7.2 Libraries

Building a library is much like building a program. In this case, the name of the primary is LIBRARIES. Libraries can be installed in libdir or pkglibdir.

See Shared libraries for information on how to build shared libraries using libtool and the LTLIBRARIES primary.

Each _LIBRARIES variable is a list of the libraries to be built. For instance, to create a library named libcpio.a, but not install it, you would write:

noinst_LIBRARIES = libcpio.a
libcpio_a_SOURCES = …

The sources that go into a library are determined exactly as they are for programs, via the _SOURCES variables. Note that the library name is canonicalized (see Other Automake variables), so the _SOURCES variable corresponding to libcpio.a is ‘libcpio_a_SOURCES’, not ‘libcpio.a_SOURCES’.

Extra objects can be added to a library using the library_LIBADD variable. This should be used for objects determined by configure. Again from cpio:

libcpio_a_LIBADD = $(LIBOBJS) $(ALLOCA)

In addition, sources for extra objects that will not exist until configure-time must be added to the BUILT_SOURCES variable (see Sources).

Building a static library is done by compiling all object files, then by invoking ‘$(AR) $(ARFLAGS)’ followed by the name of the library and the list of objects, and finally by calling ‘$(RANLIB)’ on that library. You should call AC_PROG_RANLIB from your configure.ac to define RANLIB (Automake will complain otherwise). You should also call AM_PROG_AR to define AR, in order to support unusual archivers such as Microsoft lib. ARFLAGS will default to cru; you can override this variable by setting it in your Makefile.am or by AC_SUBSTing it from your configure.ac. You can override the AR variable by defining a per-library library_AR variable (see Program and Library Variables).

Be careful when selecting library components conditionally. Because building an empty library is not portable, you should ensure that any library always contains at least one object.

To use a static library when building a program, add it to LDADD for this program. In the following example, the program cpio is statically linked with the library libcpio.a.

noinst_LIBRARIES = libcpio.a
libcpio_a_SOURCES = …

bin_PROGRAMS = cpio
cpio_SOURCES = cpio.c …
cpio_LDADD = libcpio.a