configure Scripts
configure Scripts
A physicist, an engineer, and a computer scientist were discussing the nature of God. Surely a Physicist, said the physicist, because early in the Creation, God made Light; and you know, Maxwell's equations, the dual nature of electro-magnetic waves, the relativist consequences... An Engineer!, said the engineer, because before making Light, God split the Chaos into Land and Water; it takes a hell of an engineer to handle that big amount of mud, and orderly separation of solids from liquids... The computer scientist shouted: And the Chaos, where do you think it was coming from, hmm? ---Anonymous
Autoconf is a tool for producing shell scripts that automatically configure software source code packages to adapt to many kinds of UNIX-like systems. The configuration scripts produced by Autoconf are independent of Autoconf when they are run, so their users do not need to have Autoconf.
The configuration scripts produced by Autoconf require no manual user intervention when run; they do not normally even need an argument specifying the system type. Instead, they test for the presence of each feature that the software package they are for might need individually. (Before each check, they print a one-line message stating what they are checking for, so the user doesn't get too bored while waiting for the script to finish.) As a result, they deal well with systems that are hybrids or customized from the more common UNIX variants. There is no need to maintain files that list the features supported by each release of each variant of UNIX.
For each software package that Autoconf is used with, it creates a configuration script from a template file that lists the system features that the package needs or can use. After the shell code to recognize and respond to a system feature has been written, Autoconf allows it to be shared by many software packages that can use (or need) that feature. If it later turns out that the shell code needs adjustment for some reason, it needs to be changed in only one place; all of the configuration scripts can be regenerated automatically to take advantage of the updated code.
The Metaconfig package is similar in purpose to Autoconf, but the scripts it produces require manual user intervention, which is quite inconvenient when configuring large source trees. Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling, if some care is taken in writing them.
There are several jobs related to making portable software packages that Autoconf currently does not do. Among these are automatically creating `Makefile' files with all of the standard targets, and supplying replacements for standard library functions and header files on systems that lack them. Work is in progress to add those features in the future.
Autoconf imposes some restrictions on the names of macros used with
#ifdef in C programs (see section Preprocessor Symbol Index).
Autoconf requires GNU m4 in order to generate the scripts. It
uses features that some UNIX versions of m4 do not have. It also
overflows internal limits of some versions of m4, including GNU
m4 1.0. You must use version 1.1 or later of GNU m4.
Using version 1.3 or later will be much faster than 1.1 or 1.2.
See section Upgrading From Version 1, for information about upgrading from version 1. See section History of Autoconf, for the story of Autoconf's development. See section Questions About Autoconf, for answers to some common questions about Autoconf.
Mail suggestions and bug reports for Autoconf to
bug-gnu-utils@prep.ai.mit.edu. Please include the Autoconf version
number, which you can get by running `autoconf --version'.
configure Scripts
The configuration scripts that Autoconf produces are by convention
called configure. When run, configure creates several
files, replacing configuration parameters in them with appropriate
values. The files that configure creates are:
#define directives (see section Configuration Header Files);
configure makes a mistake.
To create a configure script with Autoconf, you need to write an
Autoconf input file `configure.in' and run autoconf on it.
If you write your own feature tests to supplement those that come with
Autoconf, you might also write files called `aclocal.m4' and
`acsite.m4'. If you use a C header file to contain #define
directives, you might also write `acconfig.h', and you will
distribute the Autoconf-generated file `config.h.in' with the
package.
Here is a diagram showing how the files that can be used in
configuration are produced. Programs that are executed are suffixed by
`*'. Optional files are enclosed in square brackets (`[]').
autoconf and autoheader also read the installed Autoconf
macro files (by reading `autoconf.m4').
Files used in preparing a software package for distribution:
your source files --> [autoscan*] --> [configure.scan] --> configure.in
configure.in --. .------> autoconf* -----> configure
+---+
[aclocal.m4] --+ `---.
[acsite.m4] ---' |
+--> [autoheader*] -> [config.h.in]
[acconfig.h] ----. |
+-----'
[config.h.top] --+
[config.h.bot] --'
Makefile.in -------------------------------> Makefile.in
Files used in configuring a software package:
.-------------> config.cache
configure* ------------+-------------> config.log
|
[config.h.in] -. v .-> [config.h] -.
+--> config.status* -+ +--> make*
Makefile.in ---' `-> Makefile ---'
To produce a configure script for a software package, create a
file called `configure.in' that contains invocations of the
Autoconf macros that test the system features your package needs or can
use. Autoconf macros already exist to check for many features; see
section Existing Tests, for their descriptions. For most other
features, you can use Autoconf template macros to produce custom checks;
see section Writing Tests, for information about them. For especially
tricky or specialized features, `configure.in' might need to
contain some hand-crafted shell commands. The autoscan
program can give you a good start in writing `configure.in'
(see section Using autoscan to Create `configure.in', for more information).
