These macros check for particular C functions—whether they exist, and in some cases how they respond when given certain arguments.
Check for the alloca function. Define HAVE_ALLOCA_H if
alloca.h defines a working alloca. If not, look for a
builtin alternative. If either method succeeds, define
HAVE_ALLOCA. Otherwise, set the output variable ALLOCA to
‘${LIBOBJDIR}alloca.o’ and define
C_ALLOCA (so programs can periodically call ‘alloca (0)’ to
garbage collect). This variable is separate from LIBOBJS so
multiple programs can share the value of ALLOCA without needing
to create an actual library, in case only some of them use the code in
LIBOBJS. The ‘${LIBOBJDIR}’ prefix serves the same
purpose as in LIBOBJS (see AC_LIBOBJ vs. LIBOBJS).
Source files that use alloca should start with a piece of code
like the following, to declare it properly.
#include <stdlib.h> #include <stddef.h> #ifdef HAVE_ALLOCA_H # include <alloca.h> #elif !defined alloca # ifdef __GNUC__ # define alloca __builtin_alloca # elif defined _MSC_VER # include <malloc.h> # define alloca _alloca # elif !defined HAVE_ALLOCA # ifdef __cplusplus extern "C" # endif void *alloca (size_t); # endif #endif
If you don’t want to maintain this piece of code in your package manually,
you can instead use the Gnulib module alloca-opt or alloca.
See Gnulib.
If the chown function is available and works (in particular, it
should accept -1 for uid and gid), define
HAVE_CHOWN. The result of this macro is cached in the
ac_cv_func_chown_works variable.
If you want a workaround, that is, a chown function that is
available and works, you can use the Gnulib module chown.
See Gnulib.
If the closedir function does not return a meaningful value,
define CLOSEDIR_VOID. Otherwise, callers ought to check its
return value for an error indicator.
Currently this test is implemented by running a test program. When
cross compiling the pessimistic assumption that closedir does not
return a meaningful value is made.
The result of this macro is cached in the ac_cv_func_closedir_void
variable.
This macro is obsolescent, as closedir returns a meaningful value
on current systems. New programs need not use this macro.
If the error_at_line function is not found, require an
AC_LIBOBJ replacement of ‘error’.
The result of this macro is cached in the ac_cv_lib_error_at_line
variable.
The AC_FUNC_ERROR_AT_LINE macro is obsolescent. New programs
should use Gnulib’s error module. See Gnulib.
If the fnmatch function conforms to Posix, define
HAVE_FNMATCH.
Unlike the other specific
AC_FUNC macros, AC_FUNC_FNMATCH does not replace a
broken/missing fnmatch. This is for historical reasons.
See AC_REPLACE_FNMATCH below.
The result of this macro is cached in the ac_cv_func_fnmatch_works
variable.
This macro is obsolescent. New programs should use Gnulib’s
fnmatch-posix module. See Gnulib.
Behave like AC_REPLACE_FNMATCH (replace) but also test
whether fnmatch supports GNU extensions. Detect common
implementation bugs, for example, the bugs in the GNU C
Library 2.1.
The result of this macro is cached in the ac_cv_func_fnmatch_gnu
variable.
This macro is obsolescent. New programs should use Gnulib’s
fnmatch-gnu module. See Gnulib.
This macro checks for the fork and vfork functions. If a
working fork is found, define HAVE_WORKING_FORK. This macro
checks whether fork is just a stub by trying to run it.
If vfork.h is found, define HAVE_VFORK_H. If a working
vfork is found, define HAVE_WORKING_VFORK. Otherwise,
define vfork to be fork for backward compatibility with
previous versions of autoconf. This macro checks for several known
errors in implementations of vfork and considers the system to not
have a working vfork if it detects any of them.
Since this macro defines vfork only for backward compatibility with
previous versions of autoconf you’re encouraged to define it
yourself in new code:
#ifndef HAVE_WORKING_VFORK # define vfork fork #endif
The results of this macro are cached in the ac_cv_func_fork_works
and ac_cv_func_vfork_works variables. In order to override the
test, you also need to set the ac_cv_func_fork and
ac_cv_func_vfork variables.
If the fseeko and ftello functions are available, define
HAVE_FSEEKO. Define _LARGEFILE_SOURCE if necessary to
make the prototype visible.
