ function converts the string STRING into an
     argz vector (returned in ARGZ and ARGZ_LEN) by splitting it into
     elements at every occurrence of the byte SEP.

 -- Function: size_t argz_count (const char *ARGZ, size_t ARGZ_LEN)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Returns the number of elements in the argz vector ARGZ and
     ARGZ_LEN.

 -- Function: void argz_extract (const char *ARGZ, size_t ARGZ_LEN, char
          **ARGV)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘argz_extract’ function converts the argz vector ARGZ and
     ARGZ_LEN into a Unix-style argument vector stored in ARGV, by
     putting pointers to every element in ARGZ into successive positions
     in ARGV, followed by a terminator of ‘0’.  ARGV must be
     pre-allocated with enough space to hold all the elements in ARGZ
     plus the terminating ‘(char *)0’ (‘(argz_count (ARGZ, ARGZ_LEN) +
     1) * sizeof (char *)’ bytes should be enough).  Note that the
     string pointers stored into ARGV point into ARGZ—they are not
     copies—and so ARGZ must be copied if it will be changed while ARGV
     is still active.  This function is useful for passing the elements
     in ARGZ to an exec function (*note Executing a File::).

 -- Function: void argz_stringify (char *ARGZ, size_t LEN, int SEP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘argz_stringify’ converts ARGZ into a normal string with the
     elements separated by the byte SEP, by replacing each ‘'\0'’ inside
     ARGZ (except the last one, which terminates the string) with SEP.
     This is handy for printing ARGZ in a readable manner.

 -- Function: error_t argz_add (char **ARGZ, size_t *ARGZ_LEN, const
          char *STR)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_add’ function adds the string STR to the end of the argz
     vector ‘*ARGZ’, and updates ‘*ARGZ’ and ‘*ARGZ_LEN’ accordingly.

 -- Function: error_t argz_add_sep (char **ARGZ, size_t *ARGZ_LEN, const
          char *STR, int DELIM)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_add_sep’ function is similar to ‘argz_add’, but STR is
     split into separate elements in the result at occurrences of the
     byte DELIM.  This is useful, for instance, for adding the
     components of a Unix search path to an argz vector, by using a
     value of ‘':'’ for DELIM.

 -- Function: error_t argz_append (char **ARGZ, size_t *ARGZ_LEN, const
          char *BUF, size_t BUF_LEN)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_append’ function appends BUF_LEN bytes starting at BUF to
     the argz vector ‘*ARGZ’, reallocating ‘*ARGZ’ to accommodate it,
     and adding BUF_LEN to ‘*ARGZ_LEN’.

 -- Function: void argz_delete (char **ARGZ, size_t *ARGZ_LEN, char
          *ENTRY)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     If ENTRY points to the beginning of one of the elements in the argz
     vector ‘*ARGZ’, the ‘argz_delete’ function will remove this entry
     and reallocate ‘*ARGZ’, modifying ‘*ARGZ’ and ‘*ARGZ_LEN’
     accordingly.  Note that as destructive argz functions usually
     reallocate their argz argument, pointers into argz vectors such as
     ENTRY will then become invalid.

 -- Function: error_t argz_insert (char **ARGZ, size_t *ARGZ_LEN, char
          *BEFORE, const char *ENTRY)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘argz_insert’ function inserts the string ENTRY into the argz
     vector ‘*ARGZ’ at a point just before the existing element pointed
     to by BEFORE, reallocating ‘*ARGZ’ and updating ‘*ARGZ’ and
     ‘*ARGZ_LEN’.  If BEFORE is ‘0’, ENTRY is added to the end instead
     (as if by ‘argz_add’).  Since the first element is in fact the same
     as ‘*ARGZ’, passing in ‘*ARGZ’ as the value of BEFORE will result
     in ENTRY being inserted at the beginning.

 -- Function: char * argz_next (const char *ARGZ, size_t ARGZ_LEN, const
          char *ENTRY)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘argz_next’ function provides a convenient way of iterating
     over the elements in the argz vector ARGZ.  It returns a pointer to
     the next element in ARGZ after the element ENTRY, or ‘0’ if there
     are no elements following ENTRY.  If ENTRY is ‘0’, the first
     element of ARGZ is returned.

     This behavior suggests two styles of iteration:

              char *entry = 0;
              while ((entry = argz_next (ARGZ, ARGZ_LEN, entry)))
                ACTION;

     (the double parentheses are necessary to make some C compilers shut
     up about what they consider a questionable ‘while’-test) and:

              char *entry;
              for (entry = ARGZ;
                   entry;
                   entry = argz_next (ARGZ, ARGZ_LEN, entry))
                ACTION;

     Note that the latter depends on ARGZ having a value of ‘0’ if it is
     empty (rather than a pointer to an empty block of memory); this
     invariant is maintained for argz vectors created by the functions
     here.

 -- Function: error_t argz_replace (char **ARGZ, size_t *ARGZ_LEN,
          const char *STR, const char *WITH, unsigned *REPLACE_COUNT)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     Replace any occurrences of the string STR in ARGZ with WITH,
     reallocating ARGZ as necessary.  If REPLACE_COUNT is non-zero,
     ‘*REPLACE_COUNT’ will be incremented by the number of replacements
     performed.


File: libc.info,  Node: Envz Functions,  Prev: Argz Functions,  Up: Argz and Envz Vectors

5.15.2 Envz Functions
---------------------

Envz vectors are just argz vectors with additional constraints on the
form of each element; as such, argz functions can also be used on them,
where it makes sense.

   Each element in an envz vector is a name-value pair, separated by a
‘'='’ byte; if multiple ‘'='’ bytes are present in an element, those
after the first are considered part of the value, and treated like all
other non-‘'\0'’ bytes.

   If _no_ ‘'='’ bytes are present in an element, that element is
considered the name of a “null” entry, as distinct from an entry with an
empty value: ‘envz_get’ will return ‘0’ if given the name of null entry,
whereas an entry with an empty value would result in a value of ‘""’;
‘envz_entry’ will still find such entries, however.  Null entries can be
removed with the ‘envz_strip’ function.

   As with argz functions, envz functions that may allocate memory (and
thus fail) have a return type of ‘error_t’, and return either ‘0’ or
‘ENOMEM’.

   These functions are declared in the standard include file ‘envz.h’.

 -- Function: char * envz_entry (const char *ENVZ, size_t ENVZ_LEN,
          const char *NAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘envz_entry’ function finds the entry in ENVZ with the name
     NAME, and returns a pointer to the whole entry—that is, the argz
     element which begins with NAME followed by a ‘'='’ byte.  If there
     is no entry with that name, ‘0’ is returned.

 -- Function: char * envz_get (const char *ENVZ, size_t ENVZ_LEN, const
          char *NAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘envz_get’ function finds the entry in ENVZ with the name NAME
     (like ‘envz_entry’), and returns a pointer to the value portion of
     that entry (following the ‘'='’).  If there is no entry with that
     name (or only a null entry), ‘0’ is returned.

 -- Function: error_t envz_add (char **ENVZ, size_t *ENVZ_LEN, const
          char *NAME, const char *VALUE)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘envz_add’ function adds an entry to ‘*ENVZ’ (updating ‘*ENVZ’
     and ‘*ENVZ_LEN’) with the name NAME, and value VALUE.  If an entry
     with the same name already exists in ENVZ, it is removed first.  If
     VALUE is ‘0’, then the new entry will be the special null type of
     entry (mentioned above).

 -- Function: error_t envz_merge (char **ENVZ, size_t *ENVZ_LEN, const
          char *ENVZ2, size_t ENVZ2_LEN, int OVERRIDE)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘envz_merge’ function adds each entry in ENVZ2 to ENVZ, as if
     with ‘envz_add’, updating ‘*ENVZ’ and ‘*ENVZ_LEN’.  If OVERRIDE is
     true, then values in ENVZ2 will supersede those with the same name
     in ENVZ, otherwise not.

     Null entries are treated just like other entries in this respect,
     so a null entry in ENVZ can prevent an entry of the same name in
     ENVZ2 from being added to ENVZ, if OVERRIDE is false.

 -- Function: void envz_strip (char **ENVZ, size_t *ENVZ_LEN)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘envz_strip’ function removes any null entries from ENVZ,
     updating ‘*ENVZ’ and ‘*ENVZ_LEN’.

 -- Function: void envz_remove (char **ENVZ, size_t *ENVZ_LEN, const
          char *NAME)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘envz_remove’ function removes an entry named NAME from ENVZ,
     updating ‘*ENVZ’ and ‘*ENVZ_LEN’.


File: libc.info,  Node: Character Set Handling,  Next: Locales,  Prev: String and Array Utilities,  Up: Top

6 Character Set Handling
************************

Character sets used in the early days of computing had only six, seven,
or eight bits for each character: there was never a case where more than
eight bits (one byte) were used to represent a single character.  The
limitations of this approach became more apparent as more people
grappled with non-Roman character sets, where not all the characters
that make up a language’s character set can be represented by 2^8
choices.  This chapter shows the functionality that was added to the C
library to support multiple character sets.

* Menu:

* Extended Char Intro::              Introduction to Extended Characters.
* Charset Function Overview::        Overview about Character Handling
                                      Functions.
* Restartable multibyte conversion:: Restartable multibyte conversion
                                      Functions.
* Non-reentrant Conversion::         Non-reentrant Conversion Function.
* Generic Charset Conversion::       Generic Charset Conversion.


File: libc.info,  Node: Extended Char Intro,  Next: Charset Function Overview,  Up: Character Set Handling

6.1 Introduction to Extended Characters
=======================================

A variety of solutions are available to overcome the differences between
character sets with a 1:1 relation between bytes and characters and
character sets with ratios of 2:1 or 4:1.  The remainder of this section
gives a few examples to help understand the design decisions made while
developing the functionality of the C library.

   A distinction we have to make right away is between internal and
external representation.  “Internal representation” means the
representation used by a program while keeping the text in memory.
External representations are used when text is stored or transmitted
through some communication channel.  Examples of external
representations include files waiting in a directory to be read and
parsed.

   Traditionally there has been no difference between the two
representations.  It was equally comfortable and useful to use the same
single-byte representation internally and externally.  This comfort
level decreases with more and larger character sets.

   One of the problems to overcome with the internal representation is
handling text that is externally encoded using different character sets.
Assume a program that reads two texts and compares them using some
metric.  The comparison can be usefully done only if the texts are
internally kept in a common format.

   For such a common format (= character set) eight bits are certainly
no longer enough.  So the smallest entity will have to grow: “wide
characters” will now be used.  Instead of one byte per character, two or
four will be used instead.  (Three are not good to address in memory and
more than four bytes seem not to be necessary).

   As shown in some other part of this manual, a completely new family
has been created of functions that can handle wide character texts in
memory.  The most commonly used character sets for such internal wide
character representations are Unicode and ISO 10646 (also known as UCS
for Universal Character Set).  Unicode was originally planned as a
16-bit character set; whereas, ISO 10646 was designed to be a 31-bit
large code space.  The two standards are practically identical.  They
have the same character repertoire and code table, but Unicode specifies
added semantics.  At the moment, only characters in the first ‘0x10000’
code positions (the so-called Basic Multilingual Plane, BMP) have been
assigned, but the assignment of more specialized characters outside this
16-bit space is already in progress.  A number of encodings have been
defined for Unicode and ISO 10646 characters: UCS-2 is a 16-bit word
that can only represent characters from the BMP, UCS-4 is a 32-bit word
than can represent any Unicode and ISO 10646 character, UTF-8 is an
ASCII compatible encoding where ASCII characters are represented by
ASCII bytes and non-ASCII characters by sequences of 2-6 non-ASCII
bytes, and finally UTF-16 is an extension of UCS-2 in which pairs of
certain UCS-2 words can be used to encode non-BMP characters up to
‘0x10ffff’.

   To represent wide characters the ‘char’ type is not suitable.  For
this reason the ISO C standard introduces a new type that is designed to
keep one character of a wide character string.  To maintain the
similarity there is also a type corresponding to ‘int’ for those
functions that take a single wide character.

 -- Data type: wchar_t

     This data type is used as the base type for wide character strings.
     In other words, arrays of objects of this type are the equivalent
     of ‘char[]’ for multibyte character strings.  The type is defined
     in ‘stddef.h’.

     The ISO C90 standard, where ‘wchar_t’ was introduced, does not say
     anything specific about the representation.  It only requires that
     this type is capable of storing all elements of the basic character
     set.  Therefore it would be legitimate to define ‘wchar_t’ as
     ‘char’, which might make sense for embedded systems.

     But in the GNU C Library ‘wchar_t’ is always 32 bits wide and,
     therefore, capable of representing all UCS-4 values and, therefore,
     covering all of ISO 10646.  Some Unix systems define ‘wchar_t’ as a
     16-bit type and thereby follow Unicode very strictly.  This
     definition is perfectly fine with the standard, but it also means
     that to represent all characters from Unicode and ISO 10646 one has
     to use UTF-16 surrogate characters, which is in fact a
     multi-wide-character encoding.  But resorting to
     multi-wide-character encoding contradicts the purpose of the
     ‘wchar_t’ type.

 -- Data type: wint_t

     ‘wint_t’ is a data type used for parameters and variables that
     contain a single wide character.  As the name suggests this type is
     the equivalent of ‘int’ when using the normal ‘char’ strings.  The
     types ‘wchar_t’ and ‘wint_t’ often have the same representation if
     their size is 32 bits wide but if ‘wchar_t’ is defined as ‘char’
     the type ‘wint_t’ must be defined as ‘int’ due to the parameter
     promotion.

     This type is defined in ‘wchar.h’ and was introduced in Amendment 1
     to ISO C90.

   As there are for the ‘char’ data type macros are available for
specifying the minimum and maximum value representable in an object of
type ‘wchar_t’.

 -- Macro: wint_t WCHAR_MIN

     The macro ‘WCHAR_MIN’ evaluates to the minimum value representable
     by an object of type ‘wint_t’.

     This macro was introduced in Amendment 1 to ISO C90.

 -- Macro: wint_t WCHAR_MAX

     The macro ‘WCHAR_MAX’ evaluates to the maximum value representable
     by an object of type ‘wint_t’.

     This macro was introduced in Amendment 1 to ISO C90.

   Another special wide character value is the equivalent to ‘EOF’.

 -- Macro: wint_t WEOF

     The macro ‘WEOF’ evaluates to a constant expression of type
     ‘wint_t’ whose value is different from any member of the extended
     character set.

     ‘WEOF’ need not be the same value as ‘EOF’ and unlike ‘EOF’ it also
     need _not_ be negative.  In other words, sloppy code like

          {
            int c;
            ...
            while ((c = getc (fp)) < 0)
              ...
          }

     has to be rewritten to use ‘WEOF’ explicitly when wide characters
     are used:

          {
            wint_t c;
            ...
            while ((c = getwc (fp)) != WEOF)
              ...
          }

     This macro was introduced in Amendment 1 to ISO C90 and is defined
     in ‘wchar.h’.

   These internal representations present problems when it comes to
storage and transmittal.  Because each single wide character consists of
more than one byte, they are affected by byte-ordering.  Thus, machines
with different endianesses would see different values when accessing the
same data.  This byte ordering concern also applies for communication
protocols that are all byte-based and therefore require that the sender
has to decide about splitting the wide character in bytes.  A last (but
not least important) point is that wide characters often require more
storage space than a customized byte-oriented character set.

   For all the above reasons, an external encoding that is different
from the internal encoding is often used if the latter is UCS-2 or
UCS-4.  The external encoding is byte-based and can be chosen
appropriately for the environment and for the texts to be handled.  A
variety of different character sets can be used for this external
encoding (information that will not be exhaustively presented
here–instead, a description of the major groups will suffice).  All of
the ASCII-based character sets fulfill one requirement: they are
"filesystem safe."  This means that the character ‘'/'’ is used in the
encoding _only_ to represent itself.  Things are a bit different for
character sets like EBCDIC (Extended Binary Coded Decimal Interchange
Code, a character set family used by IBM), but if the operating system
does not understand EBCDIC directly the parameters-to-system calls have
to be converted first anyhow.

   • The simplest character sets are single-byte character sets.  There
     can be only up to 256 characters (for 8 bit character sets), which
     is not sufficient to cover all languages but might be sufficient to
     handle a specific text.  Handling of a 8 bit character sets is
     simple.  This is not true for other kinds presented later, and
     therefore, the application one uses might require the use of 8 bit
     character sets.

   • The ISO 2022 standard defines a mechanism for extended character
     sets where one character _can_ be represented by more than one
     byte.  This is achieved by associating a state with the text.
     Characters that can be used to change the state can be embedded in
     the text.  Each byte in the text might have a different
     interpretation in each state.  The state might even influence
     whether a given byte stands for a character on its own or whether
     it has to be combined with some more bytes.

     In most uses of ISO 2022 the defined character sets do not allow
     state changes that cover more than the next character.  This has
     the big advantage that whenever one can identify the beginning of
     the byte sequence of a character one can interpret a text
     correctly.  Examples of character sets using this policy are the
     various EUC character sets (used by Sun’s operating systems,
     EUC-JP, EUC-KR, EUC-TW, and EUC-CN) or Shift_JIS (SJIS, a Japanese
     encoding).

     But there are also character sets using a state that is valid for
     more than one character and has to be changed by another byte
     sequence.  Examples for this are ISO-2022-JP, ISO-2022-KR, and
     ISO-2022-CN.

   • Early attempts to fix 8 bit character sets for other languages
     using the Roman alphabet lead to character sets like ISO 6937.
     Here bytes representing characters like the acute accent do not
     produce output themselves: one has to combine them with other
     characters to get the desired result.  For example, the byte
     sequence ‘0xc2 0x61’ (non-spacing acute accent, followed by
     lower-case ‘a’) to get the “small a with acute” character.  To get
     the acute accent character on its own, one has to write ‘0xc2 0x20’
     (the non-spacing acute followed by a space).

     Character sets like ISO 6937 are used in some embedded systems such
     as teletex.

   • Instead of converting the Unicode or ISO 10646 text used
     internally, it is often also sufficient to simply use an encoding
     different than UCS-2/UCS-4.  The Unicode and ISO 10646 standards
     even specify such an encoding: UTF-8.  This encoding is able to
     represent all of ISO 10646 31 bits in a byte string of length one
     to six.

     There were a few other attempts to encode ISO 10646 such as UTF-7,
     but UTF-8 is today the only encoding that should be used.  In fact,
     with any luck UTF-8 will soon be the only external encoding that
     has to be supported.  It proves to be universally usable and its
     only disadvantage is that it favors Roman languages by making the
     byte string representation of other scripts (Cyrillic, Greek, Asian
     scripts) longer than necessary if using a specific character set
     for these scripts.  Methods like the Unicode compression scheme can
     alleviate these problems.

   The question remaining is: how to select the character set or
encoding to use.  The answer: you cannot decide about it yourself, it is
decided by the developers of the system or the majority of the users.
Since the goal is interoperability one has to use whatever the other
people one works with use.  If there are no constraints, the selection
is based on the requirements the expected circle of users will have.  In
other words, if a project is expected to be used in only, say, Russia it
is fine to use KOI8-R or a similar character set.  But if at the same
time people from, say, Greece are participating one should use a
character set that allows all people to collaborate.

   The most widely useful solution seems to be: go with the most general
character set, namely ISO 10646.  Use UTF-8 as the external encoding and
problems about users not being able to use their own language adequately
are a thing of the past.

   One final comment about the choice of the wide character
representation is necessary at this point.  We have said above that the
natural choice is using Unicode or ISO 10646.  This is not required, but
at least encouraged, by the ISO C standard.  The standard defines at
least a macro ‘__STDC_ISO_10646__’ that is only defined on systems where
the ‘wchar_t’ type encodes ISO 10646 characters.  If this symbol is not
defined one should avoid making assumptions about the wide character
representation.  If the programmer uses only the functions provided by
the C library to handle wide character strings there should be no
compatibility problems with other systems.


File: libc.info,  Node: Charset Function Overview,  Next: Restartable multibyte conversion,  Prev: Extended Char Intro,  Up: Character Set Handling

6.2 Overview about Character Handling Functions
===============================================

A Unix C library contains three different sets of functions in two
families to handle character set conversion.  One of the function
families (the most commonly used) is specified in the ISO C90 standard
and, therefore, is portable even beyond the Unix world.  Unfortunately
this family is the least useful one.  These functions should be avoided
whenever possible, especially when developing libraries (as opposed to
applications).

   The second family of functions got introduced in the early Unix
standards (XPG2) and is still part of the latest and greatest Unix
standard: Unix 98.  It is also the most powerful and useful set of
functions.  But we will start with the functions defined in Amendment 1
to ISO C90.


File: libc.info,  Node: Restartable multibyte conversion,  Next: Non-reentrant Conversion,  Prev: Charset Function Overview,  Up: Character Set Handling

6.3 Restartable Multibyte Conversion Functions
==============================================

The ISO C standard defines functions to convert strings from a multibyte
representation to wide character strings.  There are a number of
peculiarities:

   • The character set assumed for the multibyte encoding is not
     specified as an argument to the functions.  Instead the character
     set specified by the ‘LC_CTYPE’ category of the current locale is
     used; see *note Locale Categories::.

