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5.6.2 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_HEADER_DIRENT
Check for the following header files. 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 your 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 of 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_STAT
If the macros S_ISDIR, S_ISREG, etc. defined in `sys/stat.h' do not work properly (returning false positives), define STAT_MACROS_BROKEN. This is the case on Tektronix UTekV, Amdahl UTS and Motorola System V/88.

Macro: AC_HEADER_STDBOOL
If `stdbool.h' exists and is conformant to C99, define HAVE_STDBOOL_H to 1; if the type _Bool is defined, define HAVE__BOOL to 1. To fulfill the C99 requirements, your `system.h' should contain the following code:

@verbatim #if HAVE_STDBOOL_H # include <stdbool.h> #else # if ! HAVE__BOOL # ifdef __cplusplus typedef bool _Bool; # else typedef unsigned char _Bool; # endif # endif # define bool _Bool # define false 0 # define true 1 # define __bool_true_false_are_defined 1 #endif

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 from 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.ac':

 
AC_HEADER_STDC
AC_CHECK_FUNCS(strchr memcpy)

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

 
#if STDC_HEADERS
# include <string.h>
#else
# if !HAVE_STRCHR
#  define strchr index
#  define strrchr rindex
# endif
char *strchr (), *strrchr ();
# if !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, 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 compatible, then instead of including it, define the POSIX 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

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

The way to check if the system supports POSIX is:

 
#if HAVE_UNISTD_H
# include <sys/types.h>
# include <unistd.h>
#endif

#ifdef _POSIX_VERSION
/* Code for POSIX systems.  */
#endif

Macro: AC_HEADER_TIME
If a program may include both `time.h' and `sys/time.h', define TIME_WITH_SYS_TIME. On some older systems, `sys/time.h' includes `time.h', but `time.h' is not protected against multiple inclusion, so programs should not explicitly include both files. This macro is useful in programs that use, for example, struct timeval as well as struct tm. It is best used in conjunction with HAVE_SYS_TIME_H, which can be checked for using AC_CHECK_HEADERS(sys/time.h).

 
#if TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# if HAVE_SYS_TIME_H
#  include <sys/time.h>
# else
#  include <time.h>
# endif
#endif

Macro: AC_HEADER_TIOCGWINSZ
If the use of TIOCGWINSZ requires `<sys/ioctl.h>', then define GWINSZ_IN_SYS_IOCTL. Otherwise TIOCGWINSZ can be found in `<termios.h>'.

Use:

 
#if HAVE_TERMIOS_H
# include <termios.h>
#endif

#if GWINSZ_IN_SYS_IOCTL
# include <sys/ioctl.h>
#endif


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