Configure scripts that use AC_FUNC_FSEEKO should normally also
use AC_SYS_LARGEFILE to ensure that off_t can represent
all supported file sizes. See AC_SYS_LARGEFILE.
The Gnulib module fseeko invokes AC_FUNC_FSEEKO
and also contains workarounds for other portability problems of
fseeko. See Gnulib.
Perform all the checks performed by AC_TYPE_GETGROUPS
(see AC_TYPE_GETGROUPS).
Then, if the getgroups function is available
and known to work correctly, define HAVE_GETGROUPS.
Set the output variable GETGROUPS_LIB to any libraries
needed to get that function.
This macro relies on a list of systems with known, serious bugs in
getgroups. If this list mis-identifies your system’s
getgroups as buggy, or as not buggy, you can override it by
setting the cache variable ac_cv_func_getgroups_works in a
config.site file (see Setting Site Defaults). Please also report the
error to the Autoconf Bugs mailing list.
The Gnulib module getgroups provides workarounds for additional,
less severe portability problems with this function.
Check how to get the system load averages. To perform its tests
properly, this macro needs the file getloadavg.c; therefore, be
sure to set the AC_LIBOBJ replacement directory properly (see
Generic Function Checks, AC_CONFIG_LIBOBJ_DIR).
If the system has the getloadavg function, define
HAVE_GETLOADAVG, and set GETLOADAVG_LIBS to any libraries
necessary to get that function. Also add GETLOADAVG_LIBS to
LIBS. Otherwise, require an AC_LIBOBJ replacement for
‘getloadavg’ and possibly define several other C preprocessor
macros and output variables:
C_GETLOADAVG.
SVR4, DGUX, UMAX, or UMAX4_3 if on
those systems.
HAVE_NLIST_H.
HAVE_STRUCT_NLIST_N_UN_N_NAME. The obsolete symbol
NLIST_NAME_UNION is still defined, but do not depend upon it.
getloadavg to work. In this case, define
GETLOADAVG_PRIVILEGED, set the output variable NEED_SETGID
to ‘true’ (and otherwise to ‘false’), and set
KMEM_GROUP to the name of the group that should own the installed
program.
The AC_FUNC_GETLOADAVG macro is obsolescent. New programs should
use Gnulib’s getloadavg module. See Gnulib.
Check for getmntent in the standard C library, and then in the
sun, seq, and gen libraries, for UNICOS,
IRIX 4, PTX, and UnixWare, respectively. Then, if
getmntent is available, define HAVE_GETMNTENT and set
ac_cv_func_getmntent to yes. Otherwise set
ac_cv_func_getmntent to no.
The result of this macro can be overridden by setting the cache variable
ac_cv_search_getmntent.
The AC_FUNC_GETMNTENT macro is obsolescent. New programs should
use Gnulib’s mountlist module. See Gnulib.
Define GETPGRP_VOID if it is an error to pass 0 to
getpgrp; this is the Posix behavior. On older BSD
systems, you must pass 0 to getpgrp, as it takes an argument and
behaves like Posix’s getpgid.
#ifdef GETPGRP_VOID pid = getpgrp (); #else pid = getpgrp (0); #endif
This macro does not check whether
getpgrp exists at all; if you need to work in that situation,
first call AC_CHECK_FUNC for getpgrp.
The result of this macro is cached in the ac_cv_func_getpgrp_void
variable.
This macro is obsolescent, as current systems have a getpgrp
whose signature conforms to Posix. New programs need not use this macro.
If link is a symbolic link, then lstat should treat
link/ the same as link/.. However, many older
lstat implementations incorrectly ignore trailing slashes.
It is safe to assume that if lstat incorrectly ignores
trailing slashes, then other symbolic-link-aware functions like
unlink also incorrectly ignore trailing slashes.
If lstat behaves properly, define
LSTAT_FOLLOWS_SLASHED_SYMLINK, otherwise require an
AC_LIBOBJ replacement of lstat.
The result of this macro is cached in the
ac_cv_func_lstat_dereferences_slashed_symlink variable.
The AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK macro is obsolescent.
New programs should use Gnulib’s lstat module. See Gnulib.
