LinuxQuestions.org - autoconf qns

About a year ago I was wondering exactly the same things. I didn't find autoconf/automake/m4 stuff very easy. When I read your question I decided to make very basic example package that does the things you asked, so I have it documented for myself in the future as well.

Get it here if you are interested:
http://www.xs4all.nl/~heiky/myprog-0.1.tar.gz

It boils down to this:

Quote:

1. How do I define a custom #define macro in config.h based on configure arguments? eg if I set --with-foo, I would like to have #define WITH_FOO 1 set in config.h

In your package source directory create a file "ac_foo.m4" that looks like this:
(this assumes --with-foo to specify a library directory, not "WITH_FOO 1", but you can figure out how to that from this. It will be easier I think)

Code:

AC_DEFUN([AC_FOO], [

        AC_ARG_WITH([foo], AC_HELP_STRING([--with-foo=DIR], [Foo directory.]), [foo_dir=$withval])



        dnl Do shell scripting here in most cross-platform

        dnl compatible bourne shell (sh) code



        dnl First make sure there's a default for the foo directory ($foo_dir)

        dnl (if --with-foo is not given, m4 parameter here will be empty)

        if test "x$foo_dir" = "x"

        then

                foo_dir=/usr/local/lib/foo

        fi



        dnl Make configure print a "Checking for..." message.

        AC_MSG_CHECKING([for Foo library files])



        dnl Find the directory of foo and check to see

        dnl if $foo_dir contains what you expect from it.

        if ! test -f $foo_dir/foo.so

        then

                dnl This will exit the configure script

                AC_MSG_FAILURE(["Foo library not found!])

        fi



        dnl If did not exit before this line the foo lib dir is OK.



        dnl Set CFLAGS according to what directory we have found

        CFLAGS="$CFLAGS -L$foo_dir"



        dnl Have configure say that it's OK

        AC_MSG_RESULT([yes])



])

Also create a file called "acinclude.m4" to make the above file known to autoconf. This file should look like this:

Code:

sinclude(ac_foo.m4)

And, to make sure "make dist" and "make distcheck" will package the new files in the distribution make sure this is in your "Makefile.am":

Code:

EXTRA_DIST = ac_foo.m4

And finally call the new m4 macro (from the file "ac_foo.m4") from "configure.ac":

Code:

AC_INIT([My Program], [0.1], [you@somewhere.com], [myprog])

AC_CONFIG_SRCDIR([main.c])

AM_INIT_AUTOMAKE

AC_CONFIG_HEADERS([config.h])

AC_PROG_CC

AC_PROG_INSTALL

AC_FOO

AC_CONFIG_FILES([Makefile])

AC_OUTPUT

Quote:

2. How do I make the directory variables (eg @includedir, @shareddir etc) visible to my code? I know how to achieve this by adding -D options to AM_CPPFLAGS in Makefile.am, but I would like to have the macros inside config.h. Can this be done?

I found an m4 file that does this in the "autoconf archive" from the GNU site. It's called "ac_define_dir:

Code:

dnl Taken from the autoconf archive (www.gnu.org)

dnl

dnl @synopsis AC_DEFINE_DIR(VARNAME, DIR [, DESCRIPTION])

dnl

dnl This macro _AC_DEFINEs VARNAME to the expansion of the DIR

dnl variable, taking care of fixing up ${prefix} and such.

dnl

dnl Note that the 3 argument form is only supported with autoconf 2.13 and

dnl later (i.e. only where _AC_DEFINE supports 3 arguments).

dnl

dnl Examples:

dnl

dnl    AC_DEFINE_DIR(DATADIR, datadir)

dnl    AC_DEFINE_DIR(PROG_PATH, bindir, [Location of installed binaries])

dnl

dnl @version $Id: ac_define_dir.m4,v 1.1 2002/12/31 02:15:21 heiko Exp $

dnl @author Guido Draheim <guidod@gmx.de>, original by Alexandre Oliva



AC_DEFUN([AC_DEFINE_DIR], [

  test "x$prefix" = xNONE && prefix="$ac_default_prefix"

  test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'

  ac_define_dir=`eval echo [$]$2`

  ac_define_dir=`eval echo [$]ac_define_dir`

  ifelse($3, ,

    AC_DEFINE_UNQUOTED($1, "$ac_define_dir"),

    AC_DEFINE_UNQUOTED($1, "$ac_define_dir", $3))

])

To use this, put this file also in your source directory, and like the --with-foo procedure above, mention it in the "acinclude.m4" file:

Code:

sinclude(ac_foo.m4)

sinclude(ac_define_dir.m4)

..and in your Makefile.am:

Code:

EXTRA_DIST = ac_define_dir.m4 ac_foo.m4

(note that the "ac_foo.m4" stuff from before is also included)

And finally call it from configure.ac". Here the datadir is #defined in config.h. (the datadir is the directory to store data used by your program. By default ./configure will make it: $PREFIX/share)

Code:

AC_DEFINE_DIR([DATADIR], [datadir], [Directory for data files.])

Quote:

3. How do I fail the configure script when a test fails. eg if AC_HEADER_STDC is not found, exit/fail the configure script.

Use this (also see the first listing in this post):

Code:

AC_MSG_FAILURE(["Your custom error message"])

Like I already said, I've put a working example program package including all this on the web at:
http://www.xs4all.nl/~heiky/myprog-0.1.tar.gz

If you can improve or extend that, I'd be very interested!