Fortran subroutines and functions are easily called from C and C++.

Use the standard C binding to define variable and bind functions/subroutines.

This project is also a way to quickly check if compilers you have are ABI-compatible. For example:

• Clang and Gfortran
• (Windows) MSVC and Intel oneAPI ifort

Demonstrate linking of

• C and C++ program calling Fortran libraries
• Fortran program calling C and C++ libraries

In general, strongly avoid the FortranCInterface of CMake and mangling function names--just use Fortran 2003 standard bind(C)

cmake -B build

cmake --build build

ctest --test-dir build

For MacOS with Apple's Clang and Homebrew GCC, be sure you have in ~/.zshrc like the following: (check directory / versions on your Mac)

export LIBRARY_PATH=$LIBRARY_PATH:/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib
export CPLUS_INCLUDE_PATH=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include
export CXXFLAGS=-I$CPLUS_INCLUDE_PATH
export CFLAGS=$CXXFLAGS

Using Fortran statement "stop" or "error stop" with a C/C++ main program works like with a Fortran main program. The "error*" examples show this.

• StackOverflow