PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

C99(1P)                   POSIX Programmer's Manual                  C99(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       c99 — compile standard C programs

SYNOPSIS         top

       c99 [options...] pathname [[pathname] [−I directory]
           [−L directory] [−l library]]...

DESCRIPTION         top

       The c99 utility is an interface to the standard C compilation system;
       it shall accept source code conforming to the ISO C standard. The
       system conceptually consists of a compiler and link editor. The input
       files referenced by pathname operands and −l option-arguments shall
       be compiled and linked to produce an executable file. (It is
       unspecified whether the linking occurs entirely within the operation
       of c99; some implementations may produce objects that are not fully
       resolved until the file is executed.)

       If the −c option is specified, for all pathname operands of the form
       file.c, the files:

           $(basename pathname .c).o

       shall be created as the result of successful compilation. If the −c
       option is not specified, it is unspecified whether such .o files are
       created or deleted for the file.c operands.

       If there are no options that prevent link editing (such as −c or −E),
       and all input files compile and link without error, the resulting
       executable file shall be written according to the −o outfile option
       (if present) or to the file a.out.

       The executable file shall be created as specified in Section 1.1.1.4,
       File Read, Write, and Creation, except that the file permission bits
       shall be set to: S_IRWXO | S_IRWXG | S_IRWXU

       and the bits specified by the umask of the process shall be cleared.

OPTIONS         top

       The c99 utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except that:

        *  Options can be interspersed with operands.

        *  The order of specifying the −L and −l options, and the order of
           specifying −l options with respect to pathname operands is
           significant.

        *  Conforming applications shall specify each option separately;
           that is, grouping option letters (for example, −cO) need not be
           recognized by all implementations.

       The following options shall be supported:

       −c        Suppress the link-edit phase of the compilation, and do not
                 remove any object files that are produced.

       −D name[=value]
                 Define name as if by a C-language #define directive. If no
                 =value is given, a value of 1 shall be used. The −D option
                 has lower precedence than the −U option. That is, if name
                 is used in both a −U and a −D option, name shall be
                 undefined regardless of the order of the options.
                 Additional implementation-defined names may be provided by
                 the compiler. Implementations shall support at least 2048
                 bytes of −D definitions and 256 names.

       −E        Copy C-language source files to standard output, expanding
                 all preprocessor directives; no compilation shall be
                 performed. If any operand is not a text file, the effects
                 are unspecified.

       −g        Produce symbolic information in the object or executable
                 files; the nature of this information is unspecified, and
                 may be modified by implementation-defined interactions with
                 other options.

       −I directory
                 Change the algorithm for searching for headers whose names
                 are not absolute pathnames to look in the directory named
                 by the directory pathname before looking in the usual
                 places. Thus, headers whose names are enclosed in double-
                 quotes ("") shall be searched for first in the directory of
                 the file with the #include line, then in directories named
                 in −I options, and last in the usual places. For headers
                 whose names are enclosed in angle brackets ("<>"), the
                 header shall be searched for only in directories named in
                 −I options and then in the usual places. Directories named
                 in −I options shall be searched in the order specified. If
                 the −I option is used to specify a directory that is one of
                 the usual places searched by default, the results are
                 unspecified. Implementations shall support at least ten
                 instances of this option in a single c99 command
                 invocation.

       −L directory
                 Change the algorithm of searching for the libraries named
                 in the −l objects to look in the directory named by the
                 directory pathname before looking in the usual places.
                 Directories named in −L options shall be searched in the
                 order specified. If the −L option is used to specify a
                 directory that is one of the usual places searched by
                 default, the results are unspecified. Implementations shall
                 support at least ten instances of this option in a single
                 c99 command invocation. If a directory specified by a −L
                 option contains files with names starting with any of the
                 strings "libc.", "libl.", "libpthread.", "libm.", "librt.",
                 "libtrace.", "libxnet.", or "liby.", the results are
                 unspecified.

       −l library
                 Search the library named liblibrary.a.  A library shall be
                 searched when its name is encountered, so the placement of
                 a −l option is significant. Several standard libraries can
                 be specified in this manner, as described in the EXTENDED
                 DESCRIPTION section. Implementations may recognize
                 implementation-defined suffixes other than .a as denoting
                 libraries.

       −O optlevel
                 Specify the level of code optimization. If the optlevel
                 option-argument is the digit '0', all special code
                 optimizations shall be disabled. If it is the digit '1',
                 the nature of the optimization is unspecified. If the −O
                 option is omitted, the nature of the system's default
                 optimization is unspecified. It is unspecified whether code
                 generated in the presence of the −O 0 option is the same as
                 that generated when −O is omitted. Other optlevel values
                 may be supported.

