Autoconf Macro Reference

This is an alphabetical list of each Autoconf macro used in this book, along with a description of what each does.
The documents is not made by me. I just extract it from the e-book written by Gary V. Vaughan.

AC_ARG_ENABLE(feature, help-text, [if-given], [if-not-given])
This macro allows the maintainer to specify additional package options
accepted by `configure'–for example, `–enable-zlib’. The
action shell code may access any arguments to the option in the shell
variable enableval. For example, `–enable-buffers=128′
would cause `configure' to set enableval to `128′.

This macro places a sed transformation program into the output
variable program_transform_name that can be used to transform the
filenames of installed programs. If the `–program-prefix’,
`–program-suffix’ or
`–program-transform-name’ options
are passed to `configure', an appropriate transformation program
will be generated. If no options are given, but the type of the host
system differs from the type of the target system, program names are
transformed by prefixing them with the type of the target
(eg. arm-elf-gcc).

AC_ARG_WITH(package, help-text, [if-given], [if-not-given])
This macro allows the maintainer to specify additional packages that
this package should work with (for example, a library to manipulate
shadow passwords). The user indicates this preference by invoking
`configure' with an option such as `–with-shadow’. If an
optional argument is given, this value is available to shell code in the
shell variable withval.

AC_CACHE_CHECK(message, cache-variable, commands)
This macro is a convenient front-end to the AC_CACHE_VAL macro
that takes care of printing messages to the user, including whether or
not the result was found in the cache. It should be used in preference

AC_CACHE_VAL(cache-variable, commands)
This is a low-level macro which implements the Autoconf cache feature.
If the named variable is set at runtime (for instance, if it was read
from `config.cache'), then this macro does nothing. Otherwise, it
runs the shell code in commands, which is assumed to set the cache

This macro determines the type of the host system and sets the output
variable `host’, as well as other more obscure variables.

This macro determines the type of the build, host and target systems and
sets the output variables `build’, `host’ and `target’,
amongst other more obscure variables.

AC_CHECK_FILE(file, [if-found], [if-not-found])
This macro tests for the existence of a file in the file system of the
build system, and runs the appropriate shell code depending on whether
or not the file is found.

AC_CHECK_FUNCS(function-list, [if-found], [if-not-found])
This looks for a series of functions. If the function quux is
found, the C preprocessor macro HAVE_QUUX will be defined. In
addition, if the if-found argument is given, it will be run (as
shell code) when a function is found — this code can use the sh
break command to prevent AC_CHECK_FUNCS from looking for
the remaining functions in the list. The shell code in
if-not-found is run if a function is not found.

AC_CHECK_HEADER(header, [if-found], [if-not-found])
This macro executes some specified shell code if a header file exists.
If it is not present, alternative shell code is executed instead.

AC_CHECK_HEADERS(header-list, [if-found], [if-not-found])
This looks for a series of headers. If the header quux.h is
found, the C preprocessor macro HAVE_QUUX_H will be defined. In
addition, if the if-found argument is given, it will be run (as
shell code) when a header is found — this code can use the sh
break command to prevent AC_CHECK_HEADERS from looking for
the remaining headers in the list. The shell code in if-not-found
is run if a header is not found.

AC_CHECK_LIB(library, function, [if-found], [if-not-found], [other-libraries])
This looks for the named function in the named library specified by its
base name. For instance the math library, `libm.a', would be named
simply `m’. If the function is found in the library `foo’,
then the C preprocessor macro HAVE_LIBFOO is defined.

AC_CHECK_PROG(variable, program-name, value-if-found, [value-if-not-found], [path], [reject])
Checks to see if the program named by program-name exists in the
path path. If found, it sets the shell variable variable to
the value value-if-found; if not it uses the value
value-if-not-found. If variable is already set at runtime,
this macro does nothing.

AC_CHECK_SIZEOF(type, [size-if-cross-compiling])
This macro determines the size of C and C++ built-in types and defines
SIZEOF_type to the size, where type is transformed–all
characters to upper case, spaces to underscores and `*’ to
`P’. If the type is unknown to the compiler, the size is set to 0.
An optional argument specifies a default size when cross-compiling. The
`configure' script will abort with an error message if it tries to
cross-compile without this default size.