If the malloc function is compatible with the GNU C
library malloc (i.e., ‘malloc (0)’ returns a valid
pointer), define HAVE_MALLOC to 1. Otherwise define
HAVE_MALLOC to 0, ask for an AC_LIBOBJ replacement for
‘malloc’, and define malloc to rpl_malloc so that the
native malloc is not used in the main project.
Typically, the replacement file malloc.c should look like (note the ‘#undef malloc’):
#include <config.h>
#undef malloc
#include <stdlib.h>
/* Allocate an N-byte block of memory from the heap.
If N is zero, allocate a 1-byte block. */
void *
rpl_malloc (size_t n)
{
if (n == 0)
n = 1;
return malloc (n);
}
The result of this macro is cached in the
ac_cv_func_malloc_0_nonnull variable.
If you don’t want to maintain a malloc.c file in your package
manually, you can instead use the Gnulib module malloc-gnu.
Define HAVE_MBRTOWC to 1 if the function mbrtowc and the
type mbstate_t are properly declared.
The result of this macro is cached in the ac_cv_func_mbrtowc
variable.
The Gnulib module mbrtowc not only ensures that the
function is declared, but also works around other portability
problems of this function.
If the memcmp function is not available or does not work, require an
AC_LIBOBJ replacement for ‘memcmp’.
The result of this macro is cached in the
ac_cv_func_memcmp_working variable.
This macro is obsolescent, as current systems have a working
memcmp. New programs need not use this macro.
If the mktime function is not available, or does not work
correctly, require an AC_LIBOBJ replacement for ‘mktime’.
For the purposes of this test, mktime should conform to the
Posix standard and should be the inverse of
localtime.
The result of this macro is cached in the
ac_cv_func_working_mktime variable.
The AC_FUNC_MKTIME macro is obsolescent. New programs should
use Gnulib’s mktime module. See Gnulib.
If the mmap function exists and works correctly, define
HAVE_MMAP. This checks only private fixed mapping of already-mapped
memory.
The result of this macro is cached in the
ac_cv_func_mmap_fixed_mapped variable.
Note: This macro asks for more than what an average program needs from
mmap. In particular, the use of MAP_FIXED fails on
HP-UX 11, whereas mmap otherwise works fine on this platform.
If the obstacks are found, define HAVE_OBSTACK, else require an
AC_LIBOBJ replacement for ‘obstack’.
The result of this macro is cached in the ac_cv_func_obstack
variable.
The AC_FUNC_OBSTACK macro is obsolescent. New programs should use
Gnulib’s obstack module. See Gnulib.
If the realloc function is compatible with the GNU C
library realloc (i.e., ‘realloc (NULL, 0)’ returns a
valid pointer), define HAVE_REALLOC to 1. Otherwise define
HAVE_REALLOC to 0, ask for an AC_LIBOBJ replacement for
‘realloc’, and define realloc to rpl_realloc so that
the native realloc is not used in the main project. See
AC_FUNC_MALLOC for details.
The result of this macro is cached in the
ac_cv_func_realloc_0_nonnull variable.
If you don’t want to maintain a realloc.c file in your package
manually, you can instead use the Gnulib module realloc-gnu.
Determines the correct type to be passed for each of the
select function’s arguments, and defines those types
in SELECT_TYPE_ARG1, SELECT_TYPE_ARG234, and
SELECT_TYPE_ARG5 respectively. SELECT_TYPE_ARG1 defaults
to ‘int’, SELECT_TYPE_ARG234 defaults to ‘int *’,
and SELECT_TYPE_ARG5 defaults to ‘struct timeval *’.
This macro is obsolescent, as current systems have a select whose
signature conforms to Posix. New programs need not use this macro.
If setpgrp takes no argument (the Posix version), define
SETPGRP_VOID. Otherwise, it is the BSD version, which takes
two process IDs as arguments. This macro does not check whether
setpgrp exists at all; if you need to work in that situation,
first call AC_CHECK_FUNC for setpgrp. This macro also
does not check for the Solaris variant of setpgrp, which returns
a pid_t instead of an int; portable code should only use
the return value by comparing it against -1 to check for errors.
The result of this macro is cached in the ac_cv_func_setpgrp_void
variable.