The order in which `configure.in' calls the Autoconf macros
is not important, with a few exceptions. Every
`configure.in' must contain a call to AC_INIT before
the checks, and a call to AC_OUTPUT at the end
(see section Creating Output Files). Additionally, some macros rely on other macros
having been called first, because they check previously set
values of some variables to decide what to do. These macros are
noted in the individual descriptions (see section Existing Tests),
and they also warn you when creating configure if they are
called out of order.
To encourage consistency, here is a suggested order for calling the Autoconf macros. Generally speaking, the things near the end of this list could depend on things earlier in it. For example, library functions could be affected by typedefs and libraries.
AC_INIT(file)checks for programs checks for libraries checks for header files checks for typedefs checks for structures checks for compiler characteristics checks for library functions checks for system servicesAC_OUTPUT([file...])
It is best to put each macro call on its own line in
`configure.in'. Most of the macros don't add extra newlines; they
rely on the newline after the macro call to terminate the commands.
This approach makes the generated configure script a little
easier to read by not inserting lots of blank lines. It is generally
safe to set shell variables on the same line as a macro call, because
the shell allows assignments without intervening newlines.
When calling macros that take arguments, there must not be any blank
space between the macro name and the open parenthesis. Arguments can be
more than one line long if they are enclosed within the m4 quote
characters `[' and `]'. If you have a long line such as a
list of file names, you can generally use a backslash at the end of a
line to continue it logically on the next line (this is implemented by
the shell, not by anything special that Autoconf does).
Some macros handle two cases: what to do if the given condition is met, and what to do if the condition is not met. In some places you might want to do something if a condition is true but do nothing if it's false, or vice versa. To omit the true case, pass an empty value for the action-if-found argument to the macro. To omit the false case, omit the action-if-not-found argument to the macro, including the comma before it.
You can include comments in `configure.in' files by starting them
with the m4 builtin macro dnl, which discards text up
through the next newline. These comments do not appear in the generated
configure scripts. For example, it is helpful to begin
`configure.in' files with a line like this:
dnl Process this file with autoconf to produce a configure script.
autoscan to Create `configure.in'
The autoscan program can help you create a `configure.in'
file for a software package. autoscan examines source files in
the directory tree rooted at a directory given as a command line
argument, or the current directory if none is given. It searches the
source files for common portability problems and creates a file
`configure.scan' which is a preliminary `configure.in' for
that package.
You should manually examine `configure.scan' before renaming it to
`configure.in'; it will probably need some adjustments.
Occasionally autoscan outputs a macro in the wrong order relative
to another macro, so that autoconf produces a warning; you need
to move such macros manually. Also, if you want the package to use a
configuration header file, you must add a call to
AC_CONFIG_HEADER (see section Configuration Header Files). You might also
have to change or add some #if directives to your program in
order to make it work with Autoconf (see section Using ifnames to List Conditionals, for
information about a program that can help with that job).
autoscan uses several data files, which are installed along with the
distributed Autoconf macro files, to determine which macros to output
when it finds particular symbols in a package's source files. These
files all have the same format. Each line consists of a symbol,
whitespace, and the Autoconf macro to output if that symbol is
encountered. Lines starting with `#' are comments.
autoscan is only installed if you already have Perl installed.
autoscan accepts the following options:
--help
--macrodir=dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--verbose
--version
ifnames to List Conditionals
ifnames can help when writing a `configure.in' for a
software package. It prints the identifiers that the package already
uses in C preprocessor conditionals. If a package has already been set
up to have some portability, this program can help you figure out what
its configure needs to check for. It may help fill in some gaps
in a `configure.in' generated by autoscan (see section Using autoscan to Create `configure.in').
ifnames scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in #if, #elif, #ifdef, or #ifndef
directives. It prints each identifier on a line, followed by a
space-separated list of the files in which that identifier occurs.
ifnames accepts the following options:
--help
-h
--macrodir=dir
-m dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--version
autoconf to Create configure
To create configure from `configure.in', run the
autoconf program with no arguments. autoconf processes
`configure.in' with the m4 macro processor, using the
Autoconf macros. If you give autoconf an argument, it reads that
file instead of `configure.in' and writes the configuration script
to the standard output instead of to configure. If you give
autoconf the argument `-', it reads the standard input
instead of `configure.in' and writes the configuration script on
the standard output.