This macro allows an alternative directory to be specified for the
location of auxiliary scripts such as `config.guess',
`config.sub' and `install-sh'. By default, `$srcdir',
`$srcdir/..' and `$srcdir/../..' are searched for these files.

This indicates that you want to use a config header, as opposed to
having all the C preprocessor macros defined via -D options in
the DEFS `Makefile' variable. Each header named in
header-list is created at runtime by `configure' (via
AC_OUTPUT). There are a variety of optional features for use
with config headers (different naming schemes and so forth); see the
reference manual for more information.

This macro defines the C preprocessor macro const to the string
const if the C compiler supports the const keyword.
Otherwise it is defined to be the empty string.

This macro tests if the C compiler can accept the inline keyword.
It defines the C preprocessor macro inline to be the keyword
accepted by the compiler or the empty string if it is not accepted at

AC_DEFINE(variable, [value], [description])
This is used to define C preprocessor macros. The first argument is the
name of the macro to define. The value argument, if given, is the
value of the macro. The final argument can be used to avoid adding an
`#undef’ for the macro to `acconfig.h'.

AC_DEFINE_UNQUOTED(variable, [value], [description])
This is like AC_DEFINE, but it handles the quoting of value
differently. This macro is used when you want to compute the value
instead of having it used verbatim.

AC_DEFUN(name, body)
This macro is used to define new macros. It is similar to M4’s
define macro, except that it performs additional internal

This macro can be used to disable Libtool’s `fast install’ feature.

This macro changes the default behavior of AC_PROG_LIBTOOL so
that shared libraries will not be built by default. The user can still
override this new default by using `–enable-shared’.

This macro changes the default behavior of AC_PROG_LIBTOOL so
that static libraries will not be built by default. The user can still
override this new default by using `–enable-static’.

Sets the output variable EXEEXT to the extension of executables
produced by the compiler. It is usually set to the empty string on Unix
systems and `.exe’ on Windows.

This macro defines the C preprocessor macro HAVE_ALLOCA if the
various tests indicate that the C compiler has built-in alloca
support. If there is an `alloca.h' header file, this macro defines
HAVE_ALLOCA_H. If, instead, the alloca function is found
in the standard C library, this macro defines C_ALLOCA and sets
the output variable ALLOCA to alloca.o.

This macro tests if the getpgrp function takes a process ID as an
argument or not. If it does not, the C preprocessor macro
GETPGRP_VOID is defined.

This macro tests for a working version of the memcmp function.
If absent, or it does not work correctly, `memcmp.o' is added to
the LIBOBJS output variable.

Defines the C preprocessor macro HAVE_MMAP if the mmap
function exists and works.

On some systems, the order of the mode and buf arguments
is reversed with respect to the ANSI C standard. If so, this macro
defines the C preprocessor macro SETVBUF_REVERSED.

Defines the C preprocessor macro HAVE_UTIME_NULL if a call to
utime with a NULL utimbuf pointer sets the file’s
timestamp to the current time.

Defines the C preprocessor macro HAVE_VPRINTF if the
vprintf function is available. If not and the _doprnt
function is available instead, this macro defines HAVE_DOPRNT.

This macro searches a number of specific header files for a declaration
of the C type DIR. Depending on which header file the
declaration is found in, this macro may define one of the C preprocessor
HAVE_SYS_DIR_H or HAVE_NDIR_H. Refer to the Autoconf
manual for an example of how these macros should be used in your source

This macro defines the C preprocessor macro STDC_HEADERS if the
system has the ANSI standard C header files. It determines this by
testing for the existence of the `stdlib.h', `stdarg.h',
`string.h' and `float.h' header files and testing if
`string.h' declares memchr, `stdlib.h' declares
free, and `ctype.h' macros such as isdigit work with
8-bit characters.

This macro performs essential initialization for the generated
`configure' script. An optional argument may provide the name of a
file from the source directory to ensure that the directory has been
specified correctly.

Call this macro before AC_PROG_LIBTOOL to indicate that your
package wants to use Libtool’s support for dlopened modules.

Call this macro before AC_PROG_LIBTOOL to indicate that your
package has been written to build DLLs on Windows. If this macro
is not called, Libtool will only build static libraries on Windows.

This macro does the configure-time checks needed to cause
`ltdl.c' to be compiled correctly. That is, this is used to enable
dynamic loading via libltdl.