       −o outfile
                 Use the pathname outfile, instead of the default a.out, for
                 the executable file produced. If the −o option is present
                 with −c or −E, the result is unspecified.

       −s        Produce object or executable files, or both, from which
                 symbolic and other information not required for proper
                 execution using the exec family defined in the System
                 Interfaces volume of POSIX.1‐2008 has been removed
                 (stripped). If both −g and −s options are present, the
                 action taken is unspecified.

       −U name   Remove any initial definition of name.

       Multiple instances of the −D, −I, −L, −l, and −U options can be
       specified.

OPERANDS         top

       The application shall ensure that at least one pathname operand is
       specified. The following forms for pathname operands shall be
       supported:

       file.c    A C-language source file to be compiled and optionally
                 linked. The application shall ensure that the operand is of
                 this form if the −c option is used.

       file.a    A library of object files typically produced by the ar
                 utility, and passed directly to the link editor.
                 Implementations may recognize implementation-defined
                 suffixes other than .a as denoting object file libraries.

       file.o    An object file produced by c99 −c and passed directly to
                 the link editor. Implementations may recognize
                 implementation-defined suffixes other than .o as denoting
                 object files.

       The processing of other files is implementation-defined.

STDIN         top

       Not used.

INPUT FILES         top

       Each input file shall be one of the following: a text file containing
       a C-language source program, an object file in the format produced by
       c99 −c, or a library of object files, in the format produced by
       archiving zero or more object files, using ar.  Implementations may
       supply additional utilities that produce files in these formats.
       Additional input file formats are implementation-defined.

ENVIRONMENT VARIABLES         top

       The following environment variables shall affect the execution of
       c99:

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1‐2008, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale
                 categories.)

       LC_ALL    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       LC_CTYPE  Determine the locale for the interpretation of sequences of
                 bytes of text data as characters (for example, single-byte
                 as opposed to multi-byte characters in arguments and input
                 files).

       LC_MESSAGES
                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written to
                 standard error.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.

       TMPDIR    Provide a pathname that should override the default
                 directory for temporary files, if any.  On XSI-conforming
                 systems, provide a pathname that shall override the default
                 directory for temporary files, if any.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       If more than one pathname operand ending in .c (or possibly other
       unspecified suffixes) is given, for each such file:

           "%s:\n", <pathname>

       may be written. These messages, if written, shall precede the
       processing of each input file; they shall not be written to the
       standard output if they are written to the standard error, as
       described in the STDERR section.

       If the −E option is specified, the standard output shall be a text
       file that represents the results of the preprocessing stage of the
       language; it may contain extra information appropriate for subsequent
       compilation passes.

STDERR         top

       The standard error shall be used only for diagnostic messages.  If
       more than one pathname operand ending in .c (or possibly other
       unspecified suffixes) is given, for each such file:

           "%s:\n", <pathname>

       may be written to allow identification of the diagnostic and warning
       messages with the appropriate input file. These messages, if written,
       shall precede the processing of each input file; they shall not be
       written to the standard error if they are written to the standard
       output, as described in the STDOUT section.

       This utility may produce warning messages about certain conditions
       that do not warrant returning an error (non-zero) exit value.

OUTPUT FILES         top

       Object files or executable files or both are produced in unspecified
       formats. If the pathname of an object file or executable file to be
       created by c99 resolves to an existing directory entry for a file
       that is not a regular file, it is unspecified whether c99 shall
       attempt to create the file or shall issue a diagnostic and exit with
       a non-zero exit status.

EXTENDED DESCRIPTION         top

   Standard Libraries
       The c99 utility shall recognize the following −l options for standard
       libraries:

       −l c      This option shall make available all interfaces referenced
                 in the System Interfaces volume of POSIX.1‐2008, with the
                 possible exception of those interfaces listed as residing
                 in <aio.h>, <arpa/inet.h>, <complex.h>, <fenv.h>, <math.h>,
                 <mqueue.h>, <netdb.h>, <net/if.h>, <netinet/in.h>,
                 <pthread.h>, <sched.h>, <semaphore.h>, <spawn.h>,
                 <sys/socket.h>, pthread_kill(), and pthread_sigmask() in
                 <signal.h>, <trace.h>, interfaces marked as optional in
                 <sys/mman.h>, interfaces marked as ADV (Advisory
                 Information) in <fcntl.h>, and interfaces beginning with
                 the prefix clock_ or time_ in <time.h>.  This option shall
                 not be required to be present to cause a search of this
                 library.

