8.2 Building a library

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 section Building a Shared Library, 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 section How derived variables are named), 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 section Built 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). AR and ARFLAGS default to ar and cru respectively; you can override these two variables my setting them in your ‘Makefile.am’, by AC_SUBSTing them from your ‘configure.ac’, or by defining a per-library maude_AR variable (see section 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