This macro is obsolescent, as all forms of setpgrp are also
obsolescent. New programs should use the Posix function setpgid,
which takes two process IDs as arguments (like the BSD setpgrp).
Determine whether stat or lstat have the bug that it
succeeds when given the zero-length file name as argument.
If it does, then define HAVE_STAT_EMPTY_STRING_BUG (or
HAVE_LSTAT_EMPTY_STRING_BUG) and ask for an AC_LIBOBJ
replacement of it.
The results of these macros are cached in the
ac_cv_func_stat_empty_string_bug and the
ac_cv_func_lstat_empty_string_bug variables, respectively.
These macros are obsolescent, as no current systems have the bug. New programs need not use these macros.
If the strcoll function exists and works correctly, define
HAVE_STRCOLL. This does a bit more than
‘AC_CHECK_FUNCS(strcoll)’, because some systems have incorrect
definitions of strcoll that should not be used. But it does
not check against a known bug of this function on Solaris 10.
The result of this macro is cached in the ac_cv_func_strcoll_works
variable.
If strerror_r is available, define HAVE_STRERROR_R, and if
it is declared, define HAVE_DECL_STRERROR_R. If it returns a
char * message, define STRERROR_R_CHAR_P; otherwise it
returns an int error number. The Thread-Safe Functions option of
Posix requires strerror_r to return int, but
many systems (including, for example, version 2.2.4 of the GNU C
Library) return a char * value that is not necessarily equal to
the buffer argument.
The result of this macro is cached in the
ac_cv_func_strerror_r_char_p variable.
The Gnulib module strerror_r not only ensures that the function
has the return type specified by Posix, but also works around other
portability problems of this function.
Check for strftime in the intl library, for SCO Unix.
Then, if strftime is available, define HAVE_STRFTIME.
This macro is obsolescent, as no current systems require the intl
library for strftime. New programs need not use this macro.
If the strtod function does not exist or doesn’t work correctly,
ask for an AC_LIBOBJ replacement of ‘strtod’. In this case,
because strtod.c is likely to need ‘pow’, set the output
variable POW_LIB to the extra library needed.
This macro caches its result in the ac_cv_func_strtod variable
and depends upon the result in the ac_cv_func_pow variable.
The AC_FUNC_STRTOD macro is obsolescent. New programs should
use Gnulib’s strtod module. See Gnulib.
If the strtold function exists and conforms to C99 or later, define
HAVE_STRTOLD.
This macro caches its result in the ac_cv_func_strtold variable.
The Gnulib module strtold not only ensures that the
function exists, but also works around other portability
problems of this function.
If the strnlen function is not available, or is buggy (like the one
from AIX 4.3), require an AC_LIBOBJ replacement for it.
This macro caches its result in the ac_cv_func_strnlen_working
variable.
The AC_FUNC_STRNLEN macro is obsolescent. New programs should
use Gnulib’s strnlen module. See Gnulib.
If ‘utime (file, NULL)’ sets file’s timestamp to
the present, define HAVE_UTIME_NULL.
This macro caches its result in the ac_cv_func_utime_null
variable.
This macro is obsolescent, as all current systems have a utime
that behaves this way. New programs need not use this macro.
If vprintf is found, define HAVE_VPRINTF. Otherwise, if
_doprnt is found, define HAVE_DOPRNT. (If vprintf
is available, you may assume that vfprintf and vsprintf
are also available.)
This macro is obsolescent, as all current systems have vprintf.
New programs need not use this macro.
If the fnmatch function does not conform to Posix (see
AC_FUNC_FNMATCH), ask for its AC_LIBOBJ replacement.
The files fnmatch.c, fnmatch_loop.c, and fnmatch_.h
in the AC_LIBOBJ replacement directory are assumed to contain a
copy of the source code of GNU fnmatch. If necessary,
this source code is compiled as an AC_LIBOBJ replacement, and the
fnmatch_.h file is linked to fnmatch.h so that it can be
included in place of the system <fnmatch.h>.
This macro caches its result in the ac_cv_func_fnmatch_works
variable.
This macro is obsolescent, as it assumes the use of particular source
files. New programs should use Gnulib’s fnmatch-posix module,
which provides this macro along with the source files. See Gnulib.