The Autoconf macros are defined in several files. Some of the files are
distributed with Autoconf; autoconf reads them first. Then it
looks for the optional file `acsite.m4' in the directory that
contains the distributed Autoconf macro files, and for the optional file
`aclocal.m4' in the current directory. Those files can contain
your site's or the package's own Autoconf macro definitions
(see section Writing Macros, for more information). If a macro is defined
in more than one of the files that autoconf reads, the last
definition it reads overrides the earlier ones.
autoconf accepts the following options:
--help
-h
--localdir=dir
-l dir
--macrodir=dir
-m dir
AC_MACRODIR environment variable to a directory; this
option overrides the environment variable.
--version
autoreconf to Update configure Scripts
If you have a lot of Autoconf-generated configure scripts, the
autoreconf program can save you some work. It runs
autoconf (and autoheader, where appropriate) repeatedly to
remake the Autoconf configure scripts and configuration header
templates in the directory tree rooted at the current directory. By
default, it only remakes those files that are older than their
`configure.in' or (if present) `aclocal.m4'. Since
autoheader does not change the timestamp of its output file if
the file wouldn't be changing, this is not necessarily the minimum
amount of work. If you install a new version of Autoconf, you can make
autoreconf remake all of the files by giving it the
`--force' option.
If you give autoreconf the `--macrodir=dir' or
`--localdir=dir' options, it passes them down to
autoconf and autoheader (with relative paths adjusted
properly).
autoreconf does not support having, in the same directory tree,
both directories that are parts of a larger package (sharing
`aclocal.m4' and `acconfig.h'), and directories that are
independent packages (each with their own `aclocal.m4' and
`acconfig.h'). It assumes that they are all part of the same
package, if you use `--localdir', or that each directory is a
separate package, if you don't use it. This restriction may be removed
in the future.
See section Automatic Remaking, for `Makefile' rules to automatically
remake configure scripts when their source files change. That
method handles the timestamps of configuration header templates
properly, but does not pass `--macrodir=dir' or
`--localdir=dir'.
autoreconf accepts the following options:
--help
-h
--force
-f
--localdir=dir
-l dir
autoconf and autoheader look for the package files
`aclocal.m4' and (autoheader only) `acconfig.h' (but
not `file.top' and `file.bot') in directory
dir instead of in the directory containing each `configure.in'.
--macrodir=dir
-m dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--verbose
autoreconf runs
autoconf (and autoheader, if appropriate).
--version
Autoconf-generated configure scripts need some information about
how to initialize, such as how to find the package's source files; and
about the output files to produce. The following sections describe
initialization and creating output files.
configure Input
Every configure script must call AC_INIT before doing
anything else. The only other required macro is AC_OUTPUT
(see section Creating Output Files).
configure checks for this file's existence to
make sure that the directory that it is told contains the source code in
fact does. Occasionally people accidentally specify the wrong directory
with `--srcdir'; this is a safety check. See section Running configure Scripts,
for more information.
Packages that do manual configuration or use the install program
might need to tell configure where to find some other shell
scripts by calling AC_CONFIG_AUX_DIR, though the default places
it looks are correct for most cases.
configure scripts that are in directory dir. These
are auxiliary files used in configuration. dir can be either
absolute or relative to `srcdir'. The default is
`srcdir' or `srcdir/..' or
`srcdir/../..', whichever is the first that contains
`install-sh'. The other files are not checked for, so that using
AC_PROG_INSTALL does not automatically require distributing the
other auxiliary files. It checks for `install.sh' also, but that
name is obsolete because some make programs have a rule that
creates `install' from it if there is no `Makefile'.
Every Autoconf-generated configure script must finish by calling
AC_OUTPUT. It is the macro that creates the `Makefile's and
optional other files resulting from configuration. The only other
required macro is AC_INIT (see section Finding configure Input).
If AC_CONFIG_HEADER, AC_LINK_FILES, or
AC_CONFIG_SUBDIRS has been called, this macro also creates the
files named as their arguments.
A typical call to AC_OUTPUT looks like this:
AC_OUTPUT(Makefile src/Makefile man/Makefile X/Imakefile)
You can override an input file name by appending to file a colon-separated list of input files. Examples:
AC_OUTPUT(Makefile:templates/top.mk lib/Makefile:templates/lib.mk) AC_OUTPUT(Makefile:templates/vars.mk:Makefile.in:templates/rules.mk)
Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file.
