# FortranCInterface

Fortran/C Interface Detection

This module automatically detects the API by which C and Fortran languages interact. Variables indicate if the mangling is found:

    FortranCInterface_GLOBAL_FOUND = Global subroutines and functions
    FortranCInterface_MODULE_FOUND = Module subroutines and functions
                                     (declared by "MODULE PROCEDURE")

A function is provided to generate a C header file containing macros to mangle symbol names:

    FortranCInterface_HEADER(<file>
                             [MACRO_NAMESPACE <macro-ns>]
                             [SYMBOL_NAMESPACE <ns>]
                             [SYMBOLS [<module>:]<function> ...])

It generates in <file> definitions of the following macros:

    #define FortranCInterface_GLOBAL (name,NAME) ...
    #define FortranCInterface_GLOBAL_(name,NAME) ...
    #define FortranCInterface_MODULE (mod,name, MOD,NAME) ...
    #define FortranCInterface_MODULE_(mod,name, MOD,NAME) ...

These macros mangle four categories of Fortran symbols, respectively:

    - Global symbols without '_': call mysub()
    - Global symbols with '_'   : call my_sub()
    - Module symbols without '_': use mymod; call mysub()
    - Module symbols with '_'   : use mymod; call my_sub()

If mangling for a category is not known, its macro is left undefined. All macros require raw names in both lower case and upper case. The MACRO_NAMESPACE option replaces the default “FortranCInterface” prefix with a given namespace “<macro-ns>”.

The SYMBOLS option lists symbols to mangle automatically with C preprocessor definitions:

    <function>          ==> #define <ns><function> ...
    <module>:<function> ==> #define <ns><module>_<function> ...

If the mangling for some symbol is not known then no preprocessor definition is created, and a warning is displayed. The SYMBOL_NAMESPACE option prefixes all preprocessor definitions generated by the SYMBOLS option with a given namespace “<ns>”.

Example usage:

    include(FortranCInterface)
    FortranCInterface_HEADER(FC.h MACRO_NAMESPACE "FC_")

This creates a “FC.h” header that defines mangling macros FC_GLOBAL(), FC_GLOBAL_(), FC_MODULE(), and FC_MODULE_().

Example usage:

    include(FortranCInterface)
    FortranCInterface_HEADER(FCMangle.h
                             MACRO_NAMESPACE "FC_"
                             SYMBOL_NAMESPACE "FC_"
                             SYMBOLS mysub mymod:my_sub)

This creates a “FCMangle.h” header that defines the same FC_*() mangling macros as the previous example plus preprocessor symbols FC_mysub and FC_mymod_my_sub.

Another function is provided to verify that the Fortran and C/C++ compilers work together:

    FortranCInterface_VERIFY([CXX] [QUIET])

It tests whether a simple test executable using Fortran and C (and C++ when the CXX option is given) compiles and links successfully. The result is stored in the cache entry FortranCInterface_VERIFIED_C (or FortranCInterface_VERIFIED_CXX if CXX is given) as a boolean. If the check fails and QUIET is not given the function terminates with a FATAL_ERROR message describing the problem. The purpose of this check is to stop a build early for incompatible compiler combinations. The test is built in the Release configuration.

FortranCInterface is aware of possible GLOBAL and MODULE manglings for many Fortran compilers, but it also provides an interface to specify new possible manglings. Set the variables

    FortranCInterface_GLOBAL_SYMBOLS
    FortranCInterface_MODULE_SYMBOLS

before including FortranCInterface to specify manglings of the symbols “MySub”, “My_Sub”, “MyModule:MySub”, and “My_Module:My_Sub”. For example, the code:

    set(FortranCInterface_GLOBAL_SYMBOLS mysub_ my_sub__ MYSUB_)
      #                                  ^^^^^  ^^^^^^   ^^^^^
    set(FortranCInterface_MODULE_SYMBOLS
        __mymodule_MOD_mysub __my_module_MOD_my_sub)
      #   ^^^^^^^^     ^^^^^   ^^^^^^^^^     ^^^^^^
    include(FortranCInterface)

tells FortranCInterface to try given GLOBAL and MODULE manglings. (The carets point at raw symbol names for clarity in this example but are not needed.)