I have problems mixing Fortran and C code, why?

A few routines (such as getenv, signal, and system) exist in both the
Fortran and C libraries but with different parameters. In the recent
past, if you have a mixed program that calls getenv from both C and
Fortran code, you have to link them carefully by specifying the correct
library first on your command line. This is no longer needed starting
with version 1.5 of the compilers.