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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