       −l l      This option shall make available all interfaces required by
                 the C-language output of lex that are not made available
                 through the −l c option.

       −l pthread
                 This option shall make available all interfaces referenced
                 in <pthread.h> and pthread_kill() and pthread_sigmask()
                 referenced in <signal.h>.  An implementation may search
                 this library in the absence of this option.

       −l m      This option shall make available all interfaces referenced
                 in <math.h>, <complex.h>, and <fenv.h>.  An implementation
                 may search this library in the absence of this option.

       −l rt     This option shall make available all interfaces referenced
                 in <aio.h>, <mqueue.h>, <sched.h>, <semaphore.h>, and
                 <spawn.h>, interfaces marked as optional in <sys/mman.h>,
                 interfaces marked as ADV (Advisory Information) in
                 <fcntl.h>, and interfaces beginning with the prefix clock_
                 and time_ in <time.h>.  An implementation may search this
                 library in the absence of this option.

       −l trace  This option shall make available all interfaces referenced
                 in <trace.h>.  An implementation may search this library in
                 the absence of this option.

       −l xnet   This option shall make available all interfaces referenced
                 in <arpa/inet.h>, <netdb.h>, <net/if.h>, <netinet/in.h>,
                 and <sys/socket.h>.  An implementation may search this
                 library in the absence of this option.

       −l y      This option shall make available all interfaces required by
                 the C-language output of yacc that are not made available
                 through the −l c option.

       In the absence of options that inhibit invocation of the link editor,
       such as −c or −E, the c99 utility shall cause the equivalent of a
       −l c option to be passed to the link editor after the last pathname
       operand or −l option, causing it to be searched after all other
       object files and libraries are loaded.

       It is unspecified whether the libraries libc.a, libl.a, libm.a,
       libpthread.a, librt.a, libtrace.a, libxnet.a, or liby.a exist as
       regular files. The implementation may accept as −l option-arguments
       names of objects that do not exist as regular files.

   External Symbols
       The C compiler and link editor shall support the significance of
       external symbols up to a length of at least 31 bytes; the action
       taken upon encountering symbols exceeding the implementation-defined
       maximum symbol length is unspecified.

       The compiler and link editor shall support a minimum of 511 external
       symbols per source or object file, and a minimum of 4095 external
       symbols in total. A diagnostic message shall be written to the
       standard output if the implementation-defined limit is exceeded;
       other actions are unspecified.

   Header Search
       If a file with the same name as one of the standard headers defined
       in the Base Definitions volume of POSIX.1‐2008, Chapter 13, Headers,
       not provided as part of the implementation, is placed in any of the
       usual places that are searched by default for headers, the results
       are unspecified.

   Programming Environments
       All implementations shall support one of the following programming
       environments as a default. Implementations may support more than one
       of the following programming environments. Applications can use
       sysconf() or getconf to determine which programming environments are
       supported.

                  Table 4-4: Programming Environments: Type Sizes

         ┌────────────────────────┬─────────┬─────────┬─────────┬─────────┐
         │Programming Environment Bits in Bits in Bits in Bits in │
         │     getconf Name       int   long   pointer off_t  │
         ├────────────────────────┼─────────┼─────────┼─────────┼─────────┤
         │_POSIX_V7_ILP32_OFF32   │    32   │    32   │    32   │    32   │
         │_POSIX_V7_ILP32_OFFBIG  │    32   │    32   │    32   │   ≥64   │
         │_POSIX_V7_LP64_OFF64    │    32   │    64   │    64   │    64   │
         │_POSIX_V7_LPBIG_OFFBIG  │   ≥32   │   ≥64   │   ≥64   │   ≥64   │
         └────────────────────────┴─────────┴─────────┴─────────┴─────────┘
       All implementations shall support one or more environments where the
       widths of the following types are no greater than the width of type
       long:

                        blksize_t   ptrdiff_t     tcflag_t
                        cc_t        size_t        wchar_t
                        mode_t      speed_t       wint_t
                        nfds_t      ssize_t
                        pid_t       suseconds_t

       The executable files created when these environments are selected
       shall be in a proper format for execution by the exec family of
       functions. Each environment may be one of the ones in Table 4-4,
       Programming Environments: Type Sizes, or it may be another
       environment. The names for the environments that meet this
       requirement shall be output by a getconf command using the
       POSIX_V7_WIDTH_RESTRICTED_ENVS argument, as a <newline>-separated
       list of names suitable for use with the getconf −v option. If more
       than one environment meets the requirement, the names of all such
       environments shall be output on separate lines. Any of these names
       can then be used in a subsequent getconf command to obtain the flags
       specific to that environment with the following suffixes added as
       appropriate:

       _CFLAGS   To get the C compiler flags.