If you pass extra-cmds, those commands will be inserted into
`config.status' to be run after all its other processing. If
init-cmds are given, they are inserted just before
extra-cmds, with shell variable, command, and backslash
substitutions performed on them in configure. You can use
init-cmds to pass variables from configure to the
extra-cmds. If AC_OUTPUT_COMMANDS has been called, the
commands given to it are run just before the commands passed to this macro.
configure. This macro may be called multiple times.
Here is an unrealistic example:
fubar=27 AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.], fubar=$fubar) AC_OUTPUT_COMMANDS([echo this is another, extra, bit], [echo init bit])
If you run make on subdirectories, you should run it using the
make variable MAKE. Most versions of make set
MAKE to the name of the make program plus any options it
was given. (But many do not include in it the values of any variables
set on the command line, so those are not passed on automatically.)
Some old versions of make do not set this variable. The
following macro allows you to use it even with those versions.
make predefines the variable MAKE, define output
variable SET_MAKE to be empty. Otherwise, define SET_MAKE
to contain `MAKE=make'. Calls AC_SUBST for SET_MAKE.
To use this macro, place a line like this in each `Makefile.in'
that runs MAKE on other directories:
@SET_MAKE@
Each subdirectory in a distribution that contains something to be
compiled or installed should come with a file `Makefile.in', from
which configure will create a `Makefile' in that directory.
To create a `Makefile', configure performs a simple variable
substitution, replacing occurrences of `@variable@' in
`Makefile.in' with the value that configure has determined
for that variable. Variables that are substituted into output files in
this way are called output variables. They are ordinary shell
variables that are set in configure. To make configure
substitute a particular variable into the output files, the macro
AC_SUBST must be called with that variable name as an argument.
Any occurrences of `@variable@' for other variables are
left unchanged. See section Setting Output Variables, for more information on
creating output variables with AC_SUBST.
A software package that uses a configure script should be
distributed with a file `Makefile.in', but no `Makefile'; that
way, the user has to properly configure the package for the local system
before compiling it.
See section `Makefile Conventions' in The GNU Coding Standards, for more information on what to put in `Makefile's.
Some output variables are preset by the Autoconf macros. Some of the Autoconf macros set additional output variables, which are mentioned in the descriptions for those macros. See section Output Variable Index, for a complete list of output variables. Here is what each of the preset ones contains. See section `Variables for Installation Directories' in The GNU Coding Standards, for more information about the variables with names that end in `dir'.
configure and giving the name of the input file.
AC_OUTPUT adds a comment line containing this variable to the top
of every `Makefile' it creates. For other files, you should
reference this variable in a comment at the top of each input file. For
example, an input shell script should begin like this:
#! /bin/sh # @configure_input@
The presence of that line also reminds people editing the file that it
needs to be processed by configure in order to be used.
srcdir.
configure runs, the default value is set
when you call AC_PROG_CC (or empty if you don't). configure
uses this variable when compiling programs to test for C features.
configure runs, the default value is
empty. configure uses this variable when compiling or
preprocessing programs to test for C features.
configure runs, the default value is
set when you call AC_PROG_CXX (or empty if you don't).
configure uses this variable when compiling programs to test for
C++ features.
configure runs, the default
value is set when you call AC_PROG_F77 (or empty if you don't).
configure uses this variable when compiling programs to test for
Fortran 77 features.
AC_CONFIG_HEADER
is called, configure replaces `@DEFS@' with
`-DHAVE_CONFIG_H' instead (see section Configuration Header Files). This
variable is not defined while configure is performing its tests,
only when creating the output files. See section Setting Output Variables, for
how to check the results of previous tests.
configure runs,
the default value is empty. configure uses this variable when
linking programs to test for C features.
You can support compiling a software package for several architectures simultaneously from the same copy of the source code. The object files for each architecture are kept in their own directory.
To support doing this, make uses the VPATH variable to
find the files that are in the source directory. GNU make and
most other recent make programs can do this. Older make
programs do not support VPATH; when using them, the source code
must be in the same directory as the object files.
To support VPATH, each `Makefile.in' should contain two
lines that look like:
srcdir = @srcdir@ VPATH = @srcdir@
Do not set VPATH to the value of another variable, for example
`VPATH = $(srcdir)', because some versions of make do not do
variable substitutions on the value of VPATH.
configure substitutes in the correct value for srcdir when
it produces `Makefile'.
Do not use the make variable $<, which expands to the
pathname of the file in the source directory (found with VPATH),
except in implicit rules. (An implicit rule is one such as `.c.o',
which tells how to create a `.o' file from a `.c' file.) Some
versions of make do not set $< in explicit rules; they
expand it to an empty value.