   • The functions handling more than one character at a time require
     NUL terminated strings as the argument (i.e., converting blocks of
     text does not work unless one can add a NUL byte at an appropriate
     place).  The GNU C Library contains some extensions to the standard
     that allow specifying a size, but basically they also expect
     terminated strings.

   Despite these limitations the ISO C functions can be used in many
contexts.  In graphical user interfaces, for instance, it is not
uncommon to have functions that require text to be displayed in a wide
character string if the text is not simple ASCII. The text itself might
come from a file with translations and the user should decide about the
current locale, which determines the translation and therefore also the
external encoding used.  In such a situation (and many others) the
functions described here are perfect.  If more freedom while performing
the conversion is necessary take a look at the ‘iconv’ functions (*note
Generic Charset Conversion::).

* Menu:

* Selecting the Conversion::     Selecting the conversion and its properties.
* Keeping the state::            Representing the state of the conversion.
* Converting a Character::       Converting Single Characters.
* Converting Strings::           Converting Multibyte and Wide Character
                                  Strings.
* Multibyte Conversion Example:: A Complete Multibyte Conversion Example.


File: libc.info,  Node: Selecting the Conversion,  Next: Keeping the state,  Up: Restartable multibyte conversion

6.3.1 Selecting the conversion and its properties
-------------------------------------------------

We already said above that the currently selected locale for the
‘LC_CTYPE’ category decides the conversion that is performed by the
functions we are about to describe.  Each locale uses its own character
set (given as an argument to ‘localedef’) and this is the one assumed as
the external multibyte encoding.  The wide character set is always UCS-4
in the GNU C Library.

   A characteristic of each multibyte character set is the maximum
number of bytes that can be necessary to represent one character.  This
information is quite important when writing code that uses the
conversion functions (as shown in the examples below).  The ISO C
standard defines two macros that provide this information.

 -- Macro: int MB_LEN_MAX

     ‘MB_LEN_MAX’ specifies the maximum number of bytes in the multibyte
     sequence for a single character in any of the supported locales.
     It is a compile-time constant and is defined in ‘limits.h’.

 -- Macro: int MB_CUR_MAX

     ‘MB_CUR_MAX’ expands into a positive integer expression that is the
     maximum number of bytes in a multibyte character in the current
     locale.  The value is never greater than ‘MB_LEN_MAX’.  Unlike
     ‘MB_LEN_MAX’ this macro need not be a compile-time constant, and in
     the GNU C Library it is not.

     ‘MB_CUR_MAX’ is defined in ‘stdlib.h’.

   Two different macros are necessary since strictly ISO C90 compilers
do not allow variable length array definitions, but still it is
desirable to avoid dynamic allocation.  This incomplete piece of code
shows the problem:

     {
       char buf[MB_LEN_MAX];
       ssize_t len = 0;

       while (! feof (fp))
         {
           fread (&buf[len], 1, MB_CUR_MAX - len, fp);
           /* ... process buf */
           len -= used;
         }
     }

   The code in the inner loop is expected to have always enough bytes in
the array BUF to convert one multibyte character.  The array BUF has to
be sized statically since many compilers do not allow a variable size.
The ‘fread’ call makes sure that ‘MB_CUR_MAX’ bytes are always available
in BUF.  Note that it isn’t a problem if ‘MB_CUR_MAX’ is not a
compile-time constant.


File: libc.info,  Node: Keeping the state,  Next: Converting a Character,  Prev: Selecting the Conversion,  Up: Restartable multibyte conversion

6.3.2 Representing the state of the conversion
----------------------------------------------

In the introduction of this chapter it was said that certain character
sets use a “stateful” encoding.  That is, the encoded values depend in
some way on the previous bytes in the text.

   Since the conversion functions allow converting a text in more than
one step we must have a way to pass this information from one call of
the functions to another.

 -- Data type: mbstate_t

     A variable of type ‘mbstate_t’ can contain all the information
     about the “shift state” needed from one call to a conversion
     function to another.

     ‘mbstate_t’ is defined in ‘wchar.h’.  It was introduced in
     Amendment 1 to ISO C90.

   To use objects of type ‘mbstate_t’ the programmer has to define such
objects (normally as local variables on the stack) and pass a pointer to
the object to the conversion functions.  This way the conversion
function can update the object if the current multibyte character set is
stateful.

   There is no specific function or initializer to put the state object
in any specific state.  The rules are that the object should always
represent the initial state before the first use, and this is achieved
by clearing the whole variable with code such as follows:

     {
       mbstate_t state;
       memset (&state, '\0', sizeof (state));
       /* from now on STATE can be used.  */
       ...
     }

   When using the conversion functions to generate output it is often
necessary to test whether the current state corresponds to the initial
state.  This is necessary, for example, to decide whether to emit escape
sequences to set the state to the initial state at certain sequence
points.  Communication protocols often require this.

 -- Function: int mbsinit (const mbstate_t *PS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘mbsinit’ function determines whether the state object pointed
     to by PS is in the initial state.  If PS is a null pointer or the
     object is in the initial state the return value is nonzero.
     Otherwise it is zero.

     ‘mbsinit’ was introduced in Amendment 1 to ISO C90 and is declared
     in ‘wchar.h’.

   Code using ‘mbsinit’ often looks similar to this:

     {
       mbstate_t state;
       memset (&state, '\0', sizeof (state));
       /* Use STATE.  */
       ...
       if (! mbsinit (&state))
         {
           /* Emit code to return to initial state.  */
           const wchar_t empty[] = L"";
           const wchar_t *srcp = empty;
           wcsrtombs (outbuf, &srcp, outbuflen, &state);
         }
       ...
     }

   The code to emit the escape sequence to get back to the initial state
is interesting.  The ‘wcsrtombs’ function can be used to determine the
necessary output code (*note Converting Strings::).  Please note that
with the GNU C Library it is not necessary to perform this extra action
for the conversion from multibyte text to wide character text since the
wide character encoding is not stateful.  But there is nothing mentioned
in any standard that prohibits making ‘wchar_t’ use a stateful encoding.


File: libc.info,  Node: Converting a Character,  Next: Converting Strings,  Prev: Keeping the state,  Up: Restartable multibyte conversion

6.3.3 Converting Single Characters
----------------------------------

The most fundamental of the conversion functions are those dealing with
single characters.  Please note that this does not always mean single
bytes.  But since there is very often a subset of the multibyte
character set that consists of single byte sequences, there are
functions to help with converting bytes.  Frequently, ASCII is a subset
of the multibyte character set.  In such a scenario, each ASCII
character stands for itself, and all other characters have at least a
first byte that is beyond the range 0 to 127.

 -- Function: wint_t btowc (int C)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘btowc’ function (“byte to wide character”) converts a valid
     single byte character C in the initial shift state into the wide
     character equivalent using the conversion rules from the currently
     selected locale of the ‘LC_CTYPE’ category.

     If ‘(unsigned char) C’ is no valid single byte multibyte character
     or if C is ‘EOF’, the function returns ‘WEOF’.

     Please note the restriction of C being tested for validity only in
     the initial shift state.  No ‘mbstate_t’ object is used from which
     the state information is taken, and the function also does not use
     any static state.

     The ‘btowc’ function was introduced in Amendment 1 to ISO C90 and
     is declared in ‘wchar.h’.

   Despite the limitation that the single byte value is always
interpreted in the initial state, this function is actually useful most
of the time.  Most characters are either entirely single-byte character
sets or they are extensions to ASCII. But then it is possible to write
code like this (not that this specific example is very useful):

     wchar_t *
     itow (unsigned long int val)
     {
       static wchar_t buf[30];
       wchar_t *wcp = &buf[29];
       *wcp = L'\0';
       while (val != 0)
         {
           *--wcp = btowc ('0' + val % 10);
           val /= 10;
         }
       if (wcp == &buf[29])
         *--wcp = L'0';
       return wcp;
     }

   Why is it necessary to use such a complicated implementation and not
simply cast ‘'0' + val % 10’ to a wide character?  The answer is that
there is no guarantee that one can perform this kind of arithmetic on
the character of the character set used for ‘wchar_t’ representation.
In other situations the bytes are not constant at compile time and so
the compiler cannot do the work.  In situations like this, using ‘btowc’
is required.

There is also a function for the conversion in the other direction.

 -- Function: int wctob (wint_t C)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘wctob’ function (“wide character to byte”) takes as the
     parameter a valid wide character.  If the multibyte representation
     for this character in the initial state is exactly one byte long,
     the return value of this function is this character.  Otherwise the
     return value is ‘EOF’.

     ‘wctob’ was introduced in Amendment 1 to ISO C90 and is declared in
     ‘wchar.h’.

   There are more general functions to convert single characters from
multibyte representation to wide characters and vice versa.  These
functions pose no limit on the length of the multibyte representation
and they also do not require it to be in the initial state.

 -- Function: size_t mbrtowc (wchar_t *restrict PWC, const char
          *restrict S, size_t N, mbstate_t *restrict PS)

     Preliminary: | MT-Unsafe race:mbrtowc/!ps | AS-Unsafe corrupt heap
     lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety
     Concepts::.

     The ‘mbrtowc’ function (“multibyte restartable to wide character”)
     converts the next multibyte character in the string pointed to by S
     into a wide character and stores it in the location pointed to by
     PWC.  The conversion is performed according to the locale currently
     selected for the ‘LC_CTYPE’ category.  If the conversion for the
     character set used in the locale requires a state, the multibyte
     string is interpreted in the state represented by the object
     pointed to by PS.  If PS is a null pointer, a static, internal
     state variable used only by the ‘mbrtowc’ function is used.

     If the next multibyte character corresponds to the null wide
     character, the return value of the function is 0 and the state
     object is afterwards in the initial state.  If the next N or fewer
     bytes form a correct multibyte character, the return value is the
     number of bytes starting from S that form the multibyte character.
     The conversion state is updated according to the bytes consumed in
     the conversion.  In both cases the wide character (either the
     ‘L'\0'’ or the one found in the conversion) is stored in the string
     pointed to by PWC if PWC is not null.

     If the first N bytes of the multibyte string possibly form a valid
     multibyte character but there are more than N bytes needed to
     complete it, the return value of the function is ‘(size_t) -2’ and
     no value is stored in ‘*PWC’.  The conversion state is updated and
     all N input bytes are consumed and should not be submitted again.
     Please note that this can happen even if N has a value greater than
     or equal to ‘MB_CUR_MAX’ since the input might contain redundant
     shift sequences.

     If the first ‘n’ bytes of the multibyte string cannot possibly form
     a valid multibyte character, no value is stored, the global
     variable ‘errno’ is set to the value ‘EILSEQ’, and the function
     returns ‘(size_t) -1’.  The conversion state is afterwards
     undefined.

     As specified, the ‘mbrtowc’ function could deal with multibyte
     sequences which contain embedded null bytes (which happens in
     Unicode encodings such as UTF-16), but the GNU C Library does not
     support such multibyte encodings.  When encountering a null input
     byte, the function will either return zero, or return ‘(size_t)
     -1)’ and report a ‘EILSEQ’ error.  The ‘iconv’ function can be used
     for converting between arbitrary encodings.  *Note Generic
     Conversion Interface::.

     ‘mbrtowc’ was introduced in Amendment 1 to ISO C90 and is declared
     in ‘wchar.h’.

   A function that copies a multibyte string into a wide character
string while at the same time converting all lowercase characters into
uppercase could look like this:

     wchar_t *
     mbstouwcs (const char *s)
     {
       /* Include the null terminator in the conversion. */
       size_t len = strlen (s) + 1;
       wchar_t *result = reallocarray (NULL, len, sizeof (wchar_t));
       if (result == NULL)
         return NULL;

       wchar_t *wcp = result;
       mbstate_t state;
       memset (&state, '\0', sizeof (state));

       while (true)
         {
           wchar_t wc;
           size_t nbytes = mbrtowc (&wc, s, len, &state);
           if (nbytes == 0)
             {
               /* Terminate the result string. */
               *wcp = L'\0';
               break;
             }
           else if (nbytes == (size_t) -2)
             {
               /* Truncated input string. */
               errno = EILSEQ;
               free (result);
               return NULL;
             }
           else if (nbytes == (size_t) -1)
             {
               /* Some other error (including EILSEQ). */
               free (result);
               return NULL;
             }
           else
             {
               /* A character was converted. */
               *wcp++ = towupper (wc);
               len -= nbytes;
               s += nbytes;
             }
         }
       return result;
     }

   In the inner loop, a single wide character is stored in ‘wc’, and the
number of consumed bytes is stored in the variable ‘nbytes’.  If the
conversion is successful, the uppercase variant of the wide character is
stored in the ‘result’ array and the pointer to the input string and the
number of available bytes is adjusted.  If the ‘mbrtowc’ function
returns zero, the null input byte has not been converted, so it must be
stored explicitly in the result.

   The above code uses the fact that there can never be more wide
characters in the converted result than there are bytes in the multibyte
input string.  This method yields a pessimistic guess about the size of
the result, and if many wide character strings have to be constructed
this way or if the strings are long, the extra memory required to be
allocated because the input string contains multibyte characters might
be significant.  The allocated memory block can be resized to the
correct size before returning it, but a better solution might be to
allocate just the right amount of space for the result right away.
Unfortunately there is no function to compute the length of the wide
character string directly from the multibyte string.  There is, however,
a function that does part of the work.

 -- Function: size_t mbrlen (const char *restrict S, size_t N, mbstate_t
          *PS)

     Preliminary: | MT-Unsafe race:mbrlen/!ps | AS-Unsafe corrupt heap
     lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety
     Concepts::.

     The ‘mbrlen’ function (“multibyte restartable length”) computes the
     number of at most N bytes starting at S, which form the next valid
     and complete multibyte character.

     If the next multibyte character corresponds to the NUL wide
     character, the return value is 0.  If the next N bytes form a valid
     multibyte character, the number of bytes belonging to this
     multibyte character byte sequence is returned.

     If the first N bytes possibly form a valid multibyte character but
     the character is incomplete, the return value is ‘(size_t) -2’.
     Otherwise the multibyte character sequence is invalid and the
     return value is ‘(size_t) -1’.

     The multibyte sequence is interpreted in the state represented by
     the object pointed to by PS.  If PS is a null pointer, a state
     object local to ‘mbrlen’ is used.

     ‘mbrlen’ was introduced in Amendment 1 to ISO C90 and is declared
     in ‘wchar.h’.

   The attentive reader now will note that ‘mbrlen’ can be implemented
as

     mbrtowc (NULL, s, n, ps != NULL ? ps : &internal)

   This is true and in fact is mentioned in the official specification.
How can this function be used to determine the length of the wide
character string created from a multibyte character string?  It is not
directly usable, but we can define a function ‘mbslen’ using it:

     size_t
     mbslen (const char *s)
     {
       mbstate_t state;
       size_t result = 0;
       size_t nbytes;
       memset (&state, '\0', sizeof (state));
       while ((nbytes = mbrlen (s, MB_LEN_MAX, &state)) > 0)
         {
           if (nbytes >= (size_t) -2)
             /* Something is wrong.  */
             return (size_t) -1;
           s += nbytes;
           ++result;
         }
       return result;
     }

   This function simply calls ‘mbrlen’ for each multibyte character in
the string and counts the number of function calls.  Please note that we
here use ‘MB_LEN_MAX’ as the size argument in the ‘mbrlen’ call.  This
is acceptable since a) this value is larger than the length of the
longest multibyte character sequence and b) we know that the string S
ends with a NUL byte, which cannot be part of any other multibyte
character sequence but the one representing the NUL wide character.
Therefore, the ‘mbrlen’ function will never read invalid memory.

   Now that this function is available (just to make this clear, this
function is _not_ part of the GNU C Library) we can compute the number
of wide characters required to store the converted multibyte character
string S using

     wcs_bytes = (mbslen (s) + 1) * sizeof (wchar_t);

   Please note that the ‘mbslen’ function is quite inefficient.  The
implementation of ‘mbstouwcs’ with ‘mbslen’ would have to perform the
conversion of the multibyte character input string twice, and this
conversion might be quite expensive.  So it is necessary to think about
the consequences of using the easier but imprecise method before doing
the work twice.

 -- Function: size_t wcrtomb (char *restrict S, wchar_t WC, mbstate_t
          *restrict PS)

     Preliminary: | MT-Unsafe race:wcrtomb/!ps | AS-Unsafe corrupt heap
     lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety
     Concepts::.

     The ‘wcrtomb’ function (“wide character restartable to multibyte”)
     converts a single wide character into a multibyte string
     corresponding to that wide character.

     If S is a null pointer, the function resets the state stored in the
     object pointed to by PS (or the internal ‘mbstate_t’ object) to the
     initial state.  This can also be achieved by a call like this:

          wcrtombs (temp_buf, L'\0', ps)

     since, if S is a null pointer, ‘wcrtomb’ performs as if it writes
     into an internal buffer, which is guaranteed to be large enough.

     If WC is the NUL wide character, ‘wcrtomb’ emits, if necessary, a
     shift sequence to get the state PS into the initial state followed
     by a single NUL byte, which is stored in the string S.

     Otherwise a byte sequence (possibly including shift sequences) is
     written into the string S.  This only happens if WC is a valid wide
     character (i.e., it has a multibyte representation in the character
     set selected by locale of the ‘LC_CTYPE’ category).  If WC is no
     valid wide character, nothing is stored in the strings S, ‘errno’
     is set to ‘EILSEQ’, the conversion state in PS is undefined and the
     return value is ‘(size_t) -1’.

     If no error occurred the function returns the number of bytes
     stored in the string S.  This includes all bytes representing shift
     sequences.

     One word about the interface of the function: there is no parameter
     specifying the length of the array S.  Instead the function assumes
     that there are at least ‘MB_CUR_MAX’ bytes available since this is
     the maximum length of any byte sequence representing a single
     character.  So the caller has to make sure that there is enough
     space available, otherwise buffer overruns can occur.

     ‘wcrtomb’ was introduced in Amendment 1 to ISO C90 and is declared
     in ‘wchar.h’.

   Using ‘wcrtomb’ is as easy as using ‘mbrtowc’.  The following example
appends a wide character string to a multibyte character string.  Again,
the code is not really useful (or correct), it is simply here to
demonstrate the use and some problems.

     char *
     mbscatwcs (char *s, size_t len, const wchar_t *ws)
     {
       mbstate_t state;
       /* Find the end of the existing string.  */
       char *wp = strchr (s, '\0');
       len -= wp - s;
       memset (&state, '\0', sizeof (state));
       do
         {
           size_t nbytes;
           if (len < MB_CUR_LEN)
             {
               /* We cannot guarantee that the next
                  character fits into the buffer, so
                  return an error.  */
               errno = E2BIG;
               return NULL;
             }
           nbytes = wcrtomb (wp, *ws, &state);
           if (nbytes == (size_t) -1)
             /* Error in the conversion.  */
             return NULL;
           len -= nbytes;
           wp += nbytes;
         }
       while (*ws++ != L'\0');
       return s;
     }

   First the function has to find the end of the string currently in the
array S.  The ‘strchr’ call does this very efficiently since a
requirement for multibyte character representations is that the NUL byte
is never used except to represent itself (and in this context, the end
of the string).

   After initializing the state object the loop is entered where the
first task is to make sure there is enough room in the array S.  We
abort if there are not at least ‘MB_CUR_LEN’ bytes available.  This is
not always optimal but we have no other choice.  We might have less than
‘MB_CUR_LEN’ bytes available but the next multibyte character might also
be only one byte long.  At the time the ‘wcrtomb’ call returns it is too
late to decide whether the buffer was large enough.  If this solution is
unsuitable, there is a very slow but more accurate solution.

       ...
       if (len < MB_CUR_LEN)
         {
           mbstate_t temp_state;
           memcpy (&temp_state, &state, sizeof (state));
           if (wcrtomb (NULL, *ws, &temp_state) > len)
             {
               /* We cannot guarantee that the next
                  character fits into the buffer, so
                  return an error.  */
               errno = E2BIG;
               return NULL;
             }
         }
       ...

   Here we perform the conversion that might overflow the buffer so that
we are afterwards in the position to make an exact decision about the
buffer size.  Please note the ‘NULL’ argument for the destination buffer
in the new ‘wcrtomb’ call; since we are not interested in the converted
text at this point, this is a nice way to express this.  The most
unusual thing about this piece of code certainly is the duplication of
the conversion state object, but if a change of the state is necessary
to emit the next multibyte character, we want to have the same shift
state change performed in the real conversion.  Therefore, we have to
preserve the initial shift state information.

   There are certainly many more and even better solutions to this
problem.  This example is only provided for educational purposes.


File: libc.info,  Node: Converting Strings,  Next: Multibyte Conversion Example,  Prev: Converting a Character,  Up: Restartable multibyte conversion

6.3.4 Converting Multibyte and Wide Character Strings
-----------------------------------------------------

The functions described in the previous section only convert a single
character at a time.  Most operations to be performed in real-world
programs include strings and therefore the ISO C standard also defines
conversions on entire strings.  However, the defined set of functions is
quite limited; therefore, the GNU C Library contains a few extensions
that can help in some important situations.

