These macros test for particular system features that packages might need or want to use. If you need to test for a kind of feature that none of these macros check for, you can probably do it by calling primitive test macros with appropriate arguments (see section Writing Tests).
These tests print messages telling the user which feature they're
checking for, and what they find. They cache their results for future
configure runs (see section Caching Results).
Some of these macros set output variables. See section Substitutions in Makefiles, for how to get their values. The phrase "define name" is used below as a shorthand to mean "define C preprocessor symbol name to the value 1". See section Defining C Preprocessor Symbols, for how to get those symbol definitions into your program.
typedefs that might be missing.
These macros check for the presence or behavior of particular programs. They are used to choose between several alternative programs and to decide what to do once one has been chosen. If there is no macro specifically defined to check for a program you need, and you don't need to check for any special properties of it, then you can use one of the general program check macros.
These macros check for particular programs--whether they exist, and in some cases whether they support certain features.
YYTEXT_POINTER if yytext is a `char *' instead
of a `char []'. Also set output variable LEX_OUTPUT_ROOT to
the base of the file name that the lexer generates; usually
`lex.yy', but sometimes something else. These results vary
according to whether lex or flex is being used.
mawk, gawk, nawk, and awk, in that
order, and set output variable AWK to the first one that it
finds. It tries mawk first because that is reported to be the
fastest implementation.
CC is not already set in the
environment, check for gcc, and use cc if it's not found.
Set output variable CC to the name of the compiler found.
If using the GNU C compiler, set shell variable GCC to
`yes', empty otherwise. If output variable CFLAGS was
not already set, set it to `-g -O' for the GNU C compiler
(`-O' on systems where GCC does not accept `-g'), or `-g'
for other compilers.
NO_MINUS_C_MINUS_O.
CPP to a command that runs the
C preprocessor. If `$CC -E' doesn't work, it uses `/lib/cpp'.
It is only portable to run CPP on files with a `.c'
extension.
If the current language is C (see section Language Choice), many of the
specific test macros use the value of CPP indirectly by calling
AC_TRY_CPP, AC_CHECK_HEADER, AC_EGREP_HEADER, or
AC_EGREP_CPP.
CXX or CCC (in that order) is set; if so, set output
variable CXX to its value. Otherwise search for a C++ compiler
under likely names (c++, g++, gcc, CC, and
cxx). If none of those checks succeed, as a last resort set
CXX to gcc.
If using the GNU C++ compiler, set shell variable GXX to
`yes', empty otherwise. If output variable CXXFLAGS was
not already set, set it to `-g -O' for the GNU C++ compiler
(`-O' on systems where G++ does not accept `-g'), or `-g'
for other compilers.
CXXCPP to a command that runs the
C++ preprocessor. If `$CXX -E' doesn't work, it uses `/lib/cpp'.
It is only portable to run CXXCPP on files with a `.c',
`.C', or `.cc' extension.
If the current language is C++ (see section Language Choice), many of the
specific test macros use the value of CXXCPP indirectly by
calling AC_TRY_CPP, AC_CHECK_HEADER,
AC_EGREP_HEADER, or AC_EGREP_CPP.
CC if using the
GNU C compiler and ioctl does not work properly without
`-traditional'. That usually happens when the fixed header files
have not been installed on an old system. Since recent versions of the
GNU C compiler fix the header files automatically when installed, this
is becoming a less prevalent problem.
INSTALL to the path of a BSD compatible
install program, if one is found in the current PATH.
Otherwise, set INSTALL to `dir/install-sh -c',
checking the directories specified to AC_CONFIG_AUX_DIR (or its
default directories) to determine dir (see section Creating Output Files). Also set
the variable INSTALL_PROGRAM to `${INSTALL}' and
INSTALL_DATA to `${INSTALL} -m 644'.
This macro screens out various instances of install known to not
work. It prefers to find a C program rather than a shell script, for
speed. Instead of `install-sh', it can also use `install.sh',
but that name is obsolete because some make programs have a rule
that creates `install' from it if there is no `Makefile'.
A copy of `install-sh' which you may use comes with Autoconf. If
you use AC_PROG_INSTALL, you must include either
`install-sh' or `install.sh' in your distribution, or
configure will produce an error message saying it can't find
them--even if the system you're on has a good install program.
This check is a safety measure to prevent you from accidentally leaving
that file out, which would prevent your package from installing on
systems that don't have a BSD-compatible install program.
If you need to use your own installation program because it has
features not found in standard install programs, there is no
reason to use AC_PROG_INSTALL; just put the pathname of your
program into your `Makefile.in' files.
flex is found, set output variable LEX to
`flex' and LEXLIB to `-lfl', if that library is in a
standard place. Otherwise set LEX to `lex' and
LEXLIB to `-ll'.