Instead, `Makefile' command lines should always refer to source files by prefixing them with `$(srcdir)/'. For example:
time.info: time.texinfo
$(MAKEINFO) $(srcdir)/time.texinfo
You can put rules like the following in the top-level `Makefile.in' for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as `aclocal.m4' and those related to configuration header files. Omit from the `Makefile.in' rules any of these files that your package does not use.
The `${srcdir}/' prefix is included because of limitations in the
VPATH mechanism.
The `stamp-' files are necessary because the timestamps of
`config.h.in' and `config.h' will not be changed if remaking
them does not change their contents. This feature avoids unnecessary
recompilation. You should include the file `stamp-h.in' your
package's distribution, so make will consider `config.h.in'
up to date. On some old BSD systems, touch or any command that
results in an empty file does not update the timestamps, so use a
command like echo as a workaround.
${srcdir}/configure: configure.in aclocal.m4
cd ${srcdir} && autoconf
# autoheader might not change config.h.in, so touch a stamp file.
${srcdir}/config.h.in: stamp-h.in
${srcdir}/stamp-h.in: configure.in aclocal.m4 acconfig.h \
config.h.top config.h.bot
cd ${srcdir} && autoheader
echo timestamp > ${srcdir}/stamp-h.in
config.h: stamp-h
stamp-h: config.h.in config.status
./config.status
Makefile: Makefile.in config.status
./config.status
config.status: configure
./config.status --recheck
In addition, you should pass `echo timestamp > stamp-h' in the
extra-cmds argument to AC_OUTPUT, so `config.status'
will ensure that `config.h' is considered up to date.
See section Creating Output Files, for more information about AC_OUTPUT.
See section Recreating a Configuration, for more examples of handling configuration-related dependencies.
When a package tests more than a few C preprocessor symbols, the command
lines to pass `-D' options to the compiler can get quite long.
This causes two problems. One is that the make output is hard to
visually scan for errors. More seriously, the command lines can exceed
the length limits of some operating systems. As an alternative to
passing `-D' options to the compiler, configure scripts can
create a C header file containing `#define' directives. The
AC_CONFIG_HEADER macro selects this kind of output. It should be
called right after AC_INIT.
The package should `#include' the configuration header file before
any other header files, to prevent inconsistencies in declarations (for
example, if it redefines const). Use `#include <config.h>'
instead of `#include "config.h"', and pass the C compiler a
`-I.' option (or `-I..'; whichever directory contains
`config.h'). That way, even if the source directory is configured
itself (perhaps to make a distribution), other build directories can
also be configured without finding the `config.h' from the source
directory.
AC_OUTPUT create the file(s) in the whitespace-separated
list header-to-create containing C preprocessor #define
statements, and replace `@DEFS@' in generated files with
`-DHAVE_CONFIG_H' instead of the value of DEFS. The usual
name for header-to-create is `config.h'.
If header-to-create already exists and its contents are identical
to what AC_OUTPUT would put in it, it is left alone. Doing this
allows some changes in configuration without needlessly causing object
files that depend on the header file to be recompiled.
Usually the input file is named `header-to-create.in'; however, you can override the input file name by appending to header-to-create, a colon-separated list of input files. Examples:
AC_CONFIG_HEADER(defines.h:defines.hin) AC_CONFIG_HEADER(defines.h:defs.pre:defines.h.in:defs.post)
Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file.
Your distribution should contain a template file that looks as you want
the final header file to look, including comments, with default values
in the #define statements. For example, suppose your
`configure.in' makes these calls:
AC_CONFIG_HEADER(conf.h) AC_CHECK_HEADERS(unistd.h)
Then you could have code like the following in `conf.h.in'.
On systems that have `unistd.h', configure will change the 0
to a 1. On other systems, it will leave the line unchanged.
/* Define as 1 if you have unistd.h. */ #define HAVE_UNISTD_H 0
Alternately, if your code tests for configuration options using
#ifdef instead of #if, a default value can be to
#undef the variable instead of to define it to a value. On
systems that have `unistd.h', configure will change the
second line to read `#define HAVE_UNISTD_H 1'. On other systems,
it will comment that line out (in case the system predefines that
symbol).
/* Define if you have unistd.h. */ #undef HAVE_UNISTD_H
autoheader to Create `config.h.in'
The autoheader program can create a template file of C
`#define' statements for configure to use. If
`configure.in' invokes AC_CONFIG_HEADER(file),
autoheader creates `file.in'; if multiple file
arguments are given, the first one is used. Otherwise,
autoheader creates `config.h.in'.