       _LDFLAGS  To get the linker/loader flags.

       _LIBS     To get the libraries.

       This requirement may be removed in a future version.

       When this utility processes a file containing a function called
       main(), it shall be defined with a return type equivalent to int.
       Using return from the initial call to main() shall be equivalent
       (other than with respect to language scope issues) to calling exit()
       with the returned value. Reaching the end of the initial call to
       main() shall be equivalent to calling exit(0).  The implementation
       shall not declare a prototype for this function.

       Implementations provide configuration strings for C compiler flags,
       linker/loader flags, and libraries for each supported environment.
       When an application needs to use a specific programming environment
       rather than the implementation default programming environment while
       compiling, the application shall first verify that the implementation
       supports the desired environment. If the desired programming
       environment is supported, the application shall then invoke c99 with
       the appropriate C compiler flags as the first options for the
       compile, the appropriate linker/loader flags after any other options
       except −l but before any operands or −l options, and the appropriate
       libraries at the end of the operands and −l options.

       Conforming applications shall not attempt to link together object
       files compiled for different programming models. Applications shall
       also be aware that binary data placed in shared memory or in files
       might not be recognized by applications built for other programming
       models.

                Table 4-5: Programming Environments: c99 Arguments

  ┌────────────────────────┬─────────────────────┬───────────────────────────────┐
  │Programming Environment │                     │         c99 Arguments         │
  │     getconf Name       Use         getconf Name          │
  ├────────────────────────┼─────────────────────┼───────────────────────────────┤
  │_POSIX_V7_ILP32_OFF32   │ C Compiler Flags    │ POSIX_V7_ILP32_OFF32_CFLAGS   │
  │                        │ Linker/Loader Flags │ POSIX_V7_ILP32_OFF32_LDFLAGS  │
  │                        │ Libraries           │ POSIX_V7_ILP32_OFF32_LIBS     │
  ├────────────────────────┼─────────────────────┼───────────────────────────────┤
  │_POSIX_V7_ILP32_OFFBIG  │ C Compiler Flags    │ POSIX_V7_ILP32_OFFBIG_CFLAGS  │
  │                        │ Linker/Loader Flags │ POSIX_V7_ILP32_OFFBIG_LDFLAGS │
  │                        │ Libraries           │ POSIX_V7_ILP32_OFFBIG_LIBS    │
  ├────────────────────────┼─────────────────────┼───────────────────────────────┤
  │_POSIX_V7_LP64_OFF64    │ C Compiler Flags    │ POSIX_V7_LP64_OFF64_CFLAGS    │
  │                        │ Linker/Loader Flags │ POSIX_V7_LP64_OFF64_LDFLAGS   │
  │                        │ Libraries           │ POSIX_V7_LP64_OFF64_LIBS      │
  ├────────────────────────┼─────────────────────┼───────────────────────────────┤
  │_POSIX_V7_LPBIG_OFFBIG  │ C Compiler Flags    │ POSIX_V7_LPBIG_OFFBIG_CFLAGS  │
  │                        │ Linker/Loader Flags │ POSIX_V7_LPBIG_OFFBIG_LDFLAGS │
  │                        │ Libraries           │ POSIX_V7_LPBIG_OFFBIG_LIBS    │
  └────────────────────────┴─────────────────────┴───────────────────────────────┘
       In addition to the type size programming environments above, all
       implementations also support a multi-threaded programming environment
       that is orthogonal to all of the programming environments listed
       above.  The getconf utility can be used to get flags for the threaded
       programming environment, as indicated in Table 4-6, Threaded
       Programming Environment: c99 Arguments.