 -- Function: size_t mbsrtowcs (wchar_t *restrict DST, const char
          **restrict SRC, size_t LEN, mbstate_t *restrict PS)

     Preliminary: | MT-Unsafe race:mbsrtowcs/!ps | AS-Unsafe corrupt
     heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX
     Safety Concepts::.

     The ‘mbsrtowcs’ function (“multibyte string restartable to wide
     character string”) converts the NUL-terminated multibyte character
     string at ‘*SRC’ into an equivalent wide character string,
     including the NUL wide character at the end.  The conversion is
     started using the state information from the object pointed to by
     PS or from an internal object of ‘mbsrtowcs’ if PS is a null
     pointer.  Before returning, the state object is updated to match
     the state after the last converted character.  The state is the
     initial state if the terminating NUL byte is reached and converted.

     If DST is not a null pointer, the result is stored in the array
     pointed to by DST; otherwise, the conversion result is not
     available since it is stored in an internal buffer.

     If LEN wide characters are stored in the array DST before reaching
     the end of the input string, the conversion stops and LEN is
     returned.  If DST is a null pointer, LEN is never checked.

     Another reason for a premature return from the function call is if
     the input string contains an invalid multibyte sequence.  In this
     case the global variable ‘errno’ is set to ‘EILSEQ’ and the
     function returns ‘(size_t) -1’.

     In all other cases the function returns the number of wide
     characters converted during this call.  If DST is not null,
     ‘mbsrtowcs’ stores in the pointer pointed to by SRC either a null
     pointer (if the NUL byte in the input string was reached) or the
     address of the byte following the last converted multibyte
     character.

     Like ‘mbstowcs’ the DST parameter may be a null pointer and the
     function can be used to count the number of wide characters that
     would be required.

     ‘mbsrtowcs’ was introduced in Amendment 1 to ISO C90 and is
     declared in ‘wchar.h’.

   The definition of the ‘mbsrtowcs’ function has one important
limitation.  The requirement that DST has to be a NUL-terminated string
provides problems if one wants to convert buffers with text.  A buffer
is not normally a collection of NUL-terminated strings but instead a
continuous collection of lines, separated by newline characters.  Now
assume that a function to convert one line from a buffer is needed.
Since the line is not NUL-terminated, the source pointer cannot directly
point into the unmodified text buffer.  This means, either one inserts
the NUL byte at the appropriate place for the time of the ‘mbsrtowcs’
function call (which is not doable for a read-only buffer or in a
multi-threaded application) or one copies the line in an extra buffer
where it can be terminated by a NUL byte.  Note that it is not in
general possible to limit the number of characters to convert by setting
the parameter LEN to any specific value.  Since it is not known how many
bytes each multibyte character sequence is in length, one can only
guess.

   There is still a problem with the method of NUL-terminating a line
right after the newline character, which could lead to very strange
results.  As said in the description of the ‘mbsrtowcs’ function above,
the conversion state is guaranteed to be in the initial shift state
after processing the NUL byte at the end of the input string.  But this
NUL byte is not really part of the text (i.e., the conversion state
after the newline in the original text could be something different than
the initial shift state and therefore the first character of the next
line is encoded using this state).  But the state in question is never
accessible to the user since the conversion stops after the NUL byte
(which resets the state).  Most stateful character sets in use today
require that the shift state after a newline be the initial state–but
this is not a strict guarantee.  Therefore, simply NUL-terminating a
piece of a running text is not always an adequate solution and,
therefore, should never be used in generally used code.

   The generic conversion interface (*note Generic Charset Conversion::)
does not have this limitation (it simply works on buffers, not strings),
and the GNU C Library contains a set of functions that take additional
parameters specifying the maximal number of bytes that are consumed from
the input string.  This way the problem of ‘mbsrtowcs’’s example above
could be solved by determining the line length and passing this length
to the function.

 -- Function: size_t wcsrtombs (char *restrict DST, const wchar_t
          **restrict SRC, size_t LEN, mbstate_t *restrict PS)

     Preliminary: | MT-Unsafe race:wcsrtombs/!ps | AS-Unsafe corrupt
     heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX
     Safety Concepts::.

     The ‘wcsrtombs’ function (“wide character string restartable to
     multibyte string”) converts the NUL-terminated wide character
     string at ‘*SRC’ into an equivalent multibyte character string and
     stores the result in the array pointed to by DST.  The NUL wide
     character is also converted.  The conversion starts in the state
     described in the object pointed to by PS or by a state object local
     to ‘wcsrtombs’ in case PS is a null pointer.  If DST is a null
     pointer, the conversion is performed as usual but the result is not
     available.  If all characters of the input string were successfully
     converted and if DST is not a null pointer, the pointer pointed to
     by SRC gets assigned a null pointer.

     If one of the wide characters in the input string has no valid
     multibyte character equivalent, the conversion stops early, sets
     the global variable ‘errno’ to ‘EILSEQ’, and returns ‘(size_t) -1’.

     Another reason for a premature stop is if DST is not a null pointer
     and the next converted character would require more than LEN bytes
     in total to the array DST.  In this case (and if DST is not a null
     pointer) the pointer pointed to by SRC is assigned a value pointing
     to the wide character right after the last one successfully
     converted.

     Except in the case of an encoding error the return value of the
     ‘wcsrtombs’ function is the number of bytes in all the multibyte
     character sequences which were or would have been (if DST was not a
     null) stored in DST.  Before returning, the state in the object
     pointed to by PS (or the internal object in case PS is a null
     pointer) is updated to reflect the state after the last conversion.
     The state is the initial shift state in case the terminating NUL
     wide character was converted.

     The ‘wcsrtombs’ function was introduced in Amendment 1 to ISO C90
     and is declared in ‘wchar.h’.

   The restriction mentioned above for the ‘mbsrtowcs’ function applies
here also.  There is no possibility of directly controlling the number
of input characters.  One has to place the NUL wide character at the
correct place or control the consumed input indirectly via the available
output array size (the LEN parameter).

 -- Function: size_t mbsnrtowcs (wchar_t *restrict DST, const char
          **restrict SRC, size_t NMC, size_t LEN, mbstate_t *restrict
          PS)

     Preliminary: | MT-Unsafe race:mbsnrtowcs/!ps | AS-Unsafe corrupt
     heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX
     Safety Concepts::.

     The ‘mbsnrtowcs’ function is very similar to the ‘mbsrtowcs’
     function.  All the parameters are the same except for NMC, which is
     new.  The return value is the same as for ‘mbsrtowcs’.

     This new parameter specifies how many bytes at most can be used
     from the multibyte character string.  In other words, the multibyte
     character string ‘*SRC’ need not be NUL-terminated.  But if a NUL
     byte is found within the NMC first bytes of the string, the
     conversion stops there.

     Like ‘mbstowcs’ the DST parameter may be a null pointer and the
     function can be used to count the number of wide characters that
     would be required.

     This function is a GNU extension.  It is meant to work around the
     problems mentioned above.  Now it is possible to convert a buffer
     with multibyte character text piece by piece without having to care
     about inserting NUL bytes and the effect of NUL bytes on the
     conversion state.

   A function to convert a multibyte string into a wide character string
and display it could be written like this (this is not a really useful
example):

     void
     showmbs (const char *src, FILE *fp)
     {
       mbstate_t state;
       int cnt = 0;
       memset (&state, '\0', sizeof (state));
       while (1)
         {
           wchar_t linebuf[100];
           const char *endp = strchr (src, '\n');
           size_t n;

           /* Exit if there is no more line.  */
           if (endp == NULL)
             break;

           n = mbsnrtowcs (linebuf, &src, endp - src, 99, &state);
           linebuf[n] = L'\0';
           fprintf (fp, "line %d: \"%S\"\n", linebuf);
         }
     }

   There is no problem with the state after a call to ‘mbsnrtowcs’.
Since we don’t insert characters in the strings that were not in there
right from the beginning and we use STATE only for the conversion of the
given buffer, there is no problem with altering the state.

 -- Function: size_t wcsnrtombs (char *restrict DST, const wchar_t
          **restrict SRC, size_t NWC, size_t LEN, mbstate_t *restrict
          PS)

     Preliminary: | MT-Unsafe race:wcsnrtombs/!ps | AS-Unsafe corrupt
     heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX
     Safety Concepts::.

     The ‘wcsnrtombs’ function implements the conversion from wide
     character strings to multibyte character strings.  It is similar to
     ‘wcsrtombs’ but, just like ‘mbsnrtowcs’, it takes an extra
     parameter, which specifies the length of the input string.

     No more than NWC wide characters from the input string ‘*SRC’ are
     converted.  If the input string contains a NUL wide character in
     the first NWC characters, the conversion stops at this place.

     The ‘wcsnrtombs’ function is a GNU extension and just like
     ‘mbsnrtowcs’ helps in situations where no NUL-terminated input
     strings are available.


File: libc.info,  Node: Multibyte Conversion Example,  Prev: Converting Strings,  Up: Restartable multibyte conversion

6.3.5 A Complete Multibyte Conversion Example
---------------------------------------------

The example programs given in the last sections are only brief and do
not contain all the error checking, etc.  Presented here is a complete
and documented example.  It features the ‘mbrtowc’ function but it
should be easy to derive versions using the other functions.

     int
     file_mbsrtowcs (int input, int output)
     {
       /* Note the use of ‘MB_LEN_MAX’.
          ‘MB_CUR_MAX’ cannot portably be used here.  */
       char buffer[BUFSIZ + MB_LEN_MAX];
       mbstate_t state;
       int filled = 0;
       int eof = 0;

       /* Initialize the state.  */
       memset (&state, '\0', sizeof (state));

       while (!eof)
         {
           ssize_t nread;
           ssize_t nwrite;
           char *inp = buffer;
           wchar_t outbuf[BUFSIZ];
           wchar_t *outp = outbuf;

           /* Fill up the buffer from the input file.  */
           nread = read (input, buffer + filled, BUFSIZ);
           if (nread < 0)
             {
               perror ("read");
               return 0;
             }
           /* If we reach end of file, make a note to read no more. */
           if (nread == 0)
             eof = 1;

           /* ‘filled’ is now the number of bytes in ‘buffer’. */
           filled += nread;

           /* Convert those bytes to wide characters–as many as we can. */
           while (1)
             {
               size_t thislen = mbrtowc (outp, inp, filled, &state);
               /* Stop converting at invalid character;
                  this can mean we have read just the first part
                  of a valid character.  */
               if (thislen == (size_t) -1)
                 break;
               /* We want to handle embedded NUL bytes
                  but the return value is 0.  Correct this.  */
               if (thislen == 0)
                 thislen = 1;
               /* Advance past this character. */
               inp += thislen;
               filled -= thislen;
               ++outp;
             }

           /* Write the wide characters we just made.  */
           nwrite = write (output, outbuf,
                           (outp - outbuf) * sizeof (wchar_t));
           if (nwrite < 0)
             {
               perror ("write");
               return 0;
             }

           /* See if we have a _real_ invalid character. */
           if ((eof && filled > 0) || filled >= MB_CUR_MAX)
             {
               error (0, 0, "invalid multibyte character");
               return 0;
             }

           /* If any characters must be carried forward,
              put them at the beginning of ‘buffer’. */
           if (filled > 0)
             memmove (buffer, inp, filled);
         }

       return 1;
     }


File: libc.info,  Node: Non-reentrant Conversion,  Next: Generic Charset Conversion,  Prev: Restartable multibyte conversion,  Up: Character Set Handling

6.4 Non-reentrant Conversion Function
=====================================

The functions described in the previous chapter are defined in
Amendment 1 to ISO C90, but the original ISO C90 standard also contained
functions for character set conversion.  The reason that these original
functions are not described first is that they are almost entirely
useless.

   The problem is that all the conversion functions described in the
original ISO C90 use a local state.  Using a local state implies that
multiple conversions at the same time (not only when using threads)
cannot be done, and that you cannot first convert single characters and
then strings since you cannot tell the conversion functions which state
to use.

   These original functions are therefore usable only in a very limited
set of situations.  One must complete converting the entire string
before starting a new one, and each string/text must be converted with
the same function (there is no problem with the library itself; it is
guaranteed that no library function changes the state of any of these
functions).  *For the above reasons it is highly requested that the
functions described in the previous section be used in place of
non-reentrant conversion functions.*

* Menu:

* Non-reentrant Character Conversion::  Non-reentrant Conversion of Single
                                         Characters.
* Non-reentrant String Conversion::     Non-reentrant Conversion of Strings.
* Shift State::                         States in Non-reentrant Functions.


File: libc.info,  Node: Non-reentrant Character Conversion,  Next: Non-reentrant String Conversion,  Up: Non-reentrant Conversion

6.4.1 Non-reentrant Conversion of Single Characters
---------------------------------------------------

 -- Function: int mbtowc (wchar_t *restrict RESULT, const char *restrict
          STRING, size_t SIZE)

     Preliminary: | MT-Unsafe race | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘mbtowc’ (“multibyte to wide character”) function when called
     with non-null STRING converts the first multibyte character
     beginning at STRING to its corresponding wide character code.  It
     stores the result in ‘*RESULT’.

     ‘mbtowc’ never examines more than SIZE bytes.  (The idea is to
     supply for SIZE the number of bytes of data you have in hand.)

     ‘mbtowc’ with non-null STRING distinguishes three possibilities:
     the first SIZE bytes at STRING start with valid multibyte
     characters, they start with an invalid byte sequence or just part
     of a character, or STRING points to an empty string (a null
     character).

     For a valid multibyte character, ‘mbtowc’ converts it to a wide
     character and stores that in ‘*RESULT’, and returns the number of
     bytes in that character (always at least 1 and never more than
     SIZE).

     For an invalid byte sequence, ‘mbtowc’ returns -1.  For an empty
     string, it returns 0, also storing ‘'\0'’ in ‘*RESULT’.

     If the multibyte character code uses shift characters, then
     ‘mbtowc’ maintains and updates a shift state as it scans.  If you
     call ‘mbtowc’ with a null pointer for STRING, that initializes the
     shift state to its standard initial value.  It also returns nonzero
     if the multibyte character code in use actually has a shift state.
     *Note Shift State::.

 -- Function: int wctomb (char *STRING, wchar_t WCHAR)

     Preliminary: | MT-Unsafe race | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘wctomb’ (“wide character to multibyte”) function converts the
     wide character code WCHAR to its corresponding multibyte character
     sequence, and stores the result in bytes starting at STRING.  At
     most ‘MB_CUR_MAX’ characters are stored.

     ‘wctomb’ with non-null STRING distinguishes three possibilities for
     WCHAR: a valid wide character code (one that can be translated to a
     multibyte character), an invalid code, and ‘L'\0'’.

     Given a valid code, ‘wctomb’ converts it to a multibyte character,
     storing the bytes starting at STRING.  Then it returns the number
     of bytes in that character (always at least 1 and never more than
     ‘MB_CUR_MAX’).

     If WCHAR is an invalid wide character code, ‘wctomb’ returns -1.
     If WCHAR is ‘L'\0'’, it returns ‘0’, also storing ‘'\0'’ in
     ‘*STRING’.

     If the multibyte character code uses shift characters, then
     ‘wctomb’ maintains and updates a shift state as it scans.  If you
     call ‘wctomb’ with a null pointer for STRING, that initializes the
     shift state to its standard initial value.  It also returns nonzero
     if the multibyte character code in use actually has a shift state.
     *Note Shift State::.

     Calling this function with a WCHAR argument of zero when STRING is
     not null has the side-effect of reinitializing the stored shift
     state _as well as_ storing the multibyte character ‘'\0'’ and
     returning 0.

   Similar to ‘mbrlen’ there is also a non-reentrant function that
computes the length of a multibyte character.  It can be defined in
terms of ‘mbtowc’.

 -- Function: int mblen (const char *STRING, size_t SIZE)

     Preliminary: | MT-Unsafe race | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘mblen’ function with a non-null STRING argument returns the
     number of bytes that make up the multibyte character beginning at
     STRING, never examining more than SIZE bytes.  (The idea is to
     supply for SIZE the number of bytes of data you have in hand.)

     The return value of ‘mblen’ distinguishes three possibilities: the
     first SIZE bytes at STRING start with valid multibyte characters,
     they start with an invalid byte sequence or just part of a
     character, or STRING points to an empty string (a null character).

     For a valid multibyte character, ‘mblen’ returns the number of
     bytes in that character (always at least ‘1’ and never more than
     SIZE).  For an invalid byte sequence, ‘mblen’ returns -1.  For an
     empty string, it returns 0.

     If the multibyte character code uses shift characters, then ‘mblen’
     maintains and updates a shift state as it scans.  If you call
     ‘mblen’ with a null pointer for STRING, that initializes the shift
     state to its standard initial value.  It also returns a nonzero
     value if the multibyte character code in use actually has a shift
     state.  *Note Shift State::.

     The function ‘mblen’ is declared in ‘stdlib.h’.


File: libc.info,  Node: Non-reentrant String Conversion,  Next: Shift State,  Prev: Non-reentrant Character Conversion,  Up: Non-reentrant Conversion

6.4.2 Non-reentrant Conversion of Strings
-----------------------------------------

For convenience the ISO C90 standard also defines functions to convert
entire strings instead of single characters.  These functions suffer
from the same problems as their reentrant counterparts from Amendment 1
to ISO C90; see *note Converting Strings::.

 -- Function: size_t mbstowcs (wchar_t *WSTRING, const char *STRING,
          size_t SIZE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘mbstowcs’ (“multibyte string to wide character string”)
     function converts the null-terminated string of multibyte
     characters STRING to an array of wide character codes, storing not
     more than SIZE wide characters into the array beginning at WSTRING.
     The terminating null character counts towards the size, so if SIZE
     is less than the actual number of wide characters resulting from
     STRING, no terminating null character is stored.

     The conversion of characters from STRING begins in the initial
     shift state.

     If an invalid multibyte character sequence is found, the ‘mbstowcs’
     function returns a value of -1.  Otherwise, it returns the number
     of wide characters stored in the array WSTRING.  This number does
     not include the terminating null character, which is present if the
     number is less than SIZE.

     Here is an example showing how to convert a string of multibyte
     characters, allocating enough space for the result.

          wchar_t *
          mbstowcs_alloc (const char *string)
          {
            size_t size = strlen (string) + 1;
            wchar_t *buf = xmalloc (size * sizeof (wchar_t));

            size = mbstowcs (buf, string, size);
            if (size == (size_t) -1)
              return NULL;
            buf = xrealloc (buf, (size + 1) * sizeof (wchar_t));
            return buf;
          }

     If WSTRING is a null pointer then no output is written and the
     conversion proceeds as above, and the result is returned.  In
     practice such behaviour is useful for calculating the exact number
     of wide characters required to convert STRING.  This behaviour of
     accepting a null pointer for WSTRING is an XPG4.2 extension that is
     not specified in ISO C and is optional in POSIX.

 -- Function: size_t wcstombs (char *STRING, const wchar_t *WSTRING,
          size_t SIZE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘wcstombs’ (“wide character string to multibyte string”)
     function converts the null-terminated wide character array WSTRING
     into a string containing multibyte characters, storing not more
     than SIZE bytes starting at STRING, followed by a terminating null
     character if there is room.  The conversion of characters begins in
     the initial shift state.

     The terminating null character counts towards the size, so if SIZE
     is less than or equal to the number of bytes needed in WSTRING, no
     terminating null character is stored.

     If a code that does not correspond to a valid multibyte character
     is found, the ‘wcstombs’ function returns a value of -1.
     Otherwise, the return value is the number of bytes stored in the
     array STRING.  This number does not include the terminating null
     character, which is present if the number is less than SIZE.


File: libc.info,  Node: Shift State,  Prev: Non-reentrant String Conversion,  Up: Non-reentrant Conversion

6.4.3 States in Non-reentrant Functions
---------------------------------------

In some multibyte character codes, the _meaning_ of any particular byte
sequence is not fixed; it depends on what other sequences have come
earlier in the same string.  Typically there are just a few sequences
that can change the meaning of other sequences; these few are called
“shift sequences” and we say that they set the “shift state” for other
sequences that follow.

   To illustrate shift state and shift sequences, suppose we decide that
the sequence ‘0200’ (just one byte) enters Japanese mode, in which pairs
of bytes in the range from ‘0240’ to ‘0377’ are single characters, while
‘0201’ enters Latin-1 mode, in which single bytes in the range from
‘0240’ to ‘0377’ are characters, and interpreted according to the ISO
Latin-1 character set.  This is a multibyte code that has two
alternative shift states (“Japanese mode” and “Latin-1 mode”), and two
shift sequences that specify particular shift states.

   When the multibyte character code in use has shift states, then
‘mblen’, ‘mbtowc’, and ‘wctomb’ must maintain and update the current
shift state as they scan the string.  To make this work properly, you
must follow these rules:

   • Before starting to scan a string, call the function with a null
     pointer for the multibyte character address—for example, ‘mblen
     (NULL, 0)’.  This initializes the shift state to its standard
     initial value.

   • Scan the string one character at a time, in order.  Do not “back
     up” and rescan characters already scanned, and do not intersperse
     the processing of different strings.