If you give autoheader an argument, it uses that file instead of
`configure.in' and writes the header file to the standard output
instead of to `config.h.in'. If you give autoheader an
argument of `-', it reads the standard input instead of
`configure.in' and writes the header file to the standard output.
autoheader scans `configure.in' and figures out which C
preprocessor symbols it might define. It copies comments and
#define and #undef statements from a file called
`acconfig.h', which comes with and is installed with Autoconf. It
also uses a file called `acconfig.h' in the current directory, if
present. If you AC_DEFINE any additional symbols, you must
create that file with entries for them. For symbols defined by
AC_CHECK_HEADERS, AC_CHECK_FUNCS, AC_CHECK_SIZEOF,
or AC_CHECK_LIB, autoheader generates comments and
#undef statements itself rather than copying them from a file,
since the possible symbols are effectively limitless.
The file that autoheader creates contains mainly #define
and #undef statements and their accompanying comments. If
`./acconfig.h' contains the string `@TOP@',
autoheader copies the lines before the line containing
`@TOP@' into the top of the file that it generates. Similarly,
if `./acconfig.h' contains the string `@BOTTOM@',
autoheader copies the lines after that line to the end of the
file it generates. Either or both of those strings may be omitted.
An alternate way to produce the same effect is to create the files
`file.top' (typically `config.h.top') and/or
`file.bot' in the current directory. If they exist,
autoheader copies them to the beginning and end, respectively, of
its output. Their use is discouraged because they have file names that
contain two periods, and so can not be stored on MS-DOS; also, they are
two more files to clutter up the directory. But if you use the
`--localdir=dir' option to use an `acconfig.h' in another
directory, they give you a way to put custom boilerplate in each
individual `config.h.in'.
autoheader accepts the following options:
--help
-h
--localdir=dir
-l dir
--macrodir=dir
-m dir
AC_MACRODIR environment variable
to a directory; this option overrides the environment variable.
--version
In most situations, calling AC_OUTPUT is sufficient to produce
`Makefile's in subdirectories. However, configure scripts
that control more than one independent package can use
AC_CONFIG_SUBDIRS to run configure scripts for other
packages in subdirectories.
AC_OUTPUT run configure in each subdirectory
dir in the given whitespace-separated list. If a given dir
is not found, no error is reported, so a configure script can
configure whichever parts of a large source tree are present. If a
given dir contains `configure.in' but no configure,
the Cygnus configure script found by AC_CONFIG_AUXDIR is
used.
The subdirectory configure scripts are given the same
command line options that were given to this configure script,
with minor changes if needed (e.g., to adjust a relative path for the
cache file or source directory). This macro also sets the output
variable subdirs to the list of directories `dir
...'. `Makefile' rules can use this variable to determine
which subdirectories to recurse into. This macro may be called multiple
times.
By default, configure sets the prefix for files it installs to
`/usr/local'. The user of configure can select a different
prefix using the `--prefix' and `--exec-prefix' options.
There are two ways to change the default: when creating
configure, and when running it.
Some software packages might want to install in a directory besides
`/usr/local' by default. To accomplish that, use the
AC_PREFIX_DEFAULT macro.
It may be convenient for users to have configure guess the
installation prefix from the location of a related program that they
have already installed. If you wish to do that, you can call
AC_PREFIX_PROGRAM.
PATH, the way the shell does. If program
is found, set the prefix to the parent of the directory containing
program; otherwise leave the prefix specified in
`Makefile.in' unchanged. For example, if program is
gcc and the PATH contains `/usr/local/gnu/bin/gcc',
set the prefix to `/usr/local/gnu'.
configure
The following macros manage version numbers for configure
scripts. Using them is optional.
configure is earlier
than version, print an error message on the standard error output
and do not create configure. For example:
AC_PREREQ(1.8)
This macro is useful if your `configure.in' relies on non-obvious
behavior that changed between Autoconf releases. If it merely needs
recently added macros, then AC_PREREQ is less useful, because the
autoconf program already tells the user which macros are not
found. The same thing happens if `configure.in' is processed by a
version of Autoconf older than when AC_PREREQ was added.
configure
script, with any dollar signs or double-quotes removed. This macro lets
you put a revision stamp from `configure.in' into configure
without RCS or CVS changing it when you check in configure. That
way, you can determine easily which revision of `configure.in' a
particular configure corresponds to.
It is a good idea to call this macro before AC_INIT so that the
revision number is near the top of both `configure.in' and
configure. To support doing that, the AC_REVISION output
begins with `#! /bin/sh', like the normal start of a
configure script does.
For example, this line in `configure.in':
AC_REVISION($Revision: 1.30 $)dnl
produces this in configure:
#! /bin/sh # From configure.in Revision: 1.30
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.
