15.4 Autoconf macro

GNU Gnulib provides an autoconf macro that tests for the availability of libunistring. It is contained in the Gnulib module ‘libunistring’, see http://www.gnu.org/software/gnulib/MODULES.html#module=libunistring.

The macro is called gl_LIBUNISTRING. It searches for an installed libunistring. If found, it sets and AC_SUBSTs HAVE_LIBUNISTRING=yes and the LIBUNISTRING and LTLIBUNISTRING variables and augments the CPPFLAGS variable, and defines the C macro HAVE_LIBUNISTRING to 1. Otherwise, it sets and AC_SUBSTs HAVE_LIBUNISTRING=no and LIBUNISTRING and LTLIBUNISTRING to empty.

The complexities that gl_LIBUNISTRING deals with are the following:

• On some operating systems, in some configurations, libunistring depends on libiconv, and the options for linking with libiconv must be mentioned explicitly on the link command line.
• GNU libunistring, if installed, is not necessarily already in the search path (CPPFLAGS for the include file search path, LDFLAGS for the library search path).
• GNU libunistring, if installed, is not necessarily already in the run time library search path. To avoid the need for setting an environment variable like LD_LIBRARY_PATH, the macro adds the appropriate run time search path options to the LIBUNISTRING variable. This works on most systems.