   Here is an example of using ‘mblen’ following these rules:

     void
     scan_string (char *s)
     {
       int length = strlen (s);

       /* Initialize shift state.  */
       mblen (NULL, 0);

       while (1)
         {
           int thischar = mblen (s, length);
           /* Deal with end of string and invalid characters.  */
           if (thischar == 0)
             break;
           if (thischar == -1)
             {
               error ("invalid multibyte character");
               break;
             }
           /* Advance past this character.  */
           s += thischar;
           length -= thischar;
         }
     }

   The functions ‘mblen’, ‘mbtowc’ and ‘wctomb’ are not reentrant when
using a multibyte code that uses a shift state.  However, no other
library functions call these functions, so you don’t have to worry that
the shift state will be changed mysteriously.


File: libc.info,  Node: Generic Charset Conversion,  Prev: Non-reentrant Conversion,  Up: Character Set Handling

6.5 Generic Charset Conversion
==============================

The conversion functions mentioned so far in this chapter all had in
common that they operate on character sets that are not directly
specified by the functions.  The multibyte encoding used is specified by
the currently selected locale for the ‘LC_CTYPE’ category.  The wide
character set is fixed by the implementation (in the case of the GNU C
Library it is always UCS-4 encoded ISO 10646).

   This has of course several problems when it comes to general
character conversion:

   • For every conversion where neither the source nor the destination
     character set is the character set of the locale for the ‘LC_CTYPE’
     category, one has to change the ‘LC_CTYPE’ locale using
     ‘setlocale’.

     Changing the ‘LC_CTYPE’ locale introduces major problems for the
     rest of the programs since several more functions (e.g., the
     character classification functions, *note Classification of
     Characters::) use the ‘LC_CTYPE’ category.

   • Parallel conversions to and from different character sets are not
     possible since the ‘LC_CTYPE’ selection is global and shared by all
     threads.

   • If neither the source nor the destination character set is the
     character set used for ‘wchar_t’ representation, there is at least
     a two-step process necessary to convert a text using the functions
     above.  One would have to select the source character set as the
     multibyte encoding, convert the text into a ‘wchar_t’ text, select
     the destination character set as the multibyte encoding, and
     convert the wide character text to the multibyte (= destination)
     character set.

     Even if this is possible (which is not guaranteed) it is a very
     tiring work.  Plus it suffers from the other two raised points even
     more due to the steady changing of the locale.

   The XPG2 standard defines a completely new set of functions, which
has none of these limitations.  They are not at all coupled to the
selected locales, and they have no constraints on the character sets
selected for source and destination.  Only the set of available
conversions limits them.  The standard does not specify that any
conversion at all must be available.  Such availability is a measure of
the quality of the implementation.

   In the following text first the interface to ‘iconv’ and then the
conversion function, will be described.  Comparisons with other
implementations will show what obstacles stand in the way of portable
applications.  Finally, the implementation is described in so far as
might interest the advanced user who wants to extend conversion
capabilities.

* Menu:

* Generic Conversion Interface::    Generic Character Set Conversion Interface.
* iconv Examples::                  A complete ‘iconv’ example.
* Other iconv Implementations::     Some Details about other ‘iconv’
                                     Implementations.
* glibc iconv Implementation::      The ‘iconv’ Implementation in the GNU C
                                     library.


File: libc.info,  Node: Generic Conversion Interface,  Next: iconv Examples,  Up: Generic Charset Conversion

6.5.1 Generic Character Set Conversion Interface
------------------------------------------------

This set of functions follows the traditional cycle of using a resource:
open–use–close.  The interface consists of three functions, each of
which implements one step.

   Before the interfaces are described it is necessary to introduce a
data type.  Just like other open–use–close interfaces the functions
introduced here work using handles and the ‘iconv.h’ header defines a
special type for the handles used.

 -- Data Type: iconv_t

     This data type is an abstract type defined in ‘iconv.h’.  The user
     must not assume anything about the definition of this type; it must
     be completely opaque.

     Objects of this type can be assigned handles for the conversions
     using the ‘iconv’ functions.  The objects themselves need not be
     freed, but the conversions for which the handles stand for have to.

The first step is the function to create a handle.

 -- Function: iconv_t iconv_open (const char *TOCODE, const char
          *FROMCODE)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The ‘iconv_open’ function has to be used before starting a
     conversion.  The two parameters this function takes determine the
     source and destination character set for the conversion, and if the
     implementation has the possibility to perform such a conversion,
     the function returns a handle.

     If the wanted conversion is not available, the ‘iconv_open’
     function returns ‘(iconv_t) -1’.  In this case the global variable
     ‘errno’ can have the following values:

     ‘EMFILE’
          The process already has ‘OPEN_MAX’ file descriptors open.
     ‘ENFILE’
          The system limit of open files is reached.
     ‘ENOMEM’
          Not enough memory to carry out the operation.
     ‘EINVAL’
          The conversion from FROMCODE to TOCODE is not supported.

     It is not possible to use the same descriptor in different threads
     to perform independent conversions.  The data structures associated
     with the descriptor include information about the conversion state.
     This must not be messed up by using it in different conversions.

     An ‘iconv’ descriptor is like a file descriptor as for every use a
     new descriptor must be created.  The descriptor does not stand for
     all of the conversions from FROMSET to TOSET.

     The GNU C Library implementation of ‘iconv_open’ has one
     significant extension to other implementations.  To ease the
     extension of the set of available conversions, the implementation
     allows storing the necessary files with data and code in an
     arbitrary number of directories.  How this extension must be
     written will be explained below (*note glibc iconv
     Implementation::).  Here it is only important to say that all
     directories mentioned in the ‘GCONV_PATH’ environment variable are
     considered only if they contain a file ‘gconv-modules’.  These
     directories need not necessarily be created by the system
     administrator.  In fact, this extension is introduced to help users
     writing and using their own, new conversions.  Of course, this does
     not work for security reasons in SUID binaries; in this case only
     the system directory is considered and this normally is
     ‘PREFIX/lib/gconv’.  The ‘GCONV_PATH’ environment variable is
     examined exactly once at the first call of the ‘iconv_open’
     function.  Later modifications of the variable have no effect.

     The ‘iconv_open’ function was introduced early in the X/Open
     Portability Guide, version 2.  It is supported by all commercial
     Unices as it is required for the Unix branding.  However, the
     quality and completeness of the implementation varies widely.  The
     ‘iconv_open’ function is declared in ‘iconv.h’.

   The ‘iconv’ implementation can associate large data structure with
the handle returned by ‘iconv_open’.  Therefore, it is crucial to free
all the resources once all conversions are carried out and the
conversion is not needed anymore.

 -- Function: int iconv_close (iconv_t CD)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock mem | *Note POSIX Safety Concepts::.

     The ‘iconv_close’ function frees all resources associated with the
     handle CD, which must have been returned by a successful call to
     the ‘iconv_open’ function.

     If the function call was successful the return value is 0.
     Otherwise it is -1 and ‘errno’ is set appropriately.  Defined
     errors are:

     ‘EBADF’
          The conversion descriptor is invalid.

     The ‘iconv_close’ function was introduced together with the rest of
     the ‘iconv’ functions in XPG2 and is declared in ‘iconv.h’.

   The standard defines only one actual conversion function.  This has,
therefore, the most general interface: it allows conversion from one
buffer to another.  Conversion from a file to a buffer, vice versa, or
even file to file can be implemented on top of it.

 -- Function: size_t iconv (iconv_t CD, char **INBUF, size_t
          *INBYTESLEFT, char **OUTBUF, size_t *OUTBYTESLEFT)

     Preliminary: | MT-Safe race:cd | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘iconv’ function converts the text in the input buffer
     according to the rules associated with the descriptor CD and stores
     the result in the output buffer.  It is possible to call the
     function for the same text several times in a row since for
     stateful character sets the necessary state information is kept in
     the data structures associated with the descriptor.

     The input buffer is specified by ‘*INBUF’ and it contains
     ‘*INBYTESLEFT’ bytes.  The extra indirection is necessary for
     communicating the used input back to the caller (see below).  It is
     important to note that the buffer pointer is of type ‘char’ and the
     length is measured in bytes even if the input text is encoded in
     wide characters.

     The output buffer is specified in a similar way.  ‘*OUTBUF’ points
     to the beginning of the buffer with at least ‘*OUTBYTESLEFT’ bytes
     room for the result.  The buffer pointer again is of type ‘char’
     and the length is measured in bytes.  If OUTBUF or ‘*OUTBUF’ is a
     null pointer, the conversion is performed but no output is
     available.

     If INBUF is a null pointer, the ‘iconv’ function performs the
     necessary action to put the state of the conversion into the
     initial state.  This is obviously a no-op for non-stateful
     encodings, but if the encoding has a state, such a function call
     might put some byte sequences in the output buffer, which perform
     the necessary state changes.  The next call with INBUF not being a
     null pointer then simply goes on from the initial state.  It is
     important that the programmer never makes any assumption as to
     whether the conversion has to deal with states.  Even if the input
     and output character sets are not stateful, the implementation
     might still have to keep states.  This is due to the implementation
     chosen for the GNU C Library as it is described below.  Therefore
     an ‘iconv’ call to reset the state should always be performed if
     some protocol requires this for the output text.

     The conversion stops for one of three reasons.  The first is that
     all characters from the input buffer are converted.  This actually
     can mean two things: either all bytes from the input buffer are
     consumed or there are some bytes at the end of the buffer that
     possibly can form a complete character but the input is incomplete.
     The second reason for a stop is that the output buffer is full.
     And the third reason is that the input contains invalid characters.

     In all of these cases the buffer pointers after the last successful
     conversion, for the input and output buffers, are stored in INBUF
     and OUTBUF, and the available room in each buffer is stored in
     INBYTESLEFT and OUTBYTESLEFT.

     Since the character sets selected in the ‘iconv_open’ call can be
     almost arbitrary, there can be situations where the input buffer
     contains valid characters, which have no identical representation
     in the output character set.  The behavior in this situation is
     undefined.  The _current_ behavior of the GNU C Library in this
     situation is to return with an error immediately.  This certainly
     is not the most desirable solution; therefore, future versions will
     provide better ones, but they are not yet finished.

     If all input from the input buffer is successfully converted and
     stored in the output buffer, the function returns the number of
     non-reversible conversions performed.  In all other cases the
     return value is ‘(size_t) -1’ and ‘errno’ is set appropriately.  In
     such cases the value pointed to by INBYTESLEFT is nonzero.

     ‘EILSEQ’
          The conversion stopped because of an invalid byte sequence in
          the input.  After the call, ‘*INBUF’ points at the first byte
          of the invalid byte sequence.

     ‘E2BIG’
          The conversion stopped because it ran out of space in the
          output buffer.

     ‘EINVAL’
          The conversion stopped because of an incomplete byte sequence
          at the end of the input buffer.

     ‘EBADF’
          The CD argument is invalid.

     The ‘iconv’ function was introduced in the XPG2 standard and is
     declared in the ‘iconv.h’ header.

   The definition of the ‘iconv’ function is quite good overall.  It
provides quite flexible functionality.  The only problems lie in the
boundary cases, which are incomplete byte sequences at the end of the
input buffer and invalid input.  A third problem, which is not really a
design problem, is the way conversions are selected.  The standard does
not say anything about the legitimate names, a minimal set of available
conversions.  We will see how this negatively impacts other
implementations, as demonstrated below.


File: libc.info,  Node: iconv Examples,  Next: Other iconv Implementations,  Prev: Generic Conversion Interface,  Up: Generic Charset Conversion

6.5.2 A complete ‘iconv’ example
--------------------------------

The example below features a solution for a common problem.  Given that
one knows the internal encoding used by the system for ‘wchar_t’
strings, one often is in the position to read text from a file and store
it in wide character buffers.  One can do this using ‘mbsrtowcs’, but
then we run into the problems discussed above.

     int
     file2wcs (int fd, const char *charset, wchar_t *outbuf, size_t avail)
     {
       char inbuf[BUFSIZ];
       size_t insize = 0;
       char *wrptr = (char *) outbuf;
       int result = 0;
       iconv_t cd;

       cd = iconv_open ("WCHAR_T", charset);
       if (cd == (iconv_t) -1)
         {
           /* Something went wrong.  */
           if (errno == EINVAL)
             error (0, 0, "conversion from '%s' to wchar_t not available",
                    charset);
           else
             perror ("iconv_open");

           /* Terminate the output string.  */
           *outbuf = L'\0';

           return -1;
         }

       while (avail > 0)
         {
           size_t nread;
           size_t nconv;
           char *inptr = inbuf;

           /* Read more input.  */
           nread = read (fd, inbuf + insize, sizeof (inbuf) - insize);
           if (nread == 0)
             {
               /* When we come here the file is completely read.
                  This still could mean there are some unused
                  characters in the ‘inbuf’.  Put them back.  */
               if (lseek (fd, -insize, SEEK_CUR) == -1)
                 result = -1;

               /* Now write out the byte sequence to get into the
                  initial state if this is necessary.  */
               iconv (cd, NULL, NULL, &wrptr, &avail);

               break;
             }
           insize += nread;

           /* Do the conversion.  */
           nconv = iconv (cd, &inptr, &insize, &wrptr, &avail);
           if (nconv == (size_t) -1)
             {
               /* Not everything went right.  It might only be
                  an unfinished byte sequence at the end of the
                  buffer.  Or it is a real problem.  */
               if (errno == EINVAL)
                 /* This is harmless.  Simply move the unused
                    bytes to the beginning of the buffer so that
                    they can be used in the next round.  */
                 memmove (inbuf, inptr, insize);
               else
                 {
                   /* It is a real problem.  Maybe we ran out of
                      space in the output buffer or we have invalid
                      input.  In any case back the file pointer to
                      the position of the last processed byte.  */
                   lseek (fd, -insize, SEEK_CUR);
                   result = -1;
                   break;
                 }
             }
         }

       /* Terminate the output string.  */
       if (avail >= sizeof (wchar_t))
         *((wchar_t *) wrptr) = L'\0';

       if (iconv_close (cd) != 0)
         perror ("iconv_close");

       return (wchar_t *) wrptr - outbuf;
     }

   This example shows the most important aspects of using the ‘iconv’
functions.  It shows how successive calls to ‘iconv’ can be used to
convert large amounts of text.  The user does not have to care about
stateful encodings as the functions take care of everything.

   An interesting point is the case where ‘iconv’ returns an error and
‘errno’ is set to ‘EINVAL’.  This is not really an error in the
transformation.  It can happen whenever the input character set contains
byte sequences of more than one byte for some character and texts are
not processed in one piece.  In this case there is a chance that a
multibyte sequence is cut.  The caller can then simply read the
remainder of the takes and feed the offending bytes together with new
character from the input to ‘iconv’ and continue the work.  The internal
state kept in the descriptor is _not_ unspecified after such an event as
is the case with the conversion functions from the ISO C standard.

   The example also shows the problem of using wide character strings
with ‘iconv’.  As explained in the description of the ‘iconv’ function
above, the function always takes a pointer to a ‘char’ array and the
available space is measured in bytes.  In the example, the output buffer
is a wide character buffer; therefore, we use a local variable WRPTR of
type ‘char *’, which is used in the ‘iconv’ calls.

   This looks rather innocent but can lead to problems on platforms that
have tight restriction on alignment.  Therefore the caller of ‘iconv’
has to make sure that the pointers passed are suitable for access of
characters from the appropriate character set.  Since, in the above
case, the input parameter to the function is a ‘wchar_t’ pointer, this
is the case (unless the user violates alignment when computing the
parameter).  But in other situations, especially when writing generic
functions where one does not know what type of character set one uses
and, therefore, treats text as a sequence of bytes, it might become
tricky.


File: libc.info,  Node: Other iconv Implementations,  Next: glibc iconv Implementation,  Prev: iconv Examples,  Up: Generic Charset Conversion

6.5.3 Some Details about other ‘iconv’ Implementations
------------------------------------------------------

This is not really the place to discuss the ‘iconv’ implementation of
other systems but it is necessary to know a bit about them to write
portable programs.  The above mentioned problems with the specification
of the ‘iconv’ functions can lead to portability issues.

   The first thing to notice is that, due to the large number of
character sets in use, it is certainly not practical to encode the
conversions directly in the C library.  Therefore, the conversion
information must come from files outside the C library.  This is usually
done in one or both of the following ways:

   • The C library contains a set of generic conversion functions that
     can read the needed conversion tables and other information from
     data files.  These files get loaded when necessary.

     This solution is problematic as it requires a great deal of effort
     to apply to all character sets (potentially an infinite set).  The
     differences in the structure of the different character sets is so
     large that many different variants of the table-processing
     functions must be developed.  In addition, the generic nature of
     these functions make them slower than specifically implemented
     functions.

   • The C library only contains a framework that can dynamically load
     object files and execute the conversion functions contained
     therein.

     This solution provides much more flexibility.  The C library itself
     contains only very little code and therefore reduces the general
     memory footprint.  Also, with a documented interface between the C
     library and the loadable modules it is possible for third parties
     to extend the set of available conversion modules.  A drawback of
     this solution is that dynamic loading must be available.

   Some implementations in commercial Unices implement a mixture of
these possibilities; the majority implement only the second solution.
Using loadable modules moves the code out of the library itself and
keeps the door open for extensions and improvements, but this design is
also limiting on some platforms since not many platforms support dynamic
loading in statically linked programs.  On platforms without this
capability it is therefore not possible to use this interface in
statically linked programs.  The GNU C Library has, on ELF platforms, no
problems with dynamic loading in these situations; therefore, this point
is moot.  The danger is that one gets acquainted with this situation and
forgets about the restrictions on other systems.

   A second thing to know about other ‘iconv’ implementations is that
the number of available conversions is often very limited.  Some
implementations provide, in the standard release (not special
international or developer releases), at most 100 to 200 conversion
possibilities.  This does not mean 200 different character sets are
supported; for example, conversions from one character set to a set of
10 others might count as 10 conversions.  Together with the other
direction this makes 20 conversion possibilities used up by one
character set.  One can imagine the thin coverage these platforms
provide.  Some Unix vendors even provide only a handful of conversions,
which renders them useless for almost all uses.

   This directly leads to a third and probably the most problematic
point.  The way the ‘iconv’ conversion functions are implemented on all
known Unix systems and the availability of the conversion functions from
character set A to B and the conversion from B to C does _not_ imply
that the conversion from A to C is available.

   This might not seem unreasonable and problematic at first, but it is
a quite big problem as one will notice shortly after hitting it.  To
show the problem we assume to write a program that has to convert from A
to C. A call like

     cd = iconv_open ("C", "A");

fails according to the assumption above.  But what does the program do
now?  The conversion is necessary; therefore, simply giving up is not an
option.

   This is a nuisance.  The ‘iconv’ function should take care of this.
But how should the program proceed from here on?  If it tries to convert
to character set B, first the two ‘iconv_open’ calls

     cd1 = iconv_open ("B", "A");

and

     cd2 = iconv_open ("C", "B");

will succeed, but how to find B?

   Unfortunately, the answer is: there is no general solution.  On some
systems guessing might help.  On those systems most character sets can
convert to and from UTF-8 encoded ISO 10646 or Unicode text.  Besides
this only some very system-specific methods can help.  Since the
conversion functions come from loadable modules and these modules must
be stored somewhere in the filesystem, one _could_ try to find them and
determine from the available file which conversions are available and
whether there is an indirect route from A to C.

   This example shows one of the design errors of ‘iconv’ mentioned
above.  It should at least be possible to determine the list of
available conversions programmatically so that if ‘iconv_open’ says
there is no such conversion, one could make sure this also is true for
indirect routes.


File: libc.info,  Node: glibc iconv Implementation,  Prev: Other iconv Implementations,  Up: Generic Charset Conversion

6.5.4 The ‘iconv’ Implementation in the GNU C Library
-----------------------------------------------------

After reading about the problems of ‘iconv’ implementations in the last
section it is certainly good to note that the implementation in the GNU
C Library has none of the problems mentioned above.  What follows is a
step-by-step analysis of the points raised above.  The evaluation is
based on the current state of the development (as of January 1999).  The
development of the ‘iconv’ functions is not complete, but basic
functionality has solidified.

   The GNU C Library’s ‘iconv’ implementation uses shared loadable
modules to implement the conversions.  A very small number of
conversions are built into the library itself but these are only rather
trivial conversions.

   All the benefits of loadable modules are available in the GNU C
Library implementation.  This is especially appealing since the
interface is well documented (see below), and it, therefore, is easy to
write new conversion modules.  The drawback of using loadable objects is
not a problem in the GNU C Library, at least on ELF systems.  Since the
library is able to load shared objects even in statically linked
binaries, static linking need not be forbidden in case one wants to use
‘iconv’.

   The second mentioned problem is the number of supported conversions.
Currently, the GNU C Library supports more than 150 character sets.  The
way the implementation is designed the number of supported conversions
is greater than 22350 (150 times 149).  If any conversion from or to a
character set is missing, it can be added easily.

   Particularly impressive as it may be, this high number is due to the
fact that the GNU C Library implementation of ‘iconv’ does not have the
third problem mentioned above (i.e., whenever there is a conversion from
a character set A to B and from B to C it is always possible to convert
from A to C directly).  If the ‘iconv_open’ returns an error and sets
‘errno’ to ‘EINVAL’, there is no known way, directly or indirectly, to
perform the wanted conversion.