LN_S to `ln -s', otherwise set it to `ln'.
RANLIB to `ranlib' if ranlib
is found, otherwise to `:' (do nothing).
bison is found, set output variable YACC to
`bison -y'. Otherwise, if byacc is found, set YACC
to `byacc'. Otherwise set YACC to `yacc'.
These macros are used to find programs not covered by the particular
test macros. If you need to check the behavior of a program as well as
find out whether it is present, you have to write your own test for it
(see section Writing Tests). By default, these macros use the environment
variable PATH. If you need to check for a program that might not
be in the user's PATH, you can pass a modified path to use
instead, like this:
AC_PATH_PROG(INETD, inetd, /usr/libexec/inetd, $PATH:/usr/libexec:/usr/sbin:/usr/etc:etc)
PATH. If
it is found, set variable to value-if-found, otherwise to
value-if-not-found, if given. If variable was already set,
do nothing. Calls AC_SUBST for variable.
PATH. If it is found, set
variable to the name of that program. Otherwise, continue
checking the next program in the list. If none of the programs in the
list are found, set variable to value-if-not-found; if
value-if-not-found is not specified, the value of variable
is not changed. Calls AC_SUBST for variable.
AC_CHECK_PROG, but first looks for prog-to-check-for
with a prefix of the host type as determined by AC_CANONICAL_HOST,
followed by a dash (see section Getting the Canonical System Type). For example, if the user
runs `configure --host=i386-gnu', then this call:
AC_CHECK_TOOL(RANLIB, ranlib, :)
sets RANLIB to `i386-gnu-ranlib' if that program exists in
PATH, or to `ranlib' if that program exists in PATH,
or to `:' if neither program exists.
AC_CHECK_PROG, but set variable to the entire
path of prog-to-check-for if found.
AC_CHECK_PROGS, but if any of progs-to-check-for
are found, set variable to the entire path of the program
found.
The following macros check for the presence of certain C library archive files.
action-if-found is a list of shell commands to run if the link
with the library succeeds; action-if-not-found is a list of shell
commands to run if the link fails. If action-if-found and
action-if-not-found are not specified, the default action is to
add `-llibrary' to LIBS and define
`HAVE_LIBlibrary' (in all capitals).
If linking with library results in unresolved symbols, which would be resolved by linking with additional libraries, give those libraries as the other-libraries argument, separated by spaces: `-lXt -lX11'. Otherwise this macro will fail to detect that library is present, because linking the test program will always fail with unresolved symbols.
AC_CHECK_LIB with a
function argument of main. In addition, library can
be written as any of `foo', `-lfoo', or `libfoo.a'. In
all of those cases, the compiler is passed `-lfoo'. However,
library can not be a shell variable; it must be a literal name.
This macro is considered obsolete.
The following macros check for particular C library functions. If there is no macro specifically defined to check for a function you need, and you don't need to check for any special properties of it, then you can use one of the general function check macros.
These macros check for particular C functions--whether they exist, and in some cases how they respond when given certain arguments.
alloca. Tries to get a builtin version by
checking for `alloca.h' or the predefined C preprocessor macros
__GNUC__ and _AIX. If this macro finds `alloca.h',
it defines HAVE_ALLOCA_H.
If those attempts fail, it looks for the function in the standard C
library. If any of those methods succeed, it defines
HAVE_ALLOCA. Otherwise, it sets the output variable
ALLOCA to `alloca.o' and defines 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.
This macro does not try to get alloca from the System V R3
`libPW' or the System V R4 `libucb' because those libraries
contain some incompatible functions that cause trouble. Some versions
do not even contain alloca or contain a buggy version. If you
still want to use their alloca, use ar to extract
`alloca.o' from them instead of compiling `alloca.c'.
Source files that use alloca should start with a piece of code
like the following, to declare it properly. In some versions
of AIX, the declaration of alloca must precede everything else
except for comments and preprocessor directives. The #pragma
directive is indented so that pre-ANSI C compilers will ignore it,
rather than choke on it.
/* AIX requires this to be the first thing in the file. */ #ifdef __GNUC__ # define alloca __builtin_alloca #else # if HAVE_ALLOCA_H # include <alloca.h> # else # ifdef _AIX #pragma alloca # else # ifndef alloca /* predefined by HP cc +Olibcalls */ char *alloca (); # endif # endif # endif #endif
closedir function does not return a meaningful value,
define CLOSEDIR_VOID. Otherwise, callers ought to check its
return value for an error indicator.
getloadavg function, this macro defines HAVE_GETLOADAVG,
and adds to LIBS any libraries needed to get that function.
Otherwise, it adds `getloadavg.o' to the output variable
LIBOBJS, and possibly defines several other C preprocessor
macros and output variables:
SVR4, DGUX, UMAX, or UMAX4_3 if
on those systems.