AC_LINK_FILES(source-list, dest-list)
Use this macro to create a set of links; if possible, symlinks are made.
The two arguments are parallel lists: the first element of
dest-list is the name of a to-be-created link whose target is the
first element of source-list.

This macro outputs a message to the user in the usual style of
`configure' scripts: leading with the word `checking’ and
ending in `…’. This message gives the user an indication that
the `configure' script is still working. A subsequent invocation
of AC_MSG_RESULT should be used to output the result of a test.

This macro outputs an error message to standard error and aborts the
`configure' script. It should only be used for fatal error

This macro should be invoked after a corresponding invocation of
AC_MSG_CHECKING with the result of a test. Often the result
string can be as simple as `yes’ or `no’.

This macro outputs a warning to standard error, but allows the
`configure' script to continue. It should be used to notify the
user of abnormal, but non-fatal, conditions.

Sets the output variable OBJEXT to the extension of object files
produced by the compiler. Usually, it is set to `.o’ on Unix
systems and `.obj’ on Windows.

AC_OUTPUT(files, [extra-commands], [init-commands])
This macro must be called at the end of every `'. It
creates each file listed in files. For a given file, by default,
configure reads the template file whose name is the name of the
input file with `.in’ appended — for instance, `Makefile' is
generated from `'. This default can be overridden by
using a special naming convention for the file.

For each name `foo’ given as an argument to AC_SUBST,
configure will replace any occurrence of `@foo@’ in the
template file with the value of the shell variable `foo’ in the
generated file. This macro also generates the config header, if
AC_CONFIG_HEADER was called, and any links, if
AC_LINK_FILES was called. The additional arguments can be used
to further tailor the output processing.

AC_OUTPUT_COMMANDS(extra-commands, [init-commands])
This macro works like the optional final arguments of AC_OUTPUT,
except that it can be called more than once from `'.
(This makes it possible for macros to use this feature and yet remain
modular.) See the reference manual for the precise definition of this

This macro searches for an awk program and sets the output
variable AWK to be the best one it finds.

This checks for the C compiler to use and sets the shell variable
CC to the value. If the GNU C compiler is being used, this
sets the shell variable GCC to `yes’. This macro sets the
shell variable CFLAGS if it has not already been set. It also
calls AC_SUBST on CC and CFLAGS.

This macro attempts to discover a necessary command line option to have
the C compiler accept ANSI C. If so, it adds the option to the
CC. If it were not possible to get the C compiler to accept
ANSI, the shell variable ac_cv_prog_cc_stdc will be set to

This macro sets the output variable CPP to a command that runs
the C preprocessor. If `$CC -E’ does not work, it will set the
variable to `/lib/cpp'.

This is like AC_PROG_CC, but it checks for the C++ compiler, and
sets the variables CXX, GXX and CXXFLAGS.

This macro determines if GCC requires the `-traditional’
option in order to compile code that uses ioctl and, if so, adds
`-traditional’ to the CC output variable. This condition is
rarely encountered, thought mostly on old systems.

This looks for an install program and sets the output variables
INSTALL_SCRIPT. This macro assumes that if an install
program cannot be found on the system, your package will have
`install-sh' available in the directory chosen by

This looks for a lex-like program and sets the `Makefile'
variable LEX to the result. It also sets LEXLIB to
whatever might be needed to link against lex output.

This macro is the primary way to integrate Libtool support into
`configure'. If you are using Libtool, you should call this macro
in `'. Among other things, it adds support for the
`–enable-shared’ configure flag.

This sets the `Makefile' variable LN_S to `ln -s’ if
symbolic links work in the current working directory. Otherwise it sets
LN_S to just `ln’.

Some versions of make need to have the `Makefile' variable
MAKE set in `Makefile' in order for recursive builds to
work. This macro checks whether this is needed, and, if so, it sets the
`Makefile' variable SET_MAKE to the result.
AM_INIT_AUTOMAKE calls this macro, so if you are using Automake,
you don’t need to call it or use SET_MAKE in `'.

This searches for the ranlib program. It sets the
`Makefile' variable RANLIB to the result. If ranlib is
not found, or not needed on the system, then the result is :.

This searches for the yacc program — it tries bison,
byacc, and yacc. It sets the `Makefile' variable
YACC to the result.

