Gnulib assumes that your project uses Autoconf. When using Gnulib, you will need to have Autoconf among your build tools.
Gnulib also assumes that your project’s configure.ac contains the line
The config.h file gets generated with platform dependent C macro definitions, and the source files include it (see Source changes).
Unless you use
gnulib-tool’s --gnu-make option,
Gnulib also assumes that your project uses Automake at least in a
subdirectory of your project. While the use of Automake in your
project’s top level directory is an easy way to fulfil the Makefile
conventions of the GNU coding standards, Gnulib does not require it.
Invoking ‘gnulib-tool --import’ will copy source files, create a Makefile.am to build them, generate a file gnulib-comp.m4 with Autoconf M4 macro declarations used by configure.ac, and generate a file gnulib-cache.m4 containing the cached specification of how Gnulib is used.
Our example will be a library that uses Autoconf, Automake and
Libtool. It calls
strdup, and you wish to use gnulib to make
the package portable to C99 and C11 (which don’t have
~/src/libfoo$ gnulib-tool --import strdup Module list with included dependencies: absolute-header extensions strdup string File list: lib/dummy.c lib/strdup.c lib/string.in.h m4/absolute-header.m4 m4/extensions.m4 m4/gnulib-common.m4 m4/strdup.m4 m4/string_h.m4 Creating directory ./lib Creating directory ./m4 Copying file lib/dummy.c Copying file lib/strdup.c Copying file lib/string.in.h Copying file m4/absolute-header.m4 Copying file m4/extensions.m4 Copying file m4/gnulib-common.m4 Copying file m4/gnulib-tool.m4 Copying file m4/strdup.m4 Copying file m4/string_h.m4 Creating lib/Makefile.am Creating m4/gnulib-cache.m4 Creating m4/gnulib-comp.m4 Finished. You may need to add #include directives for the following .h files. #include <string.h> Don't forget to - add "lib/Makefile" to AC_CONFIG_FILES in ./configure.ac, - mention "lib" in SUBDIRS in Makefile.am, - mention "-I m4" in ACLOCAL_AMFLAGS in Makefile.am, - invoke gl_EARLY in ./configure.ac, right after AC_PROG_CC, - invoke gl_INIT in ./configure.ac. ~/src/libfoo$
By default, the source code is copied into lib/ and the M4
macros in m4/. You can override these paths by using
modules also provide other files necessary for building. These files
are copied into the directory specified by ‘AC_CONFIG_AUX_DIR’ in
configure.ac or by the
--aux-dir=DIRECTORY option. If
neither is specified, the current directory is assumed.
gnulib-tool can make symbolic links instead of copying the
source files. The option to specify for this is ‘--symlink’, or
‘-s’ for short. This can be useful to save a few kilobytes of disk
space. But it is likely to introduce bugs when
gnulib is updated;
it is more reliable to use ‘gnulib-tool --update’ (see below)
to update to newer versions of
gnulib. Furthermore it requires
extra effort to create self-contained tarballs, and it may disturb some
mechanism the maintainer applies to the sources. For these reasons,
this option is generally discouraged.
gnulib-tool will overwrite any pre-existing files, in
particular Makefile.am. It is also possible to separate the
generated Makefile.am content (for building the gnulib library)
into a separate file, say gnulib.mk, that can be included by your
handwritten Makefile.am, but this is a more advanced use of
Consequently, it is a good idea to choose directories that are not
already used by your projects, to separate gnulib imported files from
your own files. This approach is also useful if you want to avoid
conflicts between other tools (e.g.,
gettextize that also copy
M4 files into your package. Simon Josefsson successfully uses a source
base of gl/, and a M4 base of gl/m4/, in several
After the ‘--import’ option on the command line comes the list of Gnulib modules that you want to incorporate in your package. The names of the modules coincide with the filenames in Gnulib’s modules/ directory.
Some Gnulib modules depend on other Gnulib modules.
will automatically add the needed modules as well; you need not list
gnulib-tool will also memorize which dependent
modules it has added, so that when someday a dependency is dropped, the
implicitly added module is dropped as well (unless you have explicitly
requested that module).
If you want to cut a dependency, i.e., not add a module although one of your requested modules depends on it, you may use the option ‘--avoid=module’ to do so. Multiple uses of this option are possible. Of course, you will then need to implement the same interface as the removed module.
A few manual steps are required to finish the initial import.
gnulib-tool printed a summary of these steps.
First, you must ensure Autoconf can find the macro definitions in
gnulib-comp.m4. Use the
ACLOCAL_AMFLAGS specifier in
your top-level Makefile.am file, as in:
ACLOCAL_AMFLAGS = -I m4
You are now ready to call the M4 macros in
configure.ac. The macro
gl_EARLY must be called as soon
as possible after verifying that the C compiler is working.
Typically, this is immediately after
AC_PROG_CC, as in:
... AC_PROG_CC gl_EARLY ...
If you are using
AC_PROG_CC_STDC, the macro
be called after it, like this:
... AC_PROG_CC AC_PROG_CC_STDC gl_EARLY ...
The core part of the gnulib checks are done by the macro
gl_INIT. Place it further down in the file, typically where
you normally check for header files or functions. It must come after
other checks which may affect the compiler invocation, such as
AC_MINIX. For example:
... # For gnulib. gl_INIT ...
gl_INIT will in turn call the macros related with the
gnulib functions, be it specific gnulib macros, like
or Autoconf or Automake macros like
AM_FUNC_GETLINE. So there is no need to call those macros yourself
when you use the corresponding gnulib modules.
You must also make sure that the gnulib library is built. Add the
Makefile in the gnulib source base directory to
AC_CONFIG_FILES, as in:
AC_CONFIG_FILES(... lib/Makefile ...)
You must also make sure that
make will recurse into the gnulib
directory. To achieve this, add the gnulib source base directory to a
SUBDIRS Makefile.am statement, as in:
SUBDIRS = lib
or if you, more likely, already have a few entries in
you can add something like:
SUBDIRS += lib
Finally, you have to add compiler and linker flags in the appropriate source directories, so that you can make use of the gnulib library. Since some modules (‘getopt’, for example) may copy files into the build directory, top_builddir/lib is needed as well as top_srcdir/lib. For example:
... AM_CPPFLAGS = -I$(top_builddir)/lib -I$(top_srcdir)/lib ... LDADD = lib/libgnu.a ...
Don’t forget to
#include the various header files. In this
example, you would need to make sure that ‘#include <string.h>’
is evaluated when compiling all source code files, that want to make
In the usual case where Autoconf is creating a config.h file, you should include config.h first, before any other include file. That way, for example, if config.h defines ‘restrict’ to be the empty string on a non-C99 host, or a macro like ‘_FILE_OFFSET_BITS’ that affects the layout of data structures, the definition is consistent for all include files. Also, on some platforms macros like ‘_FILE_OFFSET_BITS’ and ‘_GNU_SOURCE’ may be ineffective, or may have only a limited effect, if defined after the first system header file is included.
Finally, note that you cannot use
AC_REPLACE_FUNCS in your configure.ac and expect the
resulting object files to be automatically added to lib/libgnu.a.
This is because your
from configure.ac augment a variable
@LTLIBOBJS@ if using Libtool), whereas lib/libgnu.a
is built from the contents of a different variable, usually
@gl_LTLIBOBJS@ if using Libtool).