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 ifx
Demonstrate linking of
- C and C++ program calling Fortran libraries
- Fortran program calling C and C++ libraries
We assume the compilers are C++11 and Fortran 2018 capable.
This repo's examples are also known to work with:
- NVidia HPC SDK (nvc++, nvfortran)
- AOCC AMD Optimizing Compliers
- Cray compilers (cc, ftn)
In general, avoid the FortranCInterface of CMake and mangling function names.
Instead, use Fortran 2003 standard bind(C)
.
Other real-world examples include fortran-filesystem using C++ stdlib filesystem from Fortran and standard sleep implementation as used in blocktran and Fortran Standard Library.
cmake -B build
cmake --build build
ctest --test-dir build
Note the use of CMake target property LINKER_LANGUAGE necessary for CMake with Intel oneAPI on Linux / macOS.
- C main program with Fortran library:
LINKER_LANGUAGE C
- C++ main program with Fortran library:
LINKER_LANGUAGE CXX
- Fortran main program with C or C++ library:
LINKER_LANGUAGE Fortran
add_executable(f_main main.f90 lib.cpp)
set_property(TARGET f_main PROPERTY LINKER_LANGUAGE Fortran)
add_executable(c_main main.c lib.f90)
set_property(TARGET c_main PROPERTY LINKER_LANGUAGE C)
add_executable(cpp_main main.cpp lib.f90)
set_property(TARGET cpp_main PROPERTY LINKER_LANGUAGE CXX)
While the examples prioritize C++, there are also several companion C examples to go with the C++ examples. There are also some Fortran main programs calling C or C++.
The examples "array", "malloc", "vector" show distinct ways to send arrays to/from Fortran with C and C++.
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.
On 2019-01-12 a GCC commit from Paul Thomas brought ISO_Fortran_binding.h to GCC 9.
This means if using Clang compiler e.g. on macOS, you may need to switch to GCC (till Clang/Flang someday includes ISO_Fortran_binding.h).
GCC ≥ 9 and Intel oneAPI have ISO_Fortran_binding.h
Some examples use scalar C struct. ISO_C_BINDING handles mapping struct to/from Fortran TYPE. For arrays of struct, compiler pragma may be needed.
Valgrind needed suppression to avoid memory alignment (uninitialized memory) warnings for C struct input to nanosleep.
For MacOS with Apple's Clang and Homebrew GCC, it MAY be needed to 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