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 that'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 -O2' for the GNU C compiler
(`-O2' on systems where GCC does not accept `-g'), or `-g'
for other compilers.
If the C compiler being used does not produce executables that can run
on the system where configure is being run, set the shell
variable cross_compiling to `yes', otherwise `no'.
In other words, this tests whether the build system type is different
from the host system type (the target system type is irrelevant to this
test). See section Manual Configuration, for more on support for cross compiling.
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,
cxx, and cc++). 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 -O2' for the GNU C++ compiler
(`-O2' on systems where G++ does not accept `-g'), or `-g'
for other compilers.
If the C++ compiler being used does not produce executables that can run
on the system where configure is being run, set the shell
variable cross_compiling to `yes', otherwise `no'.
In other words, this tests whether the build system type is different
from the host system type (the target system type is irrelevant to this
test). See section Manual Configuration, for more on support for cross compiling.
CXXCPP to a command that runs the
C++ preprocessor. If `$CXX -E' doesn't work, it uses `/lib/cpp'.
It is only portable to run CXXCPP on files with a `.c',
`.C', or `.cc' extension.
If the current language is C++ (see section Language Choice), many of the
specific test macros use the value of CXXCPP indirectly by
calling AC_TRY_CPP, AC_CHECK_HEADER,
AC_EGREP_HEADER, or AC_EGREP_CPP.
F77 is not already
set in the environment, check for g77, f77 and f2c,
in that order. Set the output variable F77 to the name of the
compiler found.
If using g77 (the GNU Fortran 77 compiler), then
AC_PROG_F77 will set the shell variable G77 to `yes',
and empty otherwise. If the output variable FFLAGS was not
already set in the environment, then set it to `-g -02' for
g77 (or `-O2' where g77 does not accept `-g').
Otherwise, set FFLAGS to `-g' for all other Fortran 77
compilers.
F77_NO_MINUS_C_MINUS_O if it
does not.
CC if using the
GNU C compiler and ioctl does not work properly without
`-traditional'. That usually happens when the fixed header files
have not been installed on an old system. Since recent versions of the
GNU C compiler fix the header files automatically when installed, this
is becoming a less prevalent problem.
INSTALL to the path of a BSD compatible
install program, if one is found in the current PATH.
Otherwise, set INSTALL to `dir/install-sh -c',
checking the directories specified to AC_CONFIG_AUX_DIR (or its
default directories) to determine dir (see section Creating Output Files). Also set
the variables INSTALL_PROGRAM and INSTALL_SCRIPT to
`${INSTALL}' and INSTALL_DATA to `${INSTALL} -m 644'.
This macro screens out various instances of install known to not
work. It prefers to find a C program rather than a shell script, for
speed. Instead of `install-sh', it can also use `install.sh',
but that name is obsolete because some make programs have a rule
that creates `install' from it if there is no `Makefile'.
A copy of `install-sh' which you may use comes with Autoconf. If
you use AC_PROG_INSTALL, you must include either
`install-sh' or `install.sh' in your distribution, or
configure will produce an error message saying it can't find
them--even if the system you're on has a good install program.
This check is a safety measure to prevent you from accidentally leaving
that file out, which would prevent your package from installing on
systems that don't have a BSD-compatible install program.
If you need to use your own installation program because it has
features not found in standard install programs, there is no
reason to use AC_PROG_INSTALL; just put the pathname of your
program into your `Makefile.in' files.
flex is found, set output variable LEX to
`flex' and LEXLIB to `-lfl', if that library is in a
standard place. Otherwise set LEX to `lex' and
LEXLIB to `-ll'.
LN_S to `ln -s', otherwise set it to `ln'.
If the link is put in a directory other than the current directory, its
meaning depends on whether `ln' or `ln -s' is used. To safely
create links using `$(LN_S)', either find out which form is used
and adjust the arguments, or always invoke ln in the directory
where the link is to be created.
In other words, it does not work to do
$(LN_S) foo /x/bar
Instead, do
(cd /x && $(LN_S) foo bar)
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)
AC_CHECK_FILE once for each file listed in files.
Additionally, defines `HAVEfile' for each file found, set to 1.
PATH. If
it is found, set variable to value-if-found, otherwise to
value-if-not-found, if given. Always pass over reject (an
absolute file name) even if it is the first found in the search path; in
that case, set variable using the absolute file name of the
prog-to-check-for found that is not reject. 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, C++ or Fortran 77 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 is
not specified, the default action will 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.
AC_TRY_LINK_FUNC first
with no libraries, then for each library listed in search-libs.
If the function is found, run action-if-found, otherwise run action-if-not-found.
