GNU Info
(autoconf.info)Particular Headers
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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