10.12.4 Mixing Fortran 77 With C and C++

Automake currently provides limited support for creating programs and shared libraries that are a mixture of Fortran 77 and C and/or C++. However, there are many other issues related to mixing Fortran 77 with other languages that are not (currently) handled by Automake, but that are handled by other packages⁸.

Automake can help in two ways:

1. Automatic selection of the linker depending on which combinations of source code.
2. Automatic selection of the appropriate linker flags (e.g., -L and -l) to pass to the automatically selected linker in order to link in the appropriate Fortran 77 intrinsic and run-time libraries.

   These extra Fortran 77 linker flags are supplied in the output variable FLIBS by the AC_F77_LIBRARY_LDFLAGS Autoconf macro. See Fortran Compiler.

If Automake detects that a program or shared library (as mentioned in some _PROGRAMS or _LTLIBRARIES primary) contains source code that is a mixture of Fortran 77 and C and/or C++, then it requires that the macro AC_F77_LIBRARY_LDFLAGS be called in configure.ac, and that either $(FLIBS) appear in the appropriate _LDADD (for programs) or _LIBADD (for shared libraries) variables. It is the responsibility of the person writing the Makefile.am to make sure that ‘$(FLIBS)’ appears in the appropriate _LDADD or _LIBADD variable.

For example, consider the following Makefile.am:

bin_PROGRAMS = foo
foo_SOURCES  = main.cc foo.f
foo_LDADD    = libfoo.la $(FLIBS)

pkglib_LTLIBRARIES = libfoo.la
libfoo_la_SOURCES  = bar.f baz.c zardoz.cc
libfoo_la_LIBADD   = $(FLIBS)

In this case, Automake will insist that AC_F77_LIBRARY_LDFLAGS is mentioned in configure.ac. Also, if ‘$(FLIBS)’ hadn’t been mentioned in foo_LDADD and libfoo_la_LIBADD, then Automake would have issued a warning.