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(autoconf.info)Particular Headers


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Particular Header Checks
------------------------

   These macros check for particular system header files--whether they
exist, and in some cases whether they declare certain symbols.

 - Macro: AC_DECL_SYS_SIGLIST
     Define `SYS_SIGLIST_DECLARED' if the variable `sys_siglist' is
     declared in a system header file, either `signal.h' or `unistd.h'.

 - Macro: AC_DIR_HEADER
     Like calling `AC_HEADER_DIRENT' and `AC_FUNC_CLOSEDIR_VOID', but
     defines a different set of C preprocessor macros to indicate which
     header file is found.  This macro and the names it defines are
     considered obsolete.  The names it defines are:

    `dirent.h'
          `DIRENT'

    `sys/ndir.h'
          `SYSNDIR'

    `sys/dir.h'
          `SYSDIR'

    `ndir.h'
          `NDIR'

     In addition, if the `closedir' function does not return a
     meaningful value, define `VOID_CLOSEDIR'.

 - Macro: AC_HEADER_DIRENT
     Check for the following header files, and for the first one that is
     found and defines `DIR', define the listed C preprocessor macro:

    `dirent.h'
          `HAVE_DIRENT_H'

    `sys/ndir.h'
          `HAVE_SYS_NDIR_H'

    `sys/dir.h'
          `HAVE_SYS_DIR_H'

    `ndir.h'
          `HAVE_NDIR_H'

     The directory library declarations in the source code should look
     something like the following:

          #if HAVE_DIRENT_H
          # include <dirent.h>
          # define NAMLEN(dirent) strlen((dirent)->d_name)
          #else
          # define dirent direct
          # define NAMLEN(dirent) (dirent)->d_namlen
          # if HAVE_SYS_NDIR_H
          #  include <sys/ndir.h>
          # endif
          # if HAVE_SYS_DIR_H
          #  include <sys/dir.h>
          # endif
          # if HAVE_NDIR_H
          #  include <ndir.h>
          # endif
          #endif

     Using the above declarations, the program would declare variables
     to be type `struct dirent', not `struct direct', and would access
     the length of a directory entry name by passing a pointer to a
     `struct dirent' to the `NAMLEN' macro.

     This macro also checks for the SCO Xenix `dir' and `x' libraries.

 - Macro: AC_HEADER_MAJOR
     If `sys/types.h' does not define `major', `minor', and `makedev',
     but `sys/mkdev.h' does, define `MAJOR_IN_MKDEV'; otherwise, if
     `sys/sysmacros.h' does, define `MAJOR_IN_SYSMACROS'.

 - Macro: AC_HEADER_STDC
     Define `STDC_HEADERS' if the system has ANSI C header files.
     Specifically, this macro checks for `stdlib.h', `stdarg.h',
     `string.h', and `float.h'; if the system has those, it probably
     has the rest of the ANSI C header files.  This macro also checks
     whether `string.h' declares `memchr' (and thus presumably the
     other `mem' functions), whether `stdlib.h' declare `free' (and
     thus presumably `malloc' and other related functions), and whether
     the `ctype.h' macros work on characters with the high bit set, as
     ANSI C requires.

     Use `STDC_HEADERS' instead of `__STDC__' to determine whether the
     system has ANSI-compliant header files (and probably C library
     functions) because many systems that have GCC do not have ANSI C
     header files.

     On systems without ANSI C headers, there is so much variation that
     it is probably easier to declare the functions you use than to
     figure out exactly what the system header files declare.  Some
     systems contain a mix of functions ANSI and BSD; some are mostly
     ANSI but lack `memmove'; some define the BSD functions as macros in
     `string.h' or `strings.h'; some have only the BSD functions but
     `string.h'; some declare the memory functions in `memory.h', some
     in `string.h'; etc.  It is probably sufficient to check for one
     string function and one memory function; if the library has the
     ANSI versions of those then it probably has most of the others.
     If you put the following in `configure.in':

          AC_HEADER_STDC
          AC_CHECK_FUNCS(strchr memcpy)

     then, in your code, you can put declarations like this:

          #if STDC_HEADERS
          # include <string.h>
          #else
          # ifndef HAVE_STRCHR
          #  define strchr index
          #  define strrchr rindex
          # endif
          char *strchr (), *strrchr ();
          # ifndef HAVE_MEMCPY
          #  define memcpy(d, s, n) bcopy ((s), (d), (n))
          #  define memmove(d, s, n) bcopy ((s), (d), (n))
          # endif
          #endif

     If you use a function like `memchr', `memset', `strtok', or
     `strspn', which have no BSD equivalent, then macros won't suffice;
     you must provide an implementation of each function.  An easy way
     to incorporate your implementations only when needed (since the
     ones in system C libraries may be hand optimized) is to, taking
     `memchr' for example, put it in `memchr.c' and use
     `AC_REPLACE_FUNCS(memchr)'.

 - Macro: AC_HEADER_SYS_WAIT
     If `sys/wait.h' exists and is compatible with POSIX.1, define
     `HAVE_SYS_WAIT_H'.  Incompatibility can occur if `sys/wait.h' does
     not exist, or if it uses the old BSD `union wait' instead of `int'
     to store a status value.  If `sys/wait.h' is not POSIX.1
     compatible, then instead of including it, define the POSIX.1
     macros with their usual interpretations.  Here is an example:

          #include <sys/types.h>
          #if HAVE_SYS_WAIT_H
          # include <sys/wait.h>
          #endif
          #ifndef WEXITSTATUS
          # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8)
          #endif
          #ifndef WIFEXITED
          # define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
          #endif

 - Macro: AC_MEMORY_H
     Define `NEED_MEMORY_H' if `memcpy', `memcmp', etc. are not
     declared in `string.h' and `memory.h' exists.  This macro is
     obsolete; instead, use `AC_CHECK_HEADERS(memory.h)'.  See the
     example for `AC_HEADER_STDC'.

 - Macro: AC_UNISTD_H
     Define `HAVE_UNISTD_H' if the system has `unistd.h'.  This macro
     is obsolete; instead, use `AC_CHECK_HEADERS(unistd.h)'.

     The way to check if the system supports POSIX.1 is:

          #if HAVE_UNISTD_H
          # include <sys/types.h>
          # include <unistd.h>
          #endif
          
          #ifdef _POSIX_VERSION
          /* Code for POSIX.1 systems.  */
          #endif

     `_POSIX_VERSION' is defined when `unistd.h' is included on POSIX.1
     systems.  If there is no `unistd.h', it is definitely not a
     POSIX.1 system.  However, some non-POSIX.1 systems do have
     `unistd.h'.

 - Macro: AC_USG
     Define `USG' if the system does not have `strings.h', `rindex',
     `bzero', etc.  This implies that it has `string.h', `strrchr',
     `memset', etc.

     The symbol `USG' is obsolete.  Instead of this macro, see the
     example for `AC_HEADER_STDC'.


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