            Table 4-6: Threaded Programming Environment: c99 Arguments

     ┌────────────────────────┬─────────────────────┬──────────────────────────┐
     │Programming Environment │                     │      c99 Arguments       │
     │     getconf Name       Use         getconf Name       │
     ├────────────────────────┼─────────────────────┼──────────────────────────┤
     │_POSIX_THREADS          │ C Compiler Flags    │ POSIX_V7_THREADS_CFLAGS  │
     │                        │ Linker/Loader Flags │ POSIX_V7_THREADS_LDFLAGS │
     └────────────────────────┴─────────────────────┴──────────────────────────┘
       These programming environment flags may be used in conjunction with
       any of the type size programming environments supported by the
       implementation.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful compilation or link edit.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       When c99 encounters a compilation error that causes an object file
       not to be created, it shall write a diagnostic to standard error and
       continue to compile other source code operands, but it shall not
       perform the link phase and return a non-zero exit status. If the link
       edit is unsuccessful, a diagnostic message shall be written to
       standard error and c99 exits with a non-zero status. A conforming
       application shall rely on the exit status of c99, rather than on the
       existence or mode of the executable file.

       The following sections are informative.

APPLICATION USAGE         top

       Since the c99 utility usually creates files in the current directory
       during the compilation process, it is typically necessary to run the
       c99 utility in a directory in which a file can be created.

       On systems providing POSIX Conformance (see the Base Definitions
       volume of POSIX.1‐2008, Chapter 2, Conformance), c99 is required only
       with the C-Language Development option; XSI-conformant systems always
       provide c99.

       Some historical implementations have created .o files when −c is not
       specified and more than one source file is given. Since this area is
       left unspecified, the application cannot rely on .o files being
       created, but it also must be prepared for any related .o files that
       already exist being deleted at the completion of the link edit.

       There is the possible implication that if a user supplies versions of
       the standard functions (before they would be encountered by an
       implicit −l c or explicit −l m), that those versions would be used in
       place of the standard versions.  There are various reasons this might
       not be true (functions defined as macros, manipulations for clean
       name space, and so on), so the existence of files named in the same
       manner as the standard libraries within the −L directories is
       explicitly stated to produce unspecified behavior.

       All of the functions specified in the System Interfaces volume of
       POSIX.1‐2008 may be made visible by implementations when the Standard
       C Library is searched. Conforming applications must explicitly
       request searching the other standard libraries when functions made
       visible by those libraries are used.

       In the ISO C standard the mapping from physical source characters to
       the C source character set is implementation-defined. Implementations
       may strip white-space characters before the terminating <newline> of
       a (physical) line as part of this mapping and, as a consequence of
       this, one or more white-space characters (and no other characters)
       between a <backslash> character and the <newline> character that
       terminates the line produces implementation-defined results. Portable
       applications should not use such constructs.

       Some c99 compilers not conforming to POSIX.1‐2008 do not support
       trigraphs by default.

EXAMPLES         top

        1. The following usage example compiles foo.c and creates the
           executable file foo:

               c99 −o foo foo.c

           The following usage example compiles foo.c and creates the object
           file foo.o:

               c99 −c foo.c

           The following usage example compiles foo.c and creates the
           executable file a.out:

               c99 foo.c

           The following usage example compiles foo.c, links it with bar.o,
           and creates the executable file a.out.  It may also create and
           leave foo.o:

               c99 foo.c bar.o

        2. The following example shows how an application using threads
           interfaces can test for support of and use a programming
           environment supporting 32-bit int, long, and pointer types and an
           off_t type using at least 64 bits:

               offbig_env=$(getconf _POSIX_V7_ILP32_OFFBIG)
               if [ $offbig_env != "-1" ] && [ $offbig_env != "undefined" ]
               then
                   c99 $(getconf POSIX_V7_ILP32_OFFBIG_CFLAGS) \
                   $(getconf POSIX_V7_THREADS_CFLAGS) -D_XOPEN_SOURCE=700 \
                   $(getconf POSIX_V7_ILP32_OFFBIG_LDFLAGS) \
                   $(getconf POSIX_V7_THREADS_LDFLAGS) foo.c -o foo \
                   $(getconf POSIX_V7_ILP32_OFFBIG_LIBS) \
                   -l pthread
               else
                   echo ILP32_OFFBIG programming environment not supported
                   exit 1
               fi

        3. The following examples clarify the use and interactions of −L and
           −l options.

           Consider the case in which module a.c calls function f() in
           library libQ.a, and module b.c calls function g() in library
           libp.a.  Assume that both libraries reside in /a/b/c.  The
           command line to compile and link in the desired way is:

               c99 −L /a/b/c main.o a.c −l Q b.c −l p

           In this case the −L option need only precede the first −l option,
           since both libQ.a and libp.a reside in the same directory.