AC_REPLACE_FUNCS(function list)
This macro takes a single argument, which is a list of functions. For a
given function `func’, `configure' will do a link test to try
to find it. If the function cannot be found, then `func.o’ will be
added to LIBOBJS. If function can be found, then
`configure' will define the C preprocessor symbol HAVE_FUNC.

This macro takes a single argument, which is the name of another macro.
(Note that you must quote the argument correctly:
AC_REQUIRE([FOO]) is correct, while AC_REQUIRE(FOO) is
not.) If the named macro has already been invoked, then
AC_REQUIRE does nothing. Otherwise, it invokes the named macro
with no arguments.

This macro takes a single argument, a version string. Autoconf will
copy this string into the generated `configure' file.

Defines the C preprocessor macro HAVE_ST_BLKSIZE if struct
has an st_blksize member.

Defines the C preprocessor macro HAVE_ST_BLOCKS if struct
has an st_blocks member.

Defines the C preprocessor macro HAVE_ST_RDEV if struct
has an st_rdev member.

This macro looks for struct tm in `time.h' and defines
TM_IN_SYS_TIME if it is not found there.

This macro takes a single argument, which is the name of a shell
variable. When configure generates the files listed in
AC_OUTPUT (e.g., `Makefile'), it will substitute the
variable’s value (at the end of the configure run — the value
can be changed after AC_SUBST is called) anywhere a string of the
form `@name@’ is seen.

AC_TRY_COMPILE(includes, body, [if-ok], [if-not-ok])
This macro is used to try to compile a given function, whose body is
given in body. includes lists any `#include’
statements needed to compile the function. If the code compiles
correctly, the shell commands in if-ok are run; if not,
if-not-ok is run. Note that this macro will not try to link the
test program — it will only try to compile it.

AC_TRY_LINK(includes, body, [if-found], [if-not-found])
This is used like AC_TRY_COMPILE, but it tries to link the
resulting program. The libraries and options in the LIBS shell
variable are passed to the link.

AC_TRY_RUN(program, [if-true, [if-false], [if-cross-compiling])
This macro tries to compile and link the program whose text is in
program. If the program compiles, links, and runs successfully,
the shell code if-true is run. Otherwise, the shell code
if-false is run. If the current configure is a cross-configure,
then the program is not run, and on a successful compile and link, the
shell code if-cross-compiling is run.

This macro defines the C preprocessor macro RETSIGTYPE to be the
correct return type of signal handlers. For instance, it might be
`void’ or `int’.

This macro looks for the type size_t. If not defined on the
system, it defines it (as a macro) to be `unsigned’.

AM_CONDITIONAL(name, testcode)
This Automake macro takes two arguments: the name of a conditional and a
shell statement that is used to determine whether the conditional should
be true or false. If the shell code returns a successful (0) status,
then the conditional will be true. Any conditional in your
`' is automatically available for use in any
`' in that project.

This is just like AC_CONFIG_HEADER, but does some additional
setup required by Automake. If you are using Automake, use this macro.
Otherwise, use AC_CONFIG_HEADER.

AM_INIT_AUTOMAKE(package, version, [nodefine])
This macro is used to do all the standard initialization required by
Automake. It has two required arguments: the package name and the
version number. This macro sets and calls AC_SUBST on the shell
variables PACKAGE and VERSION. By default it also defines
these variables (via AC_DEFINE_UNQUOTED). However, this macro
also accepts an optional third argument which, if not empty, means that
VERSION should be suppressed.

This macro is used to enable a special Automake feature, maintainer
mode, which we’ve documented elsewhere.

This macro takes no arguments. It is used to try to get the C compiler
to be ANSI compatible. It does this by adding different options
known to work with various system compilers. This macro is most
typically used in conjunction with Automake when you want to use the
automatic de-ANSI-fication feature.

This is like AC_PROG_LEX, but it does some additional processing
used by Automake-generated `Makefile's. If you are using Automake,
then you should use this. Otherwise, you should use AC_PROG_LEX
(and perhaps AC_DECL_YYTEXT, which AM_PROG_LEX calls).

This macro adds support for the `–with-dmalloc’ flag to
configure. If the user chooses to enable dmalloc support,
then this macro will define the preprocessor symbol `WITH_DMALLOC’
and will add `-ldmalloc’ to the `Makefile' variable

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