NLIST_STRUCT.
NLIST_NAME_UNION.
LDAV_PRIVILEGED,
programs need to be installed specially on this system for
getloadavg to work, and this macro defines
GETLOADAVG_PRIVILEGED.
NEED_SETGID. The value is
`true' if special installation is required, `false' if not.
If NEED_SETGID is `true', this macro sets KMEM_GROUP
to the name of the group that should own the installed program.
getmntent in the `sun', `seq', and `gen'
libraries, for Irix 4, PTX, and Unixware, respectively. Then, if
getmntent is available, define HAVE_GETMNTENT.
getpgrp takes no argument (the POSIX.1 version), define
GETPGRP_VOID. Otherwise, it is the BSD version, which takes a
process ID as an argument. 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.
memcmp function is not available, or does not work on
8-bit data (like the one on SunOS 4.1.3), add `memcmp.o' to output
variable LIBOBJS.
mmap function exists and works correctly on memory mapped
files, define HAVE_MMAP.
setvbuf takes the buffering type as its second argument and
the buffer pointer as the third, instead of the other way around, define
SETVBUF_REVERSED. This is the case on System V before release 3.
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, which should not be used.
strftime in the `intl' library, for SCO UNIX.
Then, if strftime is available, define HAVE_STRFTIME.
HAVE_UTIME_NULL.
HAVE_VFORK_H. If a working
vfork is not found, define vfork to be fork. 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. It is not considered to be an implementation error
if a child's invocation of signal modifies the parent's signal
handler, since child processes rarely change their signal handlers.
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.)
wait3 is found and fills in the contents of its third argument
(a `struct rusage *'), which HP-UX does not do, define
HAVE_WAIT3.
These macros are used to find functions not covered by the particular
test macros. If the functions might be in libraries other than the
default C library, first call AC_CHECK_LIB for those libraries.
If you need to check the behavior of a function as well as find out
whether it is present, you have to write your own test for
it (see section Writing Tests).
AC_CHECK_FUNCS instead. This macro checks for functions with C
linkage even when AC_LANG_CPLUSPLUS has been called, since C++ is
more standardized than C is. (see section Language Choice, for more
information about selecting the language for checks.)
HAVE_function (in all capitals). If
action-if-found is given, it is additional shell code to execute
when one of the functions is found. You can give it a value of
`break' to break out of the loop on the first match. If
action-if-not-found is given, it is executed when one of the
functions is not found.
LIBOBJS.
The following macros check for the presence of certain C header files. If there is no macro specifically defined to check for a header file you need, and you don't need to check for any special properties of it, then you can use one of the general header file check macros.
These macros check for particular system header files--whether they exist, and in some cases whether they declare certain symbols.
SYS_SIGLIST_DECLARED if the variable sys_siglist is
declared in a system header file, either `signal.h' or
`unistd.h'.
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
SYSNDIR
SYSDIR
NDIR
In addition, if the closedir function does not return a
meaningful value, define VOID_CLOSEDIR.
HAVE_DIRENT_H
HAVE_SYS_NDIR_H
HAVE_SYS_DIR_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.
major, minor, and
makedev, but `sys/mkdev.h' does, define
MAJOR_IN_MKDEV; otherwise, if `sys/sysmacros.h' does, define
MAJOR_IN_SYSMACROS.
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)'.
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
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.
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'.
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.
These macros are used to find system header files not covered by the particular test macros. If you need to check the contents of a header as well as find out whether it is present, you have to write your own test for it (see section Writing Tests).
AC_CHECK_HEADERS instead.
HAVE_header-file (in all capitals). If action-if-found
is given, it is additional shell code to execute when one of the header
files is found. You can give it a value of `break' to break out of
the loop on the first match. If action-if-not-found is given, it
is executed when one of the header files is not found.
The following macros check for certain structures or structure members.
To check structures not listed here, use AC_EGREP_CPP
(see section Examining Declarations) or AC_TRY_COMPILE
(see section Examining Syntax).
S_ISDIR, S_ISREG et al. 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.
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 or struct timezone 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
struct stat contains an st_blksize member, define
HAVE_ST_BLKSIZE.
struct stat contains an st_blocks member, define
HAVE_ST_BLOCKS. Otherwise, add `fileblocks.o' to the
output variable LIBOBJS.
struct stat contains an st_rdev member, define
HAVE_ST_RDEV.
struct tm, define
TM_IN_SYS_TIME, which means that including `sys/time.h'
had better define struct tm.
struct tm has a
tm_zone member, define HAVE_TM_ZONE. Otherwise, if the
external array tzname is found, define HAVE_TZNAME.
The following macros check for C typedefs. If there is no macro specifically defined to check for a typedef you need, and you don't need to check for any special properties of it, then you can use a general typedef check macro.
