2.10 Options for interoperability with other languages

-fc-prototypes

This option will generate C prototypes from BIND(C) variable declarations, types and procedure interfaces and writes them to standard output. ENUM is not yet supported.

The generated prototypes may need inclusion of an appropriate header, such as <stdint.h> or <stdlib.h>. For types which are not specified using the appropriate kind from the iso_c_binding module, a warning is added as a comment to the code.

For function pointers, a pointer to a function returning int without an explicit argument list is generated.

Example of use:

$ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h

where the C code intended for interoperating with the Fortran code then uses #include "foo.h".

-fc-prototypes-external

This option will generate C prototypes from external functions and subroutines and write them to standard output. This may be useful for making sure that C bindings to Fortran code are correct. This option does not generate prototypes for BIND(C) procedures, use -fc-prototypes for that.

The generated prototypes may need inclusion of an appropriate header, such as as <stdint.h> or <stdlib.h>.

This is primarily meant for legacy code to ensure that existing C bindings match what gfortran emits. The generated C prototypes should be correct for the current version of the compiler, but may not match what other compilers or earlier versions of gfortran need. For new developments, use of the BIND(C) features is recommended.

Example of use:

$ gfortran -fc-prototypes-external -fsyntax-only foo.f > foo.h

where the C code intended for interoperating with the Fortran code then uses #include "foo.h".