           Multiple −L options can be used when library name collisions
           occur. Building on the previous example, suppose that the user
           wants to use a new libp.a, in /a/a/a, but still wants f() from
           /a/b/c/libQ.a:

               c99 −L /a/a/a −L /a/b/c main.o a.c −l Q b.c −l p

           In this example, the linker searches the −L options in the order
           specified, and finds /a/a/a/libp.a before /a/b/c/libp.a when
           resolving references for b.c.  The order of the −l options is
           still important, however.

        4. The following example shows how an application can use a
           programming environment where the widths of the following types:
           blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t,
           speed_t, ssize_t, suseconds_t, tcflag_t, wchar_t, wint_t

           are no greater than the width of type long:

               # First choose one of the listed environments ...

               # ... if there are no additional constraints, the first one will do:
               CENV=$(getconf POSIX_V7_WIDTH_RESTRICTED_ENVS | head -n l)

               # ... or, if an environment that supports large files is preferred,
               # look for names that contain "OFF64" or "OFFBIG". (This chooses
               # the last one in the list if none match.)
               for CENV in $(getconf POSIX_V7_WIDTH_RESTRICTED_ENVS)
               do
                   case $CENV in
                   *OFF64*|*OFFBIG*) break ;;
                   esac
               done

               # The chosen environment name can now be used like this:

               c99 $(getconf ${CENV}_CFLAGS) -D _POSIX_C_SOURCE=200809L \
               $(getconf ${CENV}_LDFLAGS) foo.c -o foo \
               $(getconf ${CENV}_LIBS)

RATIONALE         top

       The c99 utility is based on the c89 utility originally introduced in
       the ISO POSIX‐2:1993 standard.

       Some of the changes from c89 include the ability to intersperse
       options and operands (which many c89 implementations allowed despite
       it not being specified), the description of −l as an option instead
       of an operand, and the modification to the contents of the Standard
       Libraries section to account for new headers and options; for
       example, <spawn.h> added to the description of −l rt, and −l trace
       added for the Tracing option.

       POSIX.1‐2008 specifies that the c99 utility must be able to use
       regular files for *.o files and for a.out files. Implementations are
       free to overwrite existing files of other types when attempting to
       create object files and executable files, but are not required to do
       so. If something other than a regular file is specified and using it
       fails for any reason, c99 is required to issue a diagnostic message
       and exit with a non-zero exit status. But for some file types, the
       problem may not be noticed for a long time. For example, if a FIFO
       named a.out exists in the current directory, c99 may attempt to open
       a.out and will hang in the open() call until another process opens
       the FIFO for reading. Then c99 may write most of the a.out to the
       FIFO and fail when it tries to seek back close to the start of the
       file to insert a timestamp (FIFOs are not seekable files). The c99
       utility is also allowed to issue a diagnostic immediately if it
       encounters an a.out or *.o file that is not a regular file. For
       portable use, applications should ensure that any a.out, −o option-
       argument, or *.o files corresponding to any *.c files do not conflict
       with names already in use that are not regular files or symbolic
       links that point to regular files.

       On many systems, multi-threaded applications run in a programming
       environment that is distinct from that used by single-threaded
       applications. This multi-threaded programming environment (in
       addition to needing to specify −l pthread at link time) may require
       additional flags to be set when headers are processed at compile time
       (−D_REENTRANT being common). This programming environment is
       orthogonal to the type size programming environments discussed above
       and listed in Table 4-4, Programming Environments: Type Sizes.  This
       version of the standard adds getconf utility calls to provide the C
       compiler flags and linker/loader flags needed to support multi-
       threaded applications. Note that on a system where single-threaded
       applications are a special case of a multi-threaded application, both
       of these getconf calls may return NULL strings; on other
       implementations both of these strings may be non-NULL strings.

       The C standardization committee invented trigraphs (e.g., "??!" to
       represent '|') to address character portability problems in
       development environments based on national variants of the 7-bit
       ISO/IEC 646:1991 standard character set. However, these environments
       were already obsolete by the time the first ISO C standard was
       published, and in practice trigraphs have not been used for their
       intended purpose, and usually are intended to have their original
       meaning in K&R C.  For example, in practice a C-language source
       string like "What??!" is usually intended to end in two <question-
       mark> characters and an <exclamation-mark>, not in '|'.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 1.1.1.4, File Read, Write, and Creation, ar(1p), getconf(1p),
       make(1p), nm(1p), strip(1p), umask(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines, Chapter 13,
       Headers

       The System Interfaces volume of POSIX.1‐2008, exec(1p), sysconf(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                             C99(1P)