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 function is present, because linking the test program will always fail with unresolved symbols.
AC_TRY_LINK_FUNC once for each
library listed in search-libs. Add `-llibrary' to
LIBS for the first library found to contain function, and
execute action-if-found. Otherwise execute
action-if-not-found.
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. */ #ifndef __GNUC__ # 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.
fnmatch function is available and works (unlike the one on
SunOS 5.4), define HAVE_FNMATCH.
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, define
HAVE_MMAP. Only checks private fixed mapping of already-mapped
memory.
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 *'.
setpgrp takes no argument (the POSIX.1 version), define
SETPGRP_VOID. Otherwise, it is the BSD version, which takes two
process ID 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.
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.
AC_CHECK_FUNCS using an action-if-not-found
that adds `function.o' to the value of the output variable
LIBOBJS. You can declare a function for which your replacement
version is used by enclosing the prototype in `#ifndef
HAVE_function'. If the system has the function, it probably
declares it in a header file you should be including, so you shouldn't
redeclare it, lest your declaration conflict.
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.
HAVE_STRINGIZE. The stringizing operator is `#' and is
found in macros such as this:
#define x(y) #y
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 Fortran 77 compiler characteristics. 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),
making sure to first set the current lanuage to Fortran 77
AC_LANG_FORTRAN77 (see section Language Choice).
FLIBS is set to these flags.
This macro is intended to be used in those situations when it is necessary to mix, e.g. C++ and Fortran 77 source code into a single program or shared library (see section `Mixing Fortran 77 With C and C++' in GNU Automake).
For example, if object files from a C++ and Fortran 77 compiler must be linked together, then the C++ compiler/linker must be used for linking (since special C++-ish things need to happen at link time like calling global constructors, instantiating templates, enabling exception support, etc.).
However, the Fortran 77 intrinsic and run-time libraries must be linked
in as well, but the C++ compiler/linker doesn't know by default how to
add these Fortran 77 libraries. Hence, the macro
AC_F77_LIBRARY_LDFLAGS was created to determine these Fortran 77
libraries.
The following macros check for operating system services or capabilities.
CYGWIN to `yes'. If not present, sets CYGWIN
to the empty string.
EXEEXT based on the output of the
compiler, after .c, .o, and .obj files have been excluded. Typically
set to empty string if Unix, `.exe' or `.EXE' if Win32.
OBJEXT based on the output of the
compiler, after .c files have been excluded. Typically
set to `.o' if Unix, `.obj' if Win32.
MINGW32 to `yes'. If not present, sets
MINGW32 to the empty string.
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.
configure.in can check
the shell variable interpval; it will be set to `yes'
if the system supports `#!', `no' if not.
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.
If the existing feature tests don't do something you need, you have to write new ones. These macros are the building blocks. They provide ways for other macros to check whether various kinds of features are available and report the results.
This chapter contains some suggestions and some of the reasons why the existing tests are written the way they are. You can also learn a lot about how to write Autoconf tests by looking at the existing ones. If something goes wrong in one or more of the Autoconf tests, this information can help you understand the assumptions behind them, which might help you figure out how to best solve the problem.
These macros check the output of the C compiler system. They do not cache the results of their tests for future use (see section Caching Results), because they don't know enough about the information they are checking for to generate a cache variable name. They also do not print any messages, for the same reason. The checks for particular kinds of C features call these macros and do cache their results and print messages about what they're checking for.
When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. See section Writing Macros, for how to do that.
The macro AC_TRY_CPP is used to check whether particular header
files exist. You can check for one at a time, or more than one if you
need several header files to all exist for some purpose.
#include statements and declarations,
on which shell variable, backquote, and backslash substitutions are
performed. (Actually, it can be any C program, but other statements are
probably not useful.) If the preprocessor produces no error messages
while processing it, run shell commands action-if-true. Otherwise
run shell commands action-if-false.
This macro uses CPPFLAGS, but not CFLAGS, because
`-g', `-O', etc. are not valid options to many C
preprocessors.
Here is how to find out whether a header file contains a particular
declaration, such as a typedef, a structure, a structure member, or a
function. Use AC_EGREP_HEADER instead of running grep
directly on the header file; on some systems the symbol might be defined
in another header file that the file you are checking `#include's.
egrep regular expression
pattern, execute shell commands action-if-found, otherwise
execute action-if-not-found.
To check for C preprocessor symbols, either defined by header files or
predefined by the C preprocessor, use AC_EGREP_CPP. Here is an
example of the latter:
AC_EGREP_CPP(yes, [#ifdef _AIX yes #endif ], is_aix=yes, is_aix=no)