How do I compile a C program that links against a library written in FORTRAN?

From DANSE

In your local.def file, add

PROJ_LIBRARIES += $(COMPILER_LCXX_FORTRAN)

for C++, and

PROJ_LIBRARIES += $(COMPILER_LCC_FORTRAN)

for C. This will add libraries such as libg2c.a (to use gcc as an example) that supply standard FORTRAN functions. Of course if you're using a different compiler, that compiler will define COMPILER_LCC_FORTRAN to the correct libararies.