These macros check for particular C typedefs in `sys/types.h' and `stdlib.h' (if it exists).
GETGROUPS_T to be whichever of gid_t or int
is the base type of the array argument to getgroups.
mode_t is not defined, define mode_t to be int.
off_t is not defined, define off_t to be long.
pid_t is not defined, define pid_t to be int.
signal as returning a pointer to a
function returning void, define RETSIGTYPE to be
void; otherwise, define it to be int.
Define signal handlers as returning type RETSIGTYPE:
RETSIGTYPE
hup_handler ()
{
...
}
size_t is not defined, define size_t to be
unsigned.
uid_t is not defined, define uid_t to be int and
gid_t to be int.
This macro is used to check for typedefs not covered by the particular test macros.
The following macros check for C compiler or machine architecture
features. To check for characteristics not listed here, use
AC_TRY_COMPILE (see section Examining Syntax) or AC_TRY_RUN
(see section Checking Run Time Behavior)
WORDS_BIGENDIAN.
const,
define const to be empty. Some C compilers that do not define
__STDC__ do support const; some compilers that define
__STDC__ do not completely support const. Programs can
simply use const as if every C compiler supported it; for those
that don't, the `Makefile' or configuration header file will define
it as empty.
inline, do nothing.
Otherwise define inline to __inline__ or __inline
if it accepts one of those, otherwise define inline to be empty.
char is unsigned, define __CHAR_UNSIGNED__,
unless the C compiler predefines it.
long double type, define
HAVE_LONG_DOUBLE. Some C compilers that do not define
__STDC__ do support the long double type; some compilers
that define __STDC__ do not support long double.
SIZEOF_uctype to be the size in bytes of the C (or
C++) builtin type type, e.g. `int' or `char *'. If
`type' is unknown to the compiler, it gets a size of 0. uctype
is type, with lowercase converted to uppercase, spaces changed to
underscores, and asterisks changed to `P'. If cross-compiling, the
value cross-size is used if given, otherwise configure
exits with an error message.
For example, the call
AC_CHECK_SIZEOF(int *)
defines SIZEOF_INT_P to be 8 on DEC Alpha AXP systems.
int is 16 bits wide, define INT_16_BITS.
This macro is obsolete; it is more general to use
`AC_CHECK_SIZEOF(int)' instead.
long int is 64 bits wide, define
LONG_64_BITS. This macro is obsolete; it is more general to use
`AC_CHECK_SIZEOF(long)' instead.
The following macros check for operating system services or capabilities.
configure.in can check
the variable ac_cv_sys_interpreter; it will be set to `yes'
if the system supports `#!', `no' if not.
xmkmf on a
trivial `Imakefile' and examining the `Makefile' that it
produces. If that fails (such as if xmkmf is not present), look
for them in several directories where they often reside. If either
method is successful, set the shell variables x_includes and
x_libraries to their locations, unless they are in directories
the compiler searches by default.
If both methods fail, or the user gave the command line option
`--without-x', set the shell variable no_x to `yes';
otherwise set it to the empty string.
AC_PATH_X. It adds the C compiler flags that
X needs to output variable X_CFLAGS, and the X linker flags to
X_LIBS. If X is not available, adds `-DX_DISPLAY_MISSING' to
X_CFLAGS.
This macro also checks for special libraries that some systems need in
order to compile X programs. It adds any that the system needs to
output variable X_EXTRA_LIBS. And it checks for special X11R6
libraries that need to be linked with before `-lX11', and adds any
found to the output variable X_PRE_LIBS.
HAVE_LONG_FILE_NAMES.
HAVE_RESTARTABLE_SYSCALLS.
The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide.
_ALL_SOURCE. Allows the use of some BSD
functions. Should be called before any macros that run the C compiler.
LIBS. This macro is obsolete; instead, use
AC_FUNC_GETMNTENT.
LIBS. This macro is obsolete. If you were using it to get
getmntent, use AC_FUNC_GETMNTENT instead. If you used it
for the NIS versions of the password and group functions, use
`AC_CHECK_LIB(sun, getpwnam)'.
_POSIX_SOURCE and add
`-posix' (for the GNU C compiler) or `-Xp' (for other C
compilers) to output variable CC. This allows the use of
POSIX facilities. Must be called after AC_PROG_CC and before
any other macros that run the C compiler.
_MINIX and _POSIX_SOURCE and define
_POSIX_1_SOURCE to be 2. This allows the use of POSIX
facilities. Should be called before any macros that run the C compiler.
LIBS.
This macro is obsolete; instead, use AC_FUNC_STRFTIME.
LIBS. Also, if
`dirent.h' is being used, add `-ldir' to LIBS. This
macro is obsolete; use AC_HEADER_DIRENT instead.