   Triangulation is achieved by providing for each character set a
conversion from and to UCS-4 encoded ISO 10646.  Using ISO 10646 as an
intermediate representation it is possible to “triangulate” (i.e.,
convert with an intermediate representation).

   There is no inherent requirement to provide a conversion to ISO 10646
for a new character set, and it is also possible to provide other
conversions where neither source nor destination character set is
ISO 10646.  The existing set of conversions is simply meant to cover all
conversions that might be of interest.

   All currently available conversions use the triangulation method
above, making conversion run unnecessarily slow.  If, for example,
somebody often needs the conversion from ISO-2022-JP to EUC-JP, a
quicker solution would involve direct conversion between the two
character sets, skipping the input to ISO 10646 first.  The two
character sets of interest are much more similar to each other than to
ISO 10646.

   In such a situation one easily can write a new conversion and provide
it as a better alternative.  The GNU C Library ‘iconv’ implementation
would automatically use the module implementing the conversion if it is
specified to be more efficient.

6.5.4.1 Format of ‘gconv-modules’ files
.......................................

All information about the available conversions comes from a file named
‘gconv-modules’, which can be found in any of the directories along the
‘GCONV_PATH’.  The ‘gconv-modules’ files are line-oriented text files,
where each of the lines has one of the following formats:

   • If the first non-whitespace character is a ‘#’ the line contains
     only comments and is ignored.

   • Lines starting with ‘alias’ define an alias name for a character
     set.  Two more words are expected on the line.  The first word
     defines the alias name, and the second defines the original name of
     the character set.  The effect is that it is possible to use the
     alias name in the FROMSET or TOSET parameters of ‘iconv_open’ and
     achieve the same result as when using the real character set name.

     This is quite important as a character set has often many different
     names.  There is normally an official name but this need not
     correspond to the most popular name.  Besides this many character
     sets have special names that are somehow constructed.  For example,
     all character sets specified by the ISO have an alias of the form
     ‘ISO-IR-NNN’ where NNN is the registration number.  This allows
     programs that know about the registration number to construct
     character set names and use them in ‘iconv_open’ calls.  More on
     the available names and aliases follows below.

   • Lines starting with ‘module’ introduce an available conversion
     module.  These lines must contain three or four more words.

     The first word specifies the source character set, the second word
     the destination character set of conversion implemented in this
     module, and the third word is the name of the loadable module.  The
     filename is constructed by appending the usual shared object suffix
     (normally ‘.so’) and this file is then supposed to be found in the
     same directory the ‘gconv-modules’ file is in.  The last word on
     the line, which is optional, is a numeric value representing the
     cost of the conversion.  If this word is missing, a cost of 1 is
     assumed.  The numeric value itself does not matter that much; what
     counts are the relative values of the sums of costs for all
     possible conversion paths.  Below is a more precise description of
     the use of the cost value.

   Returning to the example above where one has written a module to
directly convert from ISO-2022-JP to EUC-JP and back.  All that has to
be done is to put the new module, let its name be ISO2022JP-EUCJP.so, in
a directory and add a file ‘gconv-modules’ with the following content in
the same directory:

     module  ISO-2022-JP//   EUC-JP//        ISO2022JP-EUCJP    1
     module  EUC-JP//        ISO-2022-JP//   ISO2022JP-EUCJP    1

   To see why this is sufficient, it is necessary to understand how the
conversion used by ‘iconv’ (and described in the descriptor) is
selected.  The approach to this problem is quite simple.

   At the first call of the ‘iconv_open’ function the program reads all
available ‘gconv-modules’ files and builds up two tables: one containing
all the known aliases and another that contains the information about
the conversions and which shared object implements them.

6.5.4.2 Finding the conversion path in ‘iconv’
..............................................

The set of available conversions form a directed graph with weighted
edges.  The weights on the edges are the costs specified in the
‘gconv-modules’ files.  The ‘iconv_open’ function uses an algorithm
suitable for search for the best path in such a graph and so constructs
a list of conversions that must be performed in succession to get the
transformation from the source to the destination character set.

   Explaining why the above ‘gconv-modules’ files allows the ‘iconv’
implementation to resolve the specific ISO-2022-JP to EUC-JP conversion
module instead of the conversion coming with the library itself is
straightforward.  Since the latter conversion takes two steps (from
ISO-2022-JP to ISO 10646 and then from ISO 10646 to EUC-JP), the cost is
1+1 = 2.  The above ‘gconv-modules’ file, however, specifies that the
new conversion modules can perform this conversion with only the cost of
1.

   A mysterious item about the ‘gconv-modules’ file above (and also the
file coming with the GNU C Library) are the names of the character sets
specified in the ‘module’ lines.  Why do almost all the names end in
‘//’?  And this is not all: the names can actually be regular
expressions.  At this point in time this mystery should not be revealed,
unless you have the relevant spell-casting materials: ashes from an
original DOS 6.2 boot disk burnt in effigy, a crucifix blessed by St.
Emacs, assorted herbal roots from Central America, sand from Cebu, etc.
Sorry!  *The part of the implementation where this is used is not yet
finished.  For now please simply follow the existing examples.  It’ll
become clearer once it is.  –drepper*

   A last remark about the ‘gconv-modules’ is about the names not ending
with ‘//’.  A character set named ‘INTERNAL’ is often mentioned.  From
the discussion above and the chosen name it should have become clear
that this is the name for the representation used in the intermediate
step of the triangulation.  We have said that this is UCS-4 but actually
that is not quite right.  The UCS-4 specification also includes the
specification of the byte ordering used.  Since a UCS-4 value consists
of four bytes, a stored value is affected by byte ordering.  The
internal representation is _not_ the same as UCS-4 in case the byte
ordering of the processor (or at least the running process) is not the
same as the one required for UCS-4.  This is done for performance
reasons as one does not want to perform unnecessary byte-swapping
operations if one is not interested in actually seeing the result in
UCS-4.  To avoid trouble with endianness, the internal representation
consistently is named ‘INTERNAL’ even on big-endian systems where the
representations are identical.

6.5.4.3 ‘iconv’ module data structures
......................................

So far this section has described how modules are located and considered
to be used.  What remains to be described is the interface of the
modules so that one can write new ones.  This section describes the
interface as it is in use in January 1999.  The interface will change a
bit in the future but, with luck, only in an upwardly compatible way.

   The definitions necessary to write new modules are publicly available
in the non-standard header ‘gconv.h’.  The following text, therefore,
describes the definitions from this header file.  First, however, it is
necessary to get an overview.

   From the perspective of the user of ‘iconv’ the interface is quite
simple: the ‘iconv_open’ function returns a handle that can be used in
calls to ‘iconv’, and finally the handle is freed with a call to
‘iconv_close’.  The problem is that the handle has to be able to
represent the possibly long sequences of conversion steps and also the
state of each conversion since the handle is all that is passed to the
‘iconv’ function.  Therefore, the data structures are really the
elements necessary to understanding the implementation.

   We need two different kinds of data structures.  The first describes
the conversion and the second describes the state etc.  There are really
two type definitions like this in ‘gconv.h’.

 -- Data type: struct __gconv_step

     This data structure describes one conversion a module can perform.
     For each function in a loaded module with conversion functions
     there is exactly one object of this type.  This object is shared by
     all users of the conversion (i.e., this object does not contain any
     information corresponding to an actual conversion; it only
     describes the conversion itself).

     ‘struct __gconv_loaded_object *__shlib_handle’
     ‘const char *__modname’
     ‘int __counter’
          All these elements of the structure are used internally in the
          C library to coordinate loading and unloading the shared
          object.  One must not expect any of the other elements to be
          available or initialized.

     ‘const char *__from_name’
     ‘const char *__to_name’
          ‘__from_name’ and ‘__to_name’ contain the names of the source
          and destination character sets.  They can be used to identify
          the actual conversion to be carried out since one module might
          implement conversions for more than one character set and/or
          direction.

     ‘gconv_fct __fct’
     ‘gconv_init_fct __init_fct’
     ‘gconv_end_fct __end_fct’
          These elements contain pointers to the functions in the
          loadable module.  The interface will be explained below.

     ‘int __min_needed_from’
     ‘int __max_needed_from’
     ‘int __min_needed_to’
     ‘int __max_needed_to;’
          These values have to be supplied in the init function of the
          module.  The ‘__min_needed_from’ value specifies how many
          bytes a character of the source character set at least needs.
          The ‘__max_needed_from’ specifies the maximum value that also
          includes possible shift sequences.

          The ‘__min_needed_to’ and ‘__max_needed_to’ values serve the
          same purpose as ‘__min_needed_from’ and ‘__max_needed_from’
          but this time for the destination character set.

          It is crucial that these values be accurate since otherwise
          the conversion functions will have problems or not work at
          all.

     ‘int __stateful’
          This element must also be initialized by the init function.
          ‘int __stateful’ is nonzero if the source character set is
          stateful.  Otherwise it is zero.

     ‘void *__data’
          This element can be used freely by the conversion functions in
          the module.  ‘void *__data’ can be used to communicate extra
          information from one call to another.  ‘void *__data’ need not
          be initialized if not needed at all.  If ‘void *__data’
          element is assigned a pointer to dynamically allocated memory
          (presumably in the init function) it has to be made sure that
          the end function deallocates the memory.  Otherwise the
          application will leak memory.

          It is important to be aware that this data structure is shared
          by all users of this specification conversion and therefore
          the ‘__data’ element must not contain data specific to one
          specific use of the conversion function.

 -- Data type: struct __gconv_step_data

     This is the data structure that contains the information specific
     to each use of the conversion functions.

     ‘char *__outbuf’
     ‘char *__outbufend’
          These elements specify the output buffer for the conversion
          step.  The ‘__outbuf’ element points to the beginning of the
          buffer, and ‘__outbufend’ points to the byte following the
          last byte in the buffer.  The conversion function must not
          assume anything about the size of the buffer but it can be
          safely assumed there is room for at least one complete
          character in the output buffer.

          Once the conversion is finished, if the conversion is the last
          step, the ‘__outbuf’ element must be modified to point after
          the last byte written into the buffer to signal how much
          output is available.  If this conversion step is not the last
          one, the element must not be modified.  The ‘__outbufend’
          element must not be modified.

     ‘int __is_last’
          This element is nonzero if this conversion step is the last
          one.  This information is necessary for the recursion.  See
          the description of the conversion function internals below.
          This element must never be modified.

     ‘int __invocation_counter’
          The conversion function can use this element to see how many
          calls of the conversion function already happened.  Some
          character sets require a certain prolog when generating
          output, and by comparing this value with zero, one can find
          out whether it is the first call and whether, therefore, the
          prolog should be emitted.  This element must never be
          modified.

     ‘int __internal_use’
          This element is another one rarely used but needed in certain
          situations.  It is assigned a nonzero value in case the
          conversion functions are used to implement ‘mbsrtowcs’ et.al.
          (i.e., the function is not used directly through the ‘iconv’
          interface).

          This sometimes makes a difference as it is expected that the
          ‘iconv’ functions are used to translate entire texts while the
          ‘mbsrtowcs’ functions are normally used only to convert single
          strings and might be used multiple times to convert entire
          texts.

          But in this situation we would have problem complying with
          some rules of the character set specification.  Some character
          sets require a prolog, which must appear exactly once for an
          entire text.  If a number of ‘mbsrtowcs’ calls are used to
          convert the text, only the first call must add the prolog.
          However, because there is no communication between the
          different calls of ‘mbsrtowcs’, the conversion functions have
          no possibility to find this out.  The situation is different
          for sequences of ‘iconv’ calls since the handle allows access
          to the needed information.

          The ‘int __internal_use’ element is mostly used together with
          ‘__invocation_counter’ as follows:

               if (!data->__internal_use
                    && data->__invocation_counter == 0)
                 /* Emit prolog.  */
                 ...

          This element must never be modified.

     ‘mbstate_t *__statep’
          The ‘__statep’ element points to an object of type ‘mbstate_t’
          (*note Keeping the state::).  The conversion of a stateful
          character set must use the object pointed to by ‘__statep’ to
          store information about the conversion state.  The ‘__statep’
          element itself must never be modified.

     ‘mbstate_t __state’
          This element must _never_ be used directly.  It is only part
          of this structure to have the needed space allocated.

6.5.4.4 ‘iconv’ module interfaces
.................................

With the knowledge about the data structures we now can describe the
conversion function itself.  To understand the interface a bit of
knowledge is necessary about the functionality in the C library that
loads the objects with the conversions.

   It is often the case that one conversion is used more than once
(i.e., there are several ‘iconv_open’ calls for the same set of
character sets during one program run).  The ‘mbsrtowcs’ et.al.
functions in the GNU C Library also use the ‘iconv’ functionality, which
increases the number of uses of the same functions even more.

   Because of this multiple use of conversions, the modules do not get
loaded exclusively for one conversion.  Instead a module once loaded can
be used by an arbitrary number of ‘iconv’ or ‘mbsrtowcs’ calls at the
same time.  The splitting of the information between conversion-
function-specific information and conversion data makes this possible.
The last section showed the two data structures used to do this.

   This is of course also reflected in the interface and semantics of
the functions that the modules must provide.  There are three functions
that must have the following names:

‘gconv_init’
     The ‘gconv_init’ function initializes the conversion function
     specific data structure.  This very same object is shared by all
     conversions that use this conversion and, therefore, no state
     information about the conversion itself must be stored in here.  If
     a module implements more than one conversion, the ‘gconv_init’
     function will be called multiple times.

‘gconv_end’
     The ‘gconv_end’ function is responsible for freeing all resources
     allocated by the ‘gconv_init’ function.  If there is nothing to do,
     this function can be missing.  Special care must be taken if the
     module implements more than one conversion and the ‘gconv_init’
     function does not allocate the same resources for all conversions.

‘gconv’
     This is the actual conversion function.  It is called to convert
     one block of text.  It gets passed the conversion step information
     initialized by ‘gconv_init’ and the conversion data, specific to
     this use of the conversion functions.

   There are three data types defined for the three module interface
functions and these define the interface.

 -- Data type: int (*__gconv_init_fct) (struct __gconv_step *)

     This specifies the interface of the initialization function of the
     module.  It is called exactly once for each conversion the module
     implements.

     As explained in the description of the ‘struct __gconv_step’ data
     structure above the initialization function has to initialize parts
     of it.

     ‘__min_needed_from’
     ‘__max_needed_from’
     ‘__min_needed_to’
     ‘__max_needed_to’
          These elements must be initialized to the exact numbers of the
          minimum and maximum number of bytes used by one character in
          the source and destination character sets, respectively.  If
          the characters all have the same size, the minimum and maximum
          values are the same.

     ‘__stateful’
          This element must be initialized to a nonzero value if the
          source character set is stateful.  Otherwise it must be zero.

     If the initialization function needs to communicate some
     information to the conversion function, this communication can
     happen using the ‘__data’ element of the ‘__gconv_step’ structure.
     But since this data is shared by all the conversions, it must not
     be modified by the conversion function.  The example below shows
     how this can be used.

          #define MIN_NEEDED_FROM         1
          #define MAX_NEEDED_FROM         4
          #define MIN_NEEDED_TO           4
          #define MAX_NEEDED_TO           4

          int
          gconv_init (struct __gconv_step *step)
          {
            /* Determine which direction.  */
            struct iso2022jp_data *new_data;
            enum direction dir = illegal_dir;
            enum variant var = illegal_var;
            int result;

            if (__strcasecmp (step->__from_name, "ISO-2022-JP//") == 0)
              {
                dir = from_iso2022jp;
                var = iso2022jp;
              }
            else if (__strcasecmp (step->__to_name, "ISO-2022-JP//") == 0)
              {
                dir = to_iso2022jp;
                var = iso2022jp;
              }
            else if (__strcasecmp (step->__from_name, "ISO-2022-JP-2//") == 0)
              {
                dir = from_iso2022jp;
                var = iso2022jp2;
              }
            else if (__strcasecmp (step->__to_name, "ISO-2022-JP-2//") == 0)
              {
                dir = to_iso2022jp;
                var = iso2022jp2;
              }

            result = __GCONV_NOCONV;
            if (dir != illegal_dir)
              {
                new_data = (struct iso2022jp_data *)
                  malloc (sizeof (struct iso2022jp_data));

                result = __GCONV_NOMEM;
                if (new_data != NULL)
                  {
                    new_data->dir = dir;
                    new_data->var = var;
                    step->__data = new_data;

                    if (dir == from_iso2022jp)
                      {
                        step->__min_needed_from = MIN_NEEDED_FROM;
                        step->__max_needed_from = MAX_NEEDED_FROM;
                        step->__min_needed_to = MIN_NEEDED_TO;
                        step->__max_needed_to = MAX_NEEDED_TO;
                      }
                    else
                      {
                        step->__min_needed_from = MIN_NEEDED_TO;
                        step->__max_needed_from = MAX_NEEDED_TO;
                        step->__min_needed_to = MIN_NEEDED_FROM;
                        step->__max_needed_to = MAX_NEEDED_FROM + 2;
                      }

                    /* Yes, this is a stateful encoding.  */
                    step->__stateful = 1;

                    result = __GCONV_OK;
                  }
              }

            return result;
          }

     The function first checks which conversion is wanted.  The module
     from which this function is taken implements four different
     conversions; which one is selected can be determined by comparing
     the names.  The comparison should always be done without paying
     attention to the case.

     Next, a data structure, which contains the necessary information
     about which conversion is selected, is allocated.  The data
     structure ‘struct iso2022jp_data’ is locally defined since, outside
     the module, this data is not used at all.  Please note that if all
     four conversions this module supports are requested there are four
     data blocks.

     One interesting thing is the initialization of the ‘__min_’ and
     ‘__max_’ elements of the step data object.  A single ISO-2022-JP
     character can consist of one to four bytes.  Therefore the
     ‘MIN_NEEDED_FROM’ and ‘MAX_NEEDED_FROM’ macros are defined this
     way.  The output is always the ‘INTERNAL’ character set (aka UCS-4)
     and therefore each character consists of exactly four bytes.  For
     the conversion from ‘INTERNAL’ to ISO-2022-JP we have to take into
     account that escape sequences might be necessary to switch the
     character sets.  Therefore the ‘__max_needed_to’ element for this
     direction gets assigned ‘MAX_NEEDED_FROM + 2’.  This takes into
     account the two bytes needed for the escape sequences to signal the
     switching.  The asymmetry in the maximum values for the two
     directions can be explained easily: when reading ISO-2022-JP text,
     escape sequences can be handled alone (i.e., it is not necessary to
     process a real character since the effect of the escape sequence
     can be recorded in the state information).  The situation is
     different for the other direction.  Since it is in general not
     known which character comes next, one cannot emit escape sequences
     to change the state in advance.  This means the escape sequences
     have to be emitted together with the next character.  Therefore one
     needs more room than only for the character itself.

     The possible return values of the initialization function are:

     ‘__GCONV_OK’
          The initialization succeeded
     ‘__GCONV_NOCONV’
          The requested conversion is not supported in the module.  This
          can happen if the ‘gconv-modules’ file has errors.
     ‘__GCONV_NOMEM’
          Memory required to store additional information could not be
          allocated.

   The function called before the module is unloaded is significantly
easier.  It often has nothing at all to do; in which case it can be left
out completely.

 -- Data type: void (*__gconv_end_fct) (struct gconv_step *)

     The task of this function is to free all resources allocated in the
     initialization function.  Therefore only the ‘__data’ element of
     the object pointed to by the argument is of interest.  Continuing
     the example from the initialization function, the finalization
     function looks like this:

          void
          gconv_end (struct __gconv_step *data)
          {
            free (data->__data);
          }

   The most important function is the conversion function itself, which
can get quite complicated for complex character sets.  But since this is
not of interest here, we will only describe a possible skeleton for the
conversion function.

 -- Data type: int (*__gconv_fct) (struct __gconv_step *, struct
          __gconv_step_data *, const char **, const char *, size_t *,
          int)

     The conversion function can be called for two basic reasons: to
     convert text or to reset the state.  From the description of the
     ‘iconv’ function it can be seen why the flushing mode is necessary.
     What mode is selected is determined by the sixth argument, an
     integer.  This argument being nonzero means that flushing is
     selected.

     Common to both modes is where the output buffer can be found.  The
     information about this buffer is stored in the conversion step
     data.  A pointer to this information is passed as the second
     argument to this function.  The description of the ‘struct
     __gconv_step_data’ structure has more information on the conversion
     step data.

     What has to be done for flushing depends on the source character
     set.  If the source character set is not stateful, nothing has to
     be done.  Otherwise the function has to emit a byte sequence to
     bring the state object into the initial state.  Once this all
     happened the other conversion modules in the chain of conversions
     have to get the same chance.  Whether another step follows can be
     determined from the ‘__is_last’ element of the step data structure
     to which the first parameter points.

     The more interesting mode is when actual text has to be converted.
     The first step in this case is to convert as much text as possible
     from the input buffer and store the result in the output buffer.
     The start of the input buffer is determined by the third argument,
     which is a pointer to a pointer variable referencing the beginning
     of the buffer.  The fourth argument is a pointer to the byte right
     after the last byte in the buffer.

     The conversion has to be performed according to the current state
     if the character set is stateful.  The state is stored in an object
     pointed to by the ‘__statep’ element of the step data (second
     argument).  Once either the input buffer is empty or the output
     buffer is full the conversion stops.  At this point, the pointer
     variable referenced by the third parameter must point to the byte
     following the last processed byte (i.e., if all of the input is
     consumed, this pointer and the fourth parameter have the same
     value).

     What now happens depends on whether this step is the last one.  If
     it is the last step, the only thing that has to be done is to
     update the ‘__outbuf’ element of the step data structure to point
     after the last written byte.  This update gives the caller the
     information on how much text is available in the output buffer.  In
     addition, the variable pointed to by the fifth parameter, which is
     of type ‘size_t’, must be incremented by the number of characters
     (_not bytes_) that were converted in a non-reversible way.  Then,
     the function can return.

     In case the step is not the last one, the later conversion
     functions have to get a chance to do their work.  Therefore, the
     appropriate conversion function has to be called.  The information
     about the functions is stored in the conversion data structures,
     passed as the first parameter.  This information and the step data
     are stored in arrays, so the next element in both cases can be
     found by simple pointer arithmetic:

          int
          gconv (struct __gconv_step *step, struct __gconv_step_data *data,
                 const char **inbuf, const char *inbufend, size_t *written,
                 int do_flush)
          {
            struct __gconv_step *next_step = step + 1;
            struct __gconv_step_data *next_data = data + 1;
            ...

     The ‘next_step’ pointer references the next step information and
     ‘next_data’ the next data record.  The call of the next function
     therefore will look similar to this:

            next_step->__fct (next_step, next_data, &outerr, outbuf,
                              written, 0)

     But this is not yet all.  Once the function call returns the
     conversion function might have some more to do.  If the return
     value of the function is ‘__GCONV_EMPTY_INPUT’, more room is
     available in the output buffer.  Unless the input buffer is empty,
     the conversion functions start all over again and process the rest
     of the input buffer.  If the return value is not
     ‘__GCONV_EMPTY_INPUT’, something went wrong and we have to recover
     from this.

     A requirement for the conversion function is that the input buffer
     pointer (the third argument) always point to the last character
     that was put in converted form into the output buffer.  This is
     trivially true after the conversion performed in the current step,
     but if the conversion functions deeper downstream stop prematurely,
     not all characters from the output buffer are consumed and,
     therefore, the input buffer pointers must be backed off to the
     right position.

     Correcting the input buffers is easy to do if the input and output
     character sets have a fixed width for all characters.  In this
     situation we can compute how many characters are left in the output
     buffer and, therefore, can correct the input buffer pointer
     appropriately with a similar computation.  Things are getting
     tricky if either character set has characters represented with
     variable length byte sequences, and it gets even more complicated
     if the conversion has to take care of the state.  In these cases
     the conversion has to be performed once again, from the known state
     before the initial conversion (i.e., if necessary the state of the
     conversion has to be reset and the conversion loop has to be
     executed again).  The difference now is that it is known how much
     input must be created, and the conversion can stop before
     converting the first unused character.  Once this is done the input
     buffer pointers must be updated again and the function can return.

     One final thing should be mentioned.  If it is necessary for the
     conversion to know whether it is the first invocation (in case a
     prolog has to be emitted), the conversion function should increment
     the ‘__invocation_counter’ element of the step data structure just
     before returning to the caller.  See the description of the ‘struct
     __gconv_step_data’ structure above for more information on how this
     can be used.

     The return value must be one of the following values:

     ‘__GCONV_EMPTY_INPUT’
          All input was consumed and there is room left in the output
          buffer.
     ‘__GCONV_FULL_OUTPUT’
          No more room in the output buffer.  In case this is not the
          last step this value is propagated down from the call of the
          next conversion function in the chain.
     ‘__GCONV_INCOMPLETE_INPUT’
          The input buffer is not entirely empty since it contains an
          incomplete character sequence.

     The following example provides a framework for a conversion
     function.  In case a new conversion has to be written the holes in
     this implementation have to be filled and that is it.

          int
          gconv (struct __gconv_step *step, struct __gconv_step_data *data,
                 const char **inbuf, const char *inbufend, size_t *written,
                 int do_flush)
          {
            struct __gconv_step *next_step = step + 1;
            struct __gconv_step_data *next_data = data + 1;
            gconv_fct fct = next_step->__fct;
            int status;

            /* If the function is called with no input this means we have
               to reset to the initial state.  The possibly partly
               converted input is dropped.  */
            if (do_flush)
              {
                status = __GCONV_OK;

                /* Possible emit a byte sequence which put the state object
                   into the initial state.  */

                /* Call the steps down the chain if there are any but only
                   if we successfully emitted the escape sequence.  */
                if (status == __GCONV_OK && ! data->__is_last)
                  status = fct (next_step, next_data, NULL, NULL,
                                written, 1);
              }
            else
              {
                /* We preserve the initial values of the pointer variables.  */
                const char *inptr = *inbuf;
                char *outbuf = data->__outbuf;
                char *outend = data->__outbufend;
                char *outptr;

                do
                  {
                    /* Remember the start value for this round.  */
                    inptr = *inbuf;
                    /* The outbuf buffer is empty.  */
                    outptr = outbuf;

                    /* For stateful encodings the state must be safe here.  */

                    /* Run the conversion loop.  ‘status’ is set
                       appropriately afterwards.  */

                    /* If this is the last step, leave the loop.  There is
                       nothing we can do.  */
                    if (data->__is_last)
                      {
                        /* Store information about how many bytes are
                           available.  */
                        data->__outbuf = outbuf;

                       /* If any non-reversible conversions were performed,
                          add the number to ‘*written’.  */

                       break;
                     }

                    /* Write out all output that was produced.  */
                    if (outbuf > outptr)
                      {
                        const char *outerr = data->__outbuf;
                        int result;

                        result = fct (next_step, next_data, &outerr,
                                      outbuf, written, 0);

                        if (result != __GCONV_EMPTY_INPUT)
                          {
                            if (outerr != outbuf)
                              {
                                /* Reset the input buffer pointer.  We
                                   document here the complex case.  */
                                size_t nstatus;

                                /* Reload the pointers.  */
                                *inbuf = inptr;
                                outbuf = outptr;

                                /* Possibly reset the state.  */

                                /* Redo the conversion, but this time
                                   the end of the output buffer is at
                                   ‘outerr’.  */
                              }

                            /* Change the status.  */
                            status = result;
                          }
                        else
                          /* All the output is consumed, we can make
                              another run if everything was ok.  */
                          if (status == __GCONV_FULL_OUTPUT)
                            status = __GCONV_OK;
                     }
                  }
                while (status == __GCONV_OK);

                /* We finished one use of this step.  */
                ++data->__invocation_counter;
              }

            return status;
          }

   This information should be sufficient to write new modules.  Anybody
doing so should also take a look at the available source code in the GNU
C Library sources.  It contains many examples of working and optimized
modules.


File: libc.info,  Node: Locales,  Next: Message Translation,  Prev: Character Set Handling,  Up: Top

7 Locales and Internationalization
**********************************

Different countries and cultures have varying conventions for how to
communicate.  These conventions range from very simple ones, such as the
format for representing dates and times, to very complex ones, such as
the language spoken.

   “Internationalization” of software means programming it to be able to
adapt to the user’s favorite conventions.  In ISO C,
internationalization works by means of “locales”.  Each locale specifies
a collection of conventions, one convention for each purpose.  The user
chooses a set of conventions by specifying a locale (via environment
variables).

   All programs inherit the chosen locale as part of their environment.
Provided the programs are written to obey the choice of locale, they
will follow the conventions preferred by the user.

* Menu:

* Effects of Locale::           Actions affected by the choice of
                                 locale.
* Choosing Locale::             How the user specifies a locale.
* Locale Categories::           Different purposes for which you can
                                 select a locale.
* Setting the Locale::          How a program specifies the locale
                                 with library functions.
* Standard Locales::            Locale names available on all systems.
* Locale Names::                Format of system-specific locale names.
* Locale Information::          How to access the information for the locale.
* Formatting Numbers::          A dedicated function to format numbers.
* Yes-or-No Questions::         Check a Response against the locale.


File: libc.info,  Node: Effects of Locale,  Next: Choosing Locale,  Up: Locales

7.1 What Effects a Locale Has
=============================

Each locale specifies conventions for several purposes, including the
following:

   • What multibyte character sequences are valid, and how they are
     interpreted (*note Character Set Handling::).

   • Classification of which characters in the local character set are
     considered alphabetic, and upper- and lower-case conversion
     conventions (*note Character Handling::).

   • The collating sequence for the local language and character set
     (*note Collation Functions::).

   • Formatting of numbers and currency amounts (*note General
     Numeric::).

   • Formatting of dates and times (*note Formatting Calendar Time::).

   • What language to use for output, including error messages (*note
     Message Translation::).

   • What language to use for user answers to yes-or-no questions (*note
     Yes-or-No Questions::).

   • What language to use for more complex user input.  (The C library
     doesn’t yet help you implement this.)

   Some aspects of adapting to the specified locale are handled
automatically by the library subroutines.  For example, all your program
needs to do in order to use the collating sequence of the chosen locale
is to use ‘strcoll’ or ‘strxfrm’ to compare strings.

   Other aspects of locales are beyond the comprehension of the library.
For example, the library can’t automatically translate your program’s
output messages into other languages.  The only way you can support
output in the user’s favorite language is to program this more or less
by hand.  The C library provides functions to handle translations for
multiple languages easily.

   This chapter discusses the mechanism by which you can modify the
current locale.  The effects of the current locale on specific library
functions are discussed in more detail in the descriptions of those
functions.


File: libc.info,  Node: Choosing Locale,  Next: Locale Categories,  Prev: Effects of Locale,  Up: Locales

7.2 Choosing a Locale
=====================

The simplest way for the user to choose a locale is to set the
environment variable ‘LANG’.  This specifies a single locale to use for
all purposes.  For example, a user could specify a hypothetical locale
named ‘espana-castellano’ to use the standard conventions of most of
Spain.

   The set of locales supported depends on the operating system you are
using, and so do their names, except that the standard locale called ‘C’
or ‘POSIX’ always exist.  *Note Locale Names::.

   In order to force the system to always use the default locale, the
user can set the ‘LC_ALL’ environment variable to ‘C’.

   A user also has the option of specifying different locales for
different purposes—in effect, choosing a mixture of multiple locales.
*Note Locale Categories::.

   For example, the user might specify the locale ‘espana-castellano’
for most purposes, but specify the locale ‘usa-english’ for currency
formatting.  This might make sense if the user is a Spanish-speaking
American, working in Spanish, but representing monetary amounts in US
dollars.

   Note that both locales ‘espana-castellano’ and ‘usa-english’, like
all locales, would include conventions for all of the purposes to which
locales apply.  However, the user can choose to use each locale for a
particular subset of those purposes.


File: libc.info,  Node: Locale Categories,  Next: Setting the Locale,  Prev: Choosing Locale,  Up: Locales

7.3 Locale Categories
=====================

The purposes that locales serve are grouped into “categories”, so that a
user or a program can choose the locale for each category independently.
Here is a table of categories; each name is both an environment variable
that a user can set, and a macro name that you can use as the first
argument to ‘setlocale’.

   The contents of the environment variable (or the string in the second
argument to ‘setlocale’) has to be a valid locale name.  *Note Locale
Names::.

‘LC_COLLATE’

     This category applies to collation of strings (functions ‘strcoll’
     and ‘strxfrm’); see *note Collation Functions::.

‘LC_CTYPE’

     This category applies to classification and conversion of
     characters, and to multibyte and wide characters; see *note
     Character Handling::, and *note Character Set Handling::.

‘LC_MONETARY’

     This category applies to formatting monetary values; see *note
     General Numeric::.

‘LC_NUMERIC’

     This category applies to formatting numeric values that are not
     monetary; see *note General Numeric::.

‘LC_TIME’

     This category applies to formatting date and time values; see *note
     Formatting Calendar Time::.

‘LC_MESSAGES’

     This category applies to selecting the language used in the user
     interface for message translation (*note The Uniforum approach::;
     *note Message catalogs a la X/Open::) and contains regular
     expressions for affirmative and negative responses.

‘LC_ALL’

     This is not a category; it is only a macro that you can use with
     ‘setlocale’ to set a single locale for all purposes.  Setting this
     environment variable overwrites all selections by the other ‘LC_*’
     variables or ‘LANG’.

‘LANG’

     If this environment variable is defined, its value specifies the
     locale to use for all purposes except as overridden by the
     variables above.

   When developing the message translation functions it was felt that
the functionality provided by the variables above is not sufficient.
For example, it should be possible to specify more than one locale name.
Take a Swedish user who better speaks German than English, and a program
whose messages are output in English by default.  It should be possible
to specify that the first choice of language is Swedish, the second
German, and if this also fails to use English.  This is possible with
the variable ‘LANGUAGE’.  For further description of this GNU extension
see *note Using gettextized software::.


File: libc.info,  Node: Setting the Locale,  Next: Standard Locales,  Prev: Locale Categories,  Up: Locales

7.4 How Programs Set the Locale
===============================

A C program inherits its locale environment variables when it starts up.
This happens automatically.  However, these variables do not
automatically control the locale used by the library functions, because
ISO C says that all programs start by default in the standard ‘C’
locale.  To use the locales specified by the environment, you must call
‘setlocale’.  Call it as follows:

     setlocale (LC_ALL, "");

to select a locale based on the user choice of the appropriate
environment variables.

   You can also use ‘setlocale’ to specify a particular locale, for
general use or for a specific category.

   The symbols in this section are defined in the header file
‘locale.h’.

 -- Function: char * setlocale (int CATEGORY, const char *LOCALE)

     Preliminary: | MT-Unsafe const:locale env | AS-Unsafe init lock
     heap corrupt | AC-Unsafe init corrupt lock mem fd | *Note POSIX
     Safety Concepts::.

     The function ‘setlocale’ sets the current locale for category
     CATEGORY to LOCALE.

     If CATEGORY is ‘LC_ALL’, this specifies the locale for all
     purposes.  The other possible values of CATEGORY specify a single
     purpose (*note Locale Categories::).

     You can also use this function to find out the current locale by
     passing a null pointer as the LOCALE argument.  In this case,
     ‘setlocale’ returns a string that is the name of the locale
     currently selected for category CATEGORY.

     The string returned by ‘setlocale’ can be overwritten by subsequent
     calls, so you should make a copy of the string (*note Copying
     Strings and Arrays::) if you want to save it past any further calls
     to ‘setlocale’.  (The standard library is guaranteed never to call
     ‘setlocale’ itself.)

     You should not modify the string returned by ‘setlocale’.  It might
     be the same string that was passed as an argument in a previous
     call to ‘setlocale’.  One requirement is that the CATEGORY must be
     the same in the call the string was returned and the one when the
     string is passed in as LOCALE parameter.

     When you read the current locale for category ‘LC_ALL’, the value
     encodes the entire combination of selected locales for all
     categories.  If you specify the same “locale name” with ‘LC_ALL’ in
     a subsequent call to ‘setlocale’, it restores the same combination
     of locale selections.

     To be sure you can use the returned string encoding the currently
     selected locale at a later time, you must make a copy of the
     string.  It is not guaranteed that the returned pointer remains
     valid over time.

     When the LOCALE argument is not a null pointer, the string returned
     by ‘setlocale’ reflects the newly-modified locale.

     If you specify an empty string for LOCALE, this means to read the
     appropriate environment variable and use its value to select the
     locale for CATEGORY.

     If a nonempty string is given for LOCALE, then the locale of that
     name is used if possible.

     The effective locale name (either the second argument to
     ‘setlocale’, or if the argument is an empty string, the name
     obtained from the process environment) must be a valid locale name.
     *Note Locale Names::.

     If you specify an invalid locale name, ‘setlocale’ returns a null
     pointer and leaves the current locale unchanged.

   Here is an example showing how you might use ‘setlocale’ to
temporarily switch to a new locale.

     #include <stddef.h>
     #include <locale.h>
     #include <stdlib.h>
     #include <string.h>

     void
     with_other_locale (char *new_locale,
                        void (*subroutine) (int),
                        int argument)
     {
       char *old_locale, *saved_locale;

       /* Get the name of the current locale.  */
       old_locale = setlocale (LC_ALL, NULL);

       /* Copy the name so it won’t be clobbered by ‘setlocale’. */
       saved_locale = strdup (old_locale);
       if (saved_locale == NULL)
         fatal ("Out of memory");

       /* Now change the locale and do some stuff with it. */
       setlocale (LC_ALL, new_locale);
       (*subroutine) (argument);

       /* Restore the original locale. */
       setlocale (LC_ALL, saved_locale);
       free (saved_locale);
     }

   *Portability Note:* Some ISO C systems may define additional locale
categories, and future versions of the library will do so.  For
portability, assume that any symbol beginning with ‘LC_’ might be
defined in ‘locale.h’.


File: libc.info,  Node: Standard Locales,  Next: Locale Names,  Prev: Setting the Locale,  Up: Locales

7.5 Standard Locales
====================

The only locale names you can count on finding on all operating systems
are these three standard ones:

‘"C"’
     This is the standard C locale.  The attributes and behavior it
     provides are specified in the ISO C standard.  When your program
     starts up, it initially uses this locale by default.

‘"POSIX"’
     This is the standard POSIX locale.  Currently, it is an alias for
     the standard C locale.

‘""’
     The empty name says to select a locale based on environment
     variables.  *Note Locale Categories::.

   Defining and installing named locales is normally a responsibility of
the system administrator at your site (or the person who installed the
GNU C Library).  It is also possible for the user to create private
locales.  All this will be discussed later when describing the tool to
do so.

   If your program needs to use something other than the ‘C’ locale, it
will be more portable if you use whatever locale the user specifies with
the environment, rather than trying to specify some non-standard locale
explicitly by name.  Remember, different machines might have different
sets of locales installed.


File: libc.info,  Node: Locale Names,  Next: Locale Information,  Prev: Standard Locales,  Up: Locales

7.6 Locale Names
================

The following command prints a list of locales supported by the system:

       locale -a

   *Portability Note:* With the notable exception of the standard locale
names ‘C’ and ‘POSIX’, locale names are system-specific.

   Most locale names follow XPG syntax and consist of up to four parts:

     LANGUAGE[_TERRITORY[.CODESET]][@MODIFIER]

   Beside the first part, all of them are allowed to be missing.  If the
full specified locale is not found, less specific ones are looked for.
The various parts will be stripped off, in the following order:

  1. codeset
  2. normalized codeset
  3. territory
  4. modifier

   For example, the locale name ‘de_AT.iso885915@euro’ denotes a
German-language locale for use in Austria, using the ISO-8859-15
(Latin-9) character set, and with the Euro as the currency symbol.

   In addition to locale names which follow XPG syntax, systems may
provide aliases such as ‘german’.  Both categories of names must not
contain the slash character ‘/’.

   If the locale name starts with a slash ‘/’, it is treated as a path
relative to the configured locale directories; see ‘LOCPATH’ below.  The
specified path must not contain a component ‘..’, or the name is
invalid, and ‘setlocale’ will fail.

   *Portability Note:* POSIX suggests that if a locale name starts with
a slash ‘/’, it is resolved as an absolute path.  However, the GNU C
Library treats it as a relative path under the directories listed in
‘LOCPATH’ (or the default locale directory if ‘LOCPATH’ is unset).

   Locale names which are longer than an implementation-defined limit
are invalid and cause ‘setlocale’ to fail.

   As a special case, locale names used with ‘LC_ALL’ can combine
several locales, reflecting different locale settings for different
categories.  For example, you might want to use a U.S. locale with ISO
A4 paper format, so you set ‘LANG’ to ‘en_US.UTF-8’, and ‘LC_PAPER’ to
‘de_DE.UTF-8’.  In this case, the ‘LC_ALL’-style combined locale name is

     LC_CTYPE=en_US.UTF-8;LC_TIME=en_US.UTF-8;LC_PAPER=de_DE.UTF-8;...

   followed by other category settings not shown here.

   The path used for finding locale data can be set using the ‘LOCPATH’
environment variable.  This variable lists the directories in which to
search for locale definitions, separated by a colon ‘:’.

   The default path for finding locale data is system specific.  A
typical value for the ‘LOCPATH’ default is:

     /usr/share/locale

   The value of ‘LOCPATH’ is ignored by privileged programs for security
reasons, and only the default directory is used.


File: libc.info,  Node: Locale Information,  Next: Formatting Numbers,  Prev: Locale Names,  Up: Locales

7.7 Accessing Locale Information
================================

There are several ways to access locale information.  The simplest way
is to let the C library itself do the work.  Several of the functions in
this library implicitly access the locale data, and use what information
is provided by the currently selected locale.  This is how the locale
model is meant to work normally.

   As an example take the ‘strftime’ function, which is meant to nicely
format date and time information (*note Formatting Calendar Time::).
Part of the standard information contained in the ‘LC_TIME’ category is
the names of the months.  Instead of requiring the programmer to take
care of providing the translations the ‘strftime’ function does this all
by itself.  ‘%A’ in the format string is replaced by the appropriate
weekday name of the locale currently selected by ‘LC_TIME’.  This is an
easy example, and wherever possible functions do things automatically in
this way.

   But there are quite often situations when there is simply no function
to perform the task, or it is simply not possible to do the work
automatically.  For these cases it is necessary to access the
information in the locale directly.  To do this the C library provides
two functions: ‘localeconv’ and ‘nl_langinfo’.  The former is part of
ISO C and therefore portable, but has a brain-damaged interface.  The
second is part of the Unix interface and is portable in as far as the
system follows the Unix standards.

* Menu:

* The Lame Way to Locale Data::   ISO C’s ‘localeconv’.
* The Elegant and Fast Way::      X/Open’s ‘nl_langinfo’.


File: libc.info,  Node: The Lame Way to Locale Data,  Next: The Elegant and Fast Way,  Up: Locale Information

7.7.1 ‘localeconv’: It is portable but ...
------------------------------------------

Together with the ‘setlocale’ function the ISO C people invented the
‘localeconv’ function.  It is a masterpiece of poor design.  It is
expensive to use, not extensible, and not generally usable as it
provides access to only ‘LC_MONETARY’ and ‘LC_NUMERIC’ related
information.  Nevertheless, if it is applicable to a given situation it
should be used since it is very portable.  The function ‘strfmon’
formats monetary amounts according to the selected locale using this
information.

 -- Function: struct lconv * localeconv (void)

     Preliminary: | MT-Unsafe race:localeconv locale | AS-Unsafe |
     AC-Safe | *Note POSIX Safety Concepts::.

     The ‘localeconv’ function returns a pointer to a structure whose
     components contain information about how numeric and monetary
     values should be formatted in the current locale.

     You should not modify the structure or its contents.  The structure
     might be overwritten by subsequent calls to ‘localeconv’, or by
     calls to ‘setlocale’, but no other function in the library
     overwrites this value.

 -- Data Type: struct lconv

     ‘localeconv’’s return value is of this data type.  Its elements are
     described in the following subsections.

   If a member of the structure ‘struct lconv’ has type ‘char’, and the
value is ‘CHAR_MAX’, it means that the current locale has no value for
that parameter.

* Menu:

* General Numeric::             Parameters for formatting numbers and
                                 currency amounts.
* Currency Symbol::             How to print the symbol that identifies an
                                 amount of money (e.g. ‘$’).
* Sign of Money Amount::        How to print the (positive or negative) sign
                                 for a monetary amount, if one exists.


File: libc.info,  Node: General Numeric,  Next: Currency Symbol,  Up: The Lame Way to Locale Data

7.7.1.1 Generic Numeric Formatting Parameters
.............................................

These are the standard members of ‘struct lconv’; there may be others.

‘char *decimal_point’
‘char *mon_decimal_point’
     These are the decimal-point separators used in formatting
     non-monetary and monetary quantities, respectively.  In the ‘C’
     locale, the value of ‘decimal_point’ is ‘"."’, and the value of
     ‘mon_decimal_point’ is ‘""’.

‘char *thousands_sep’
‘char *mon_thousands_sep’
     These are the separators used to delimit groups of digits to the
     left of the decimal point in formatting non-monetary and monetary
     quantities, respectively.  In the ‘C’ locale, both members have a
     value of ‘""’ (the empty string).

‘char *grouping’
‘char *mon_grouping’
     These are strings that specify how to group the digits to the left
     of the decimal point.  ‘grouping’ applies to non-monetary
     quantities and ‘mon_grouping’ applies to monetary quantities.  Use
     either ‘thousands_sep’ or ‘mon_thousands_sep’ to separate the digit
     groups.

     Each member of these strings is to be interpreted as an integer
     value of type ‘char’.  Successive numbers (from left to right) give
     the sizes of successive groups (from right to left, starting at the
     decimal point.)  The last member is either ‘0’, in which case the
     previous member is used over and over again for all the remaining
     groups, or ‘CHAR_MAX’, in which case there is no more grouping—or,
     put another way, any remaining digits form one large group without
     separators.

     For example, if ‘grouping’ is ‘"\04\03\02"’, the correct grouping
     for the number ‘123456787654321’ is ‘12’, ‘34’, ‘56’, ‘78’, ‘765’,
     ‘4321’.  This uses a group of 4 digits at the end, preceded by a
     group of 3 digits, preceded by groups of 2 digits (as many as
     needed).  With a separator of ‘,’, the number would be printed as
     ‘12,34,56,78,765,4321’.

     A value of ‘"\03"’ indicates repeated groups of three digits, as
     normally used in the U.S.

     In the standard ‘C’ locale, both ‘grouping’ and ‘mon_grouping’ have
     a value of ‘""’.  This value specifies no grouping at all.

‘char int_frac_digits’
‘char frac_digits’
     These are small integers indicating how many fractional digits (to
     the right of the decimal point) should be displayed in a monetary
     value in international and local formats, respectively.  (Most
     often, both members have the same value.)

     In the standard ‘C’ locale, both of these members have the value
     ‘CHAR_MAX’, meaning “unspecified”.  The ISO standard doesn’t say
     what to do when you find this value; we recommend printing no
     fractional digits.  (This locale also specifies the empty string
     for ‘mon_decimal_point’, so printing any fractional digits would be
     confusing!)


File: libc.info,  Node: Currency Symbol,  Next: Sign of Money Amount,  Prev: General Numeric,  Up: The Lame Way to Locale Data

7.7.1.2 Printing the Currency Symbol
....................................

These members of the ‘struct lconv’ structure specify how to print the
symbol to identify a monetary value—the international analog of ‘$’ for
US dollars.

   Each country has two standard currency symbols.  The “local currency
symbol” is used commonly within the country, while the “international
currency symbol” is used internationally to refer to that country’s
currency when it is necessary to indicate the country unambiguously.

   For example, many countries use the dollar as their monetary unit,
and when dealing with international currencies it’s important to specify
that one is dealing with (say) Canadian dollars instead of U.S. dollars
or Australian dollars.  But when the context is known to be Canada,
there is no need to make this explicit—dollar amounts are implicitly
assumed to be in Canadian dollars.

‘char *currency_symbol’
     The local currency symbol for the selected locale.

     In the standard ‘C’ locale, this member has a value of ‘""’ (the
     empty string), meaning “unspecified”.  The ISO standard doesn’t say
     what to do when you find this value; we recommend you simply print
     the empty string as you would print any other string pointed to by
     this variable.

‘char *int_curr_symbol’
     The international currency symbol for the selected locale.

     The value of ‘int_curr_symbol’ should normally consist of a
     three-letter abbreviation determined by the international standard
     ‘ISO 4217 Codes for the Representation of Currency and Funds’,
     followed by a one-character separator (often a space).

     In the standard ‘C’ locale, this member has a value of ‘""’ (the
     empty string), meaning “unspecified”.  We recommend you simply
     print the empty string as you would print any other string pointed
     to by this variable.

‘char p_cs_precedes’
‘char n_cs_precedes’
‘char int_p_cs_precedes’
‘char int_n_cs_precedes’
     These members are ‘1’ if the ‘currency_symbol’ or ‘int_curr_symbol’
     strings should precede the value of a monetary amount, or ‘0’ if
     the strings should follow the value.  The ‘p_cs_precedes’ and
     ‘int_p_cs_precedes’ members apply to positive amounts (or zero),
     and the ‘n_cs_precedes’ and ‘int_n_cs_precedes’ members apply to
     negative amounts.

     In the standard ‘C’ locale, all of these members have a value of
     ‘CHAR_MAX’, meaning “unspecified”.  The ISO standard doesn’t say
     what to do when you find this value.  We recommend printing the
     currency symbol before the amount, which is right for most
     countries.  In other words, treat all nonzero values alike in these
     members.

     The members with the ‘int_’ prefix apply to the ‘int_curr_symbol’
     while the other two apply to ‘currency_symbol’.

‘char p_sep_by_space’
‘char n_sep_by_space’
‘char int_p_sep_by_space’
‘char int_n_sep_by_space’
     These members are ‘1’ if a space should appear between the
     ‘currency_symbol’ or ‘int_curr_symbol’ strings and the amount, or
     ‘0’ if no space should appear.  The ‘p_sep_by_space’ and
     ‘int_p_sep_by_space’ members apply to positive amounts (or zero),
     and the ‘n_sep_by_space’ and ‘int_n_sep_by_space’ members apply to
     negative amounts.

     In the standard ‘C’ locale, all of these members have a value of
     ‘CHAR_MAX’, meaning “unspecified”.  The ISO standard doesn’t say
     what you should do when you find this value; we suggest you treat
     it as 1 (print a space).  In other words, treat all nonzero values
     alike in these members.

     The members with the ‘int_’ prefix apply to the ‘int_curr_symbol’
     while the other two apply to ‘currency_symbol’.  There is one
     specialty with the ‘int_curr_symbol’, though.  Since all legal
     values contain a space at the end of the string one either prints
     this space (if the currency symbol must appear in front and must be
     separated) or one has to avoid printing this character at all
     (especially when at the end of the string).


File: libc.info,  Node: Sign of Money Amount,  Prev: Currency Symbol,  Up: The Lame Way to Locale Data

7.7.1.3 Printing the Sign of a Monetary Amount
..............................................

These members of the ‘struct lconv’ structure specify how to print the
sign (if any) of a monetary value.

‘char *positive_sign’
‘char *negative_sign’
     These are strings used to indicate positive (or zero) and negative
     monetary quantities, respectively.

     In the standard ‘C’ locale, both of these members have a value of
     ‘""’ (the empty string), meaning “unspecified”.

     The ISO standard doesn’t say what to do when you find this value;
     we recommend printing ‘positive_sign’ as you find it, even if it is
     empty.  For a negative value, print ‘negative_sign’ as you find it
     unless both it and ‘positive_sign’ are empty, in which case print
     ‘-’ instead.  (Failing to indicate the sign at all seems rather
     unreasonable.)

‘char p_sign_posn’
‘char n_sign_posn’
‘char int_p_sign_posn’
‘char int_n_sign_posn’
     These members are small integers that indicate how to position the
     sign for nonnegative and negative monetary quantities,
     respectively.  (The string used for the sign is what was specified
     with ‘positive_sign’ or ‘negative_sign’.)  The possible values are
     as follows:

     ‘0’
          The currency symbol and quantity should be surrounded by
          parentheses.

     ‘1’
          Print the sign string before the quantity and currency symbol.

     ‘2’
          Print the sign string after the quantity and currency symbol.

     ‘3’
          Print the sign string right before the currency symbol.

     ‘4’
          Print the sign string right after the currency symbol.

     ‘CHAR_MAX’
          “Unspecified”.  Both members have this value in the standard
          ‘C’ locale.

     The ISO standard doesn’t say what you should do when the value is
     ‘CHAR_MAX’.  We recommend you print the sign after the currency
     symbol.

     The members with the ‘int_’ prefix apply to the ‘int_curr_symbol’
     while the other two apply to ‘currency_symbol’.


File: libc.info,  Node: The Elegant and Fast Way,  Prev: The Lame Way to Locale Data,  Up: Locale Information

7.7.2 Pinpoint Access to Locale Data
------------------------------------

When writing the X/Open Portability Guide the authors realized that the
‘localeconv’ function is not enough to provide reasonable access to
locale information.  The information which was meant to be available in
the locale (as later specified in the POSIX.1 standard) requires more
ways to access it.  Therefore the ‘nl_langinfo’ function was introduced.

 -- Function: char * nl_langinfo (nl_item ITEM)

     Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     The ‘nl_langinfo’ function can be used to access individual
     elements of the locale categories.  Unlike the ‘localeconv’
     function, which returns all the information, ‘nl_langinfo’ lets the
     caller select what information it requires.  This is very fast and
     it is not a problem to call this function multiple times.

     A second advantage is that in addition to the numeric and monetary
     formatting information, information from the ‘LC_TIME’ and
     ‘LC_MESSAGES’ categories is available.

     The type ‘nl_item’ is defined in ‘nl_types.h’.  The argument ITEM
     is a numeric value defined in the header ‘langinfo.h’.  The X/Open
     standard defines the following values:

     ‘CODESET’
          ‘nl_langinfo’ returns a string with the name of the coded
          character set used in the selected locale.

     ‘ABDAY_1’
     ‘ABDAY_2’
     ‘ABDAY_3’
     ‘ABDAY_4’
     ‘ABDAY_5’
     ‘ABDAY_6’
     ‘ABDAY_7’
          ‘nl_langinfo’ returns the abbreviated weekday name.  ‘ABDAY_1’
          corresponds to Sunday.
     ‘DAY_1’
     ‘DAY_2’
     ‘DAY_3’
     ‘DAY_4’
     ‘DAY_5’
     ‘DAY_6’
     ‘DAY_7’
          Similar to ‘ABDAY_1’, etc., but here the return value is the
          unabbreviated weekday name.
     ‘ABMON_1’
     ‘ABMON_2’
     ‘ABMON_3’
     ‘ABMON_4’
     ‘ABMON_5’
     ‘ABMON_6’
     ‘ABMON_7’
     ‘ABMON_8’
     ‘ABMON_9’
     ‘ABMON_10’
     ‘ABMON_11’
     ‘ABMON_12’
          The return value is the abbreviated name of the month, in the
          grammatical form used when the month forms part of a complete
          date.  ‘ABMON_1’ corresponds to January.
     ‘MON_1’
     ‘MON_2’
     ‘MON_3’
     ‘MON_4’
     ‘MON_5’
     ‘MON_6’
     ‘MON_7’
     ‘MON_8’
     ‘MON_9’
     ‘MON_10’
     ‘MON_11’
     ‘MON_12’
          Similar to ‘ABMON_1’, etc., but here the month names are not
          abbreviated.  Here the first value ‘MON_1’ also corresponds to
          January.
     ‘ALTMON_1’
     ‘ALTMON_2’
     ‘ALTMON_3’
     ‘ALTMON_4’
     ‘ALTMON_5’
     ‘ALTMON_6’
     ‘ALTMON_7’
     ‘ALTMON_8’
     ‘ALTMON_9’
     ‘ALTMON_10’
     ‘ALTMON_11’
     ‘ALTMON_12’
          Similar to ‘MON_1’, etc., but here the month names are in the
          grammatical form used when the month is named by itself.  The
          ‘strftime’ functions use these month names for the conversion
          specifier ‘%OB’ (*note Formatting Calendar Time::).

          Note that not all languages need two different forms of the
          month names, so the strings returned for ‘MON_...’ and
          ‘ALTMON_...’ may or may not be the same, depending on the
          locale.

          *NB:* ‘ABALTMON_...’ constants corresponding to the ‘%Ob’
          conversion specifier are not currently provided, but are
          expected to be in a future release.  In the meantime, it is
          possible to use ‘_NL_ABALTMON_...’.
     ‘AM_STR’
     ‘PM_STR’
          The return values are strings which can be used in the
          representation of time as an hour from 1 to 12 plus an am/pm
          specifier.

          Note that in locales which do not use this time representation
          these strings might be empty, in which case the am/pm format
          cannot be used at all.
     ‘D_T_FMT’
          The return value can be used as a format string for ‘strftime’
          to represent time and date in a locale-specific way.
     ‘D_FMT’
          The return value can be used as a format string for ‘strftime’
          to represent a date in a locale-specific way.
     ‘T_FMT’
          The return value can be used as a format string for ‘strftime’
          to represent time in a locale-specific way.
     ‘T_FMT_AMPM’
          The return value can be used as a format string for ‘strftime’
          to represent time in the am/pm format.

          Note that if the am/pm format does not make any sense for the
          selected locale, the return value might be the same as the one
          for ‘T_FMT’.
     ‘ERA’
          The return value represents the era used in the current
          locale.

          Most locales do not define this value.  An example of a locale
          which does define this value is the Japanese one.  In Japan,
          the traditional representation of dates includes the name of
          the era corresponding to the then-emperor’s reign.

          Normally it should not be necessary to use this value
          directly.  Specifying the ‘E’ modifier in their format strings
          causes the ‘strftime’ functions to use this information.  The
          format of the returned string is not specified, and therefore
          you should not assume knowledge of it on different systems.
     ‘ERA_YEAR’
          The return value gives the year in the relevant era of the
          locale.  As for ‘ERA’ it should not be necessary to use this
          value directly.
     ‘ERA_D_T_FMT’
          This return value can be used as a format string for
          ‘strftime’ to represent dates and times in a locale-specific
          era-based way.
     ‘ERA_D_FMT’
          This return value can be used as a format string for
          ‘strftime’ to represent a date in a locale-specific era-based
          way.
     ‘ERA_T_FMT’
          This return value can be used as a format string for
          ‘strftime’ to represent time in a locale-specific era-based
          way.
     ‘ALT_DIGITS’
          The return value is a representation of up to 100 values used
          to represent the values 0 to 99.  As for ‘ERA’ this value is
          not intended to be used directly, but instead indirectly
          through the ‘strftime’ function.  When the modifier ‘O’ is
          used in a format which would otherwise use numerals to
          represent hours, minutes, seconds, weekdays, months, or weeks,
          the appropriate value for the locale is used instead.
     ‘INT_CURR_SYMBOL’
          The same as the value returned by ‘localeconv’ in the
          ‘int_curr_symbol’ element of the ‘struct lconv’.
     ‘CURRENCY_SYMBOL’
     ‘CRNCYSTR’
          The same as the value returned by ‘localeconv’ in the
          ‘currency_symbol’ element of the ‘struct lconv’.

          ‘CRNCYSTR’ is a deprecated alias still required by Unix98.
     ‘MON_DECIMAL_POINT’
          The same as the value returned by ‘localeconv’ in the
          ‘mon_decimal_point’ element of the ‘struct lconv’.
     ‘MON_THOUSANDS_SEP’
          The same as the value returned by ‘localeconv’ in the
          ‘mon_thousands_sep’ element of the ‘struct lconv’.
     ‘MON_GROUPING’
          The same as the value returned by ‘localeconv’ in the
          ‘mon_grouping’ element of the ‘struct lconv’.
     ‘POSITIVE_SIGN’
          The same as the value returned by ‘localeconv’ in the
          ‘positive_sign’ element of the ‘struct lconv’.
     ‘NEGATIVE_SIGN’
          The same as the value returned by ‘localeconv’ in the
          ‘negative_sign’ element of the ‘struct lconv’.
     ‘INT_FRAC_DIGITS’
          The same as the value returned by ‘localeconv’ in the
          ‘int_frac_digits’ element of the ‘struct lconv’.
     ‘FRAC_DIGITS’
          The same as the value returned by ‘localeconv’ in the
          ‘frac_digits’ element of the ‘struct lconv’.
     ‘P_CS_PRECEDES’
          The same as the value returned by ‘localeconv’ in the
          ‘p_cs_precedes’ element of the ‘struct lconv’.
     ‘P_SEP_BY_SPACE’
          The same as the value returned by ‘localeconv’ in the
          ‘p_sep_by_space’ element of the ‘struct lconv’.
     ‘N_CS_PRECEDES’
          The same as the value returned by ‘localeconv’ in the
          ‘n_cs_precedes’ element of the ‘struct lconv’.
     ‘N_SEP_BY_SPACE’
          The same as the value returned by ‘localeconv’ in the
          ‘n_sep_by_space’ element of the ‘struct lconv’.
     ‘P_SIGN_POSN’
          The same as the value returned by ‘localeconv’ in the
          ‘p_sign_posn’ element of the ‘struct lconv’.
     ‘N_SIGN_POSN’
          The same as the value returned by ‘localeconv’ in the
          ‘n_sign_posn’ element of the ‘struct lconv’.

     ‘INT_P_CS_PRECEDES’
          The same as the value returned by ‘localeconv’ in the
          ‘int_p_cs_precedes’ element of the ‘struct lconv’.
     ‘INT_P_SEP_BY_SPACE’
          The same as the value returned by ‘localeconv’ in the
          ‘int_p_sep_by_space’ element of the ‘struct lconv’.
     ‘INT_N_CS_PRECEDES’
          The same as the value returned by ‘localeconv’ in the
          ‘int_n_cs_precedes’ element of the ‘struct lconv’.
     ‘INT_N_SEP_BY_SPACE’
          The same as the value returned by ‘localeconv’ in the
          ‘int_n_sep_by_space’ element of the ‘struct lconv’.
     ‘INT_P_SIGN_POSN’
          The same as the value returned by ‘localeconv’ in the
          ‘int_p_sign_posn’ element of the ‘struct lconv’.
     ‘INT_N_SIGN_POSN’
          The same as the value returned by ‘localeconv’ in the
          ‘int_n_sign_posn’ element of the ‘struct lconv’.

     ‘DECIMAL_POINT’
     ‘RADIXCHAR’
          The same as the value returned by ‘localeconv’ in the
          ‘decimal_point’ element of the ‘struct lconv’.

          The name ‘RADIXCHAR’ is a deprecated alias still used in
          Unix98.
     ‘THOUSANDS_SEP’
     ‘THOUSEP’
          The same as the value returned by ‘localeconv’ in the
          ‘thousands_sep’ element of the ‘struct lconv’.

          The name ‘THOUSEP’ is a deprecated alias still used in Unix98.
     ‘GROUPING’
          The same as the value returned by ‘localeconv’ in the
          ‘grouping’ element of the ‘struct lconv’.
     ‘YESEXPR’
          The return value is a regular expression which can be used
          with the ‘regex’ function to recognize a positive response to
          a yes/no question.  The GNU C Library provides the ‘rpmatch’
          function for easier handling in applications.
     ‘NOEXPR’
          The return value is a regular expression which can be used
          with the ‘regex’ function to recognize a negative response to
          a yes/no question.
     ‘YESSTR’
          The return value is a locale-specific translation of the
          positive response to a yes/no question.

          Using this value is deprecated since it is a very special case
          of message translation, and is better handled by the message
          translation functions (*note Message Translation::).

          The use of this symbol is deprecated.  Instead message
          translation should be used.
     ‘NOSTR’
          The return value is a locale-specific translation of the
          negative response to a yes/no question.  What is said for
          ‘YESSTR’ is also true here.

          The use of this symbol is deprecated.  Instead message
          translation should be used.

     The file ‘langinfo.h’ defines a lot more symbols but none of them
     are official.  Using them is not portable, and the format of the
     return values might change.  Therefore we recommended you not use
     them.

     Note that the return value for any valid argument can be used in
     all situations (with the possible exception of the am/pm time
     formatting codes).  If the user has not selected any locale for the
     appropriate category, ‘nl_langinfo’ returns the information from
     the ‘"C"’ locale.  It is therefore possible to use this function as
     shown in the example below.

     If the argument ITEM is not valid, a pointer to an empty string is
     returned.

   An example of ‘nl_langinfo’ usage is a function which has to print a
given date and time in a locale-specific way.  At first one might think
that, since ‘strftime’ internally uses the locale information, writing
something like the following is enough:

     size_t
     i18n_time_n_data (char *s, size_t len, const struct tm *tp)
     {
       return strftime (s, len, "%X %D", tp);
     }

   The format contains no weekday or month names and therefore is
internationally usable.  Wrong!  The output produced is something like
‘"hh:mm:ss MM/DD/YY"’.  This format is only recognizable in the USA.
Other countries use different formats.  Therefore the function should be
rewritten like this:

     size_t
     i18n_time_n_data (char *s, size_t len, const struct tm *tp)
     {
       return strftime (s, len, nl_langinfo (D_T_FMT), tp);
     }

   Now it uses the date and time format of the locale selected when the
program runs.  If the user selects the locale correctly there should
never be a misunderstanding over the time and date format.


File: libc.info,  Node: Formatting Numbers,  Next: Yes-or-No Questions,  Prev: Locale Information,  Up: Locales

7.8 A dedicated function to format numbers
==========================================

We have seen that the structure returned by ‘localeconv’ as well as the
values given to ‘nl_langinfo’ allow you to retrieve the various pieces
of locale-specific information to format numbers and monetary amounts.
We have also seen that the underlying rules are quite complex.

   Therefore the X/Open standards introduce a function which uses such
locale information, making it easier for the user to format numbers
according to these rules.

 -- Function: ssize_t strfmon (char *S, size_t MAXSIZE, const char
          *FORMAT, ...)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘strfmon’ function is similar to the ‘strftime’ function in
     that it takes a buffer, its size, a format string, and values to
     write into the buffer as text in a form specified by the format
     string.  Like ‘strftime’, the function also returns the number of
     bytes written into the buffer.

     There are two differences: ‘strfmon’ can take more than one
     argument, and, of course, the format specification is different.
     Like ‘strftime’, the format string consists of normal text, which
     is output as is, and format specifiers, which are indicated by a
     ‘%’.  Immediately after the ‘%’, you can optionally specify various
     flags and formatting information before the main formatting
     character, in a similar way to ‘printf’:

        • Immediately following the ‘%’ there can be one or more of the
          following flags:
          ‘=F’
               The single byte character F is used for this field as the
               numeric fill character.  By default this character is a
               space character.  Filling with this character is only
               performed if a left precision is specified.  It is not
               just to fill to the given field width.
          ‘^’
               The number is printed without grouping the digits
               according to the rules of the current locale.  By default
               grouping is enabled.
          ‘+’, ‘(’
               At most one of these flags can be used.  They select
               which format to represent the sign of a currency amount.
               By default, and if ‘+’ is given, the locale equivalent of
               +/- is used.  If ‘(’ is given, negative amounts are
               enclosed in parentheses.  The exact format is determined
               by the values of the ‘LC_MONETARY’ category of the locale
               selected at program runtime.
          ‘!’
               The output will not contain the currency symbol.
          ‘-’
               The output will be formatted left-justified instead of
               right-justified if it does not fill the entire field
               width.

     The next part of the specification is an optional field width.  If
     no width is specified 0 is taken.  During output, the function
     first determines how much space is required.  If it requires at
     least as many characters as given by the field width, it is output
     using as much space as necessary.  Otherwise, it is extended to use
     the full width by filling with the space character.  The presence
     or absence of the ‘-’ flag determines the side at which such
     padding occurs.  If present, the spaces are added at the right
     making the output left-justified, and vice versa.

     So far the format looks familiar, being similar to the ‘printf’ and
     ‘strftime’ formats.  However, the next two optional fields
     introduce something new.  The first one is a ‘#’ character followed
     by a decimal digit string.  The value of the digit string specifies
     the number of _digit_ positions to the left of the decimal point
     (or equivalent).  This does _not_ include the grouping character
     when the ‘^’ flag is not given.  If the space needed to print the
     number does not fill the whole width, the field is padded at the
     left side with the fill character, which can be selected using the
     ‘=’ flag and by default is a space.  For example, if the field
     width is selected as 6 and the number is 123, the fill character is
     ‘*’ the result will be ‘***123’.

     The second optional field starts with a ‘.’ (period) and consists
     of another decimal digit string.  Its value describes the number of
     characters printed after the decimal point.  The default is
     selected from the current locale (‘frac_digits’, ‘int_frac_digits’,
     see *note General Numeric::).  If the exact representation needs
     more digits than given by the field width, the displayed value is
     rounded.  If the number of fractional digits is selected to be
     zero, no decimal point is printed.

     As a GNU extension, the ‘strfmon’ implementation in the GNU C
     Library allows an optional ‘L’ next as a format modifier.  If this
     modifier is given, the argument is expected to be a ‘long double’
     instead of a ‘double’ value.

     Finally, the last component is a format specifier.  There are three
     specifiers defined:

     ‘i’
          Use the locale’s rules for formatting an international
          currency value.
     ‘n’
          Use the locale’s rules for formatting a national currency
          value.
     ‘%’
          Place a ‘%’ in the output.  There must be no flag, width
          specifier or modifier given, only ‘%%’ is allowed.

     As for ‘printf’, the function reads the format string from left to
     right and uses the values passed to the function following the
     format string.  The values are expected to be either of type
     ‘double’ or ‘long double’, depending on the presence of the
     modifier ‘L’.  The result is stored in the buffer pointed to by S.
     At most MAXSIZE characters are stored.

     The return value of the function is the number of characters stored
     in S, including the terminating ‘NULL’ byte.  If the number of
     characters stored would exceed MAXSIZE, the function returns -1 and
     the content of the buffer S is unspecified.  In this case ‘errno’
     is set to ‘E2BIG’.

   A few examples should make clear how the function works.  It is
assumed that all the following pieces of code are executed in a program
which uses the USA locale (‘en_US’).  The simplest form of the format is
this:

     strfmon (buf, 100, "@%n@%n@%n@", 123.45, -567.89, 12345.678);

The output produced is
     "@$123.45@-$567.89@$12,345.68@"

   We can notice several things here.  First, the widths of the output
numbers are different.  We have not specified a width in the format
string, and so this is no wonder.  Second, the third number is printed
using thousands separators.  The thousands separator for the ‘en_US’
locale is a comma.  The number is also rounded.  .678 is rounded to .68
since the format does not specify a precision and the default value in
the locale is 2.  Finally, note that the national currency symbol is
printed since ‘%n’ was used, not ‘i’.  The next example shows how we can
align the output.

     strfmon (buf, 100, "@%=*11n@%=*11n@%=*11n@", 123.45, -567.89, 12345.678);

The output this time is:

     "@    $123.45@   -$567.89@ $12,345.68@"

   Two things stand out.  Firstly, all fields have the same width
(eleven characters) since this is the width given in the format and
since no number required more characters to be printed.  The second
important point is that the fill character is not used.  This is correct
since the white space was not used to achieve a precision given by a ‘#’
modifier, but instead to fill to the given width.  The difference
becomes obvious if we now add a width specification.

     strfmon (buf, 100, "@%=*11#5n@%=*11#5n@%=*11#5n@",
              123.45, -567.89, 12345.678);

The output is

     "@ $***123.45@-$***567.89@ $12,456.68@"

   Here we can see that all the currency symbols are now aligned, and
that the space between the currency sign and the number is filled with
the selected fill character.  Note that although the width is selected
to be 5 and 123.45 has three digits left of the decimal point, the space
is filled with three asterisks.  This is correct since, as explained
above, the width does not include the positions used to store thousands
separators.  One last example should explain the remaining
functionality.

     strfmon (buf, 100, "@%=0(16#5.3i@%=0(16#5.3i@%=0(16#5.3i@",
              123.45, -567.89, 12345.678);

This rather complex format string produces the following output:

     "@ USD 000123,450 @(USD 000567.890)@ USD 12,345.678 @"

   The most noticeable change is the alternative way of representing
negative numbers.  In financial circles this is often done using
parentheses, and this is what the ‘(’ flag selected.  The fill character
is now ‘0’.  Note that this ‘0’ character is not regarded as a numeric
zero, and therefore the first and second numbers are not printed using a
thousands separator.  Since we used the format specifier ‘i’ instead of
‘n’, the international form of the currency symbol is used.  This is a
four letter string, in this case ‘"USD "’.  The last point is that since
the precision right of the decimal point is selected to be three, the
first and second numbers are printed with an extra zero at the end and
the third number is printed without rounding.


File: libc.info,  Node: Yes-or-No Questions,  Prev: Formatting Numbers,  Up: Locales

7.9 Yes-or-No Questions
=======================

Some non GUI programs ask a yes-or-no question.  If the messages
(especially the questions) are translated into foreign languages, be
sure that you localize the answers too.  It would be very bad habit to
ask a question in one language and request the answer in another, often
English.

   The GNU C Library contains ‘rpmatch’ to give applications easy access
to the corresponding locale definitions.

 -- Function: int rpmatch (const char *RESPONSE)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The function ‘rpmatch’ checks the string in RESPONSE for whether or
     not it is a correct yes-or-no answer and if yes, which one.  The
     check uses the ‘YESEXPR’ and ‘NOEXPR’ data in the ‘LC_MESSAGES’
     category of the currently selected locale.  The return value is as
     follows:

     ‘1’
          The user entered an affirmative answer.

     ‘0’
          The user entered a negative answer.

     ‘-1’
          The answer matched neither the ‘YESEXPR’ nor the ‘NOEXPR’
          regular expression.

     This function is not standardized but available beside in the GNU C
     Library at least also in the IBM AIX library.

This function would normally be used like this:

       ...
       /* Use a safe default.  */
       _Bool doit = false;

       fputs (gettext ("Do you really want to do this? "), stdout);
       fflush (stdout);
       /* Prepare the ‘getline’ call.  */
       line = NULL;
       len = 0;
       while (getline (&line, &len, stdin) >= 0)
         {
           /* Check the response.  */
           int res = rpmatch (line);
           if (res >= 0)
             {
               /* We got a definitive answer.  */
               if (res > 0)
                 doit = true;
               break;
             }
         }
       /* Free what ‘getline’ allocated.  */
       free (line);

   Note that the loop continues until a read error is detected or until
a definitive (positive or negative) answer is read.


File: libc.info,  Node: Message Translation,  Next: Searching and Sorting,  Prev: Locales,  Up: Top

8 Message Translation
*********************

The program’s interface with the user should be designed to ease the
user’s task.  One way to ease the user’s task is to use messages in
whatever language the user prefers.

   Printing messages in different languages can be implemented in
different ways.  One could add all the different languages in the source
code and choose among the variants every time a message has to be
printed.  This is certainly not a good solution since extending the set
of languages is cumbersome (the code must be changed) and the code
itself can become really big with dozens of message sets.

   A better solution is to keep the message sets for each language in
separate files which are loaded at runtime depending on the language
selection of the user.

   The GNU C Library provides two different sets of functions to support
message translation.  The problem is that neither of the interfaces is
officially defined by the POSIX standard.  The ‘catgets’ family of
functions is defined in the X/Open standard but this is derived from
industry decisions and therefore not necessarily based on reasonable
decisions.

   As mentioned above, the message catalog handling provides easy
extendability by using external data files which contain the message
translations.  I.e., these files contain for each of the messages used
in the program a translation for the appropriate language.  So the tasks
of the message handling functions are

   • locate the external data file with the appropriate translations
   • load the data and make it possible to address the messages
   • map a given key to the translated message

   The two approaches mainly differ in the implementation of this last
step.  Decisions made in the last step influence the rest of the design.

* Menu:

* Message catalogs a la X/Open::  The ‘catgets’ family of functions.
* The Uniforum approach::         The ‘gettext’ family of functions.


File: libc.info,  Node: Message catalogs a la X/Open,  Next: The Uniforum approach,  Up: Message Translation

8.1 X/Open Message Catalog Handling
===================================

The ‘catgets’ functions are based on the simple scheme:

     Associate every message to translate in the source code with a
     unique identifier.  To retrieve a message from a catalog file
     solely the identifier is used.

   This means for the author of the program that s/he will have to make
sure the meaning of the identifier in the program code and in the
message catalogs is always the same.

   Before a message can be translated the catalog file must be located.
The user of the program must be able to guide the responsible function
to find whatever catalog the user wants.  This is separated from what
the programmer had in mind.

   All the types, constants and functions for the ‘catgets’ functions
are defined/declared in the ‘nl_types.h’ header file.

* Menu:

* The catgets Functions::      The ‘catgets’ function family.
* The message catalog files::  Format of the message catalog files.
* The gencat program::         How to generate message catalogs files which
                                can be used by the functions.
* Common Usage::               How to use the ‘catgets’ interface.


File: libc.info,  Node: The catgets Functions,  Next: The message catalog files,  Up: Message catalogs a la X/Open

8.1.1 The ‘catgets’ function family
-----------------------------------

 -- Function: nl_catd catopen (const char *CAT_NAME, int FLAG)

     Preliminary: | MT-Safe env | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     The ‘catopen’ function tries to locate the message data file named
     CAT_NAME and loads it when found.  The return value is of an opaque
     type and can be used in calls to the other functions to refer to
     this loaded catalog.

     The return value is ‘(nl_catd) -1’ in case the function failed and
     no catalog was loaded.  The global variable ‘errno’ contains a code
     for the error causing the failure.  But even if the function call
     succeeded this does not mean that all messages can be translated.

     Locating the catalog file must happen in a way which lets the user
     of the program influence the decision.  It is up to the user to
     decide about the language to use and sometimes it is useful to use
     alternate catalog files.  All this can be specified by the user by
     setting some environment variables.

     The first problem is to find out where all the message catalogs are
     stored.  Every program could have its own place to keep all the
     different files but usually the catalog files are grouped by
     languages and the catalogs for all programs are kept in the same
     place.

     To tell the ‘catopen’ function where the catalog for the program
     can be found the user can set the environment variable ‘NLSPATH’ to
     a value which describes her/his choice.  Since this value must be
     usable for different languages and locales it cannot be a simple
     string.  Instead it is a format string (similar to ‘printf’’s).  An
     example is

          /usr/share/locale/%L/%N:/usr/share/locale/%L/LC_MESSAGES/%N

     First one can see that more than one directory can be specified
     (with the usual syntax of separating them by colons).  The next
     things to observe are the format string, ‘%L’ and ‘%N’ in this
     case.  The ‘catopen’ function knows about several of them and the
     replacement for all of them is of course different.

     ‘%N’
          This format element is substituted with the name of the
          catalog file.  This is the value of the CAT_NAME argument
          given to ‘catgets’.

     ‘%L’
          This format element is substituted with the name of the
          currently selected locale for translating messages.  How this
          is determined is explained below.

     ‘%l’
          (This is the lowercase ell.)  This format element is
          substituted with the language element of the locale name.  The
          string describing the selected locale is expected to have the
          form ‘LANG[_TERR[.CODESET]]’ and this format uses the first
          part LANG.

     ‘%t’
          This format element is substituted by the territory part TERR
          of the name of the currently selected locale.  See the
          explanation of the format above.

     ‘%c’
          This format element is substituted by the codeset part CODESET
          of the name of the currently selected locale.  See the
          explanation of the format above.

     ‘%%’
          Since ‘%’ is used as a meta character there must be a way to
          express the ‘%’ character in the result itself.  Using ‘%%’
          does this just like it works for ‘printf’.

     Using ‘NLSPATH’ allows arbitrary directories to be searched for
     message catalogs while still allowing different languages to be
     used.  If the ‘NLSPATH’ environment variable is not set, the
     default value is

          PREFIX/share/locale/%L/%N:PREFIX/share/locale/%L/LC_MESSAGES/%N

     where PREFIX is given to ‘configure’ while installing the GNU C
     Library (this value is in many cases ‘/usr’ or the empty string).

     The remaining problem is to decide which must be used.  The value
     decides about the substitution of the format elements mentioned
     above.  First of all the user can specify a path in the message
     catalog name (i.e., the name contains a slash character).  In this
     situation the ‘NLSPATH’ environment variable is not used.  The
     catalog must exist as specified in the program, perhaps relative to
     the current working directory.  This situation in not desirable and
     catalogs names never should be written this way.  Beside this, this
     behavior is not portable to all other platforms providing the
     ‘catgets’ interface.

     Otherwise the values of environment variables from the standard
     environment are examined (*note Standard Environment::).  Which
     variables are examined is decided by the FLAG parameter of
     ‘catopen’.  If the value is ‘NL_CAT_LOCALE’ (which is defined in
     ‘nl_types.h’) then the ‘catopen’ function uses the name of the
     locale currently selected for the ‘LC_MESSAGES’ category.

     If FLAG is zero the ‘LANG’ environment variable is examined.  This
     is a left-over from the early days when the concept of locales had
     not even reached the level of POSIX locales.

     The environment variable and the locale name should have a value of
     the form ‘LANG[_TERR[.CODESET]]’ as explained above.  If no
     environment variable is set the ‘"C"’ locale is used which prevents
     any translation.

     The return value of the function is in any case a valid string.
     Either it is a translation from a message catalog or it is the same
     as the STRING parameter.  So a piece of code to decide whether a
     translation actually happened must look like this:

          {
            char *trans = catgets (desc, set, msg, input_string);
            if (trans == input_string)
              {
                /* Something went wrong.  */
              }
          }

     When an error occurs the global variable ‘errno’ is set to

     EBADF
          The catalog does not exist.
     ENOMSG
          The set/message tuple does not name an existing element in the
          message catalog.

     While it sometimes can be useful to test for errors programs
     normally will avoid any test.  If the translation is not available
     it is no big problem if the original, untranslated message is
     printed.  Either the user understands this as well or s/he will
     look for the reason why the messages are not translated.

   Please note that the currently selected locale does not depend on a
call to the ‘setlocale’ function.  It is not necessary that the locale
data files for this locale exist and calling ‘setlocale’ succeeds.  The
‘catopen’ function directly reads the values of the environment
variables.

 -- Function: char * catgets (nl_catd CATALOG_DESC, int SET, int
          MESSAGE, const char *STRING)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The function ‘catgets’ has to be used to access the message catalog
     previously opened using the ‘catopen’ function.  The CATALOG_DESC
     parameter must be a value previously returned by ‘catopen’.

     The next two parameters, SET and MESSAGE, reflect the internal
     organization of the message catalog files.  This will be explained
     in detail below.  For now it is interesting to know that a catalog
     can consist of several sets and the messages in each thread are
     individually numbered using numbers.  Neither the set number nor
     the message number must be consecutive.  They can be arbitrarily
     chosen.  But each message (unless equal to another one) must have
     its own unique pair of set and message numbers.

     Since it is not guaranteed that the message catalog for the
     language selected by the user exists the last parameter STRING
     helps to handle this case gracefully.  If no matching string can be
     found STRING is returned.  This means for the programmer that

        • the STRING parameters should contain reasonable text (this
          also helps to understand the program seems otherwise there
          would be no hint on the string which is expected to be
          returned.
        • all STRING arguments should be written in the same language.

   It is somewhat uncomfortable to write a program using the ‘catgets’
functions if no supporting functionality is available.  Since each
set/message number tuple must be unique the programmer must keep lists
of the messages at the same time the code is written.  And the work
between several people working on the same project must be coordinated.
We will see how some of these problems can be relaxed a bit (*note
Common Usage::).

 -- Function: int catclose (nl_catd CATALOG_DESC)
     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe corrupt mem |
     *Note POSIX Safety Concepts::.

     The ‘catclose’ function can be used to free the resources
     associated with a message catalog which previously was opened by a
     call to ‘catopen’.  If the resources can be successfully freed the
     function returns ‘0’.  Otherwise it returns ‘−1’ and the global
     variable ‘errno’ is set.  Errors can occur if the catalog
     descriptor CATALOG_DESC is not valid in which case ‘errno’ is set
     to ‘EBADF’.