cross_compile.md

• Ref:https://stackoverflow.com/questions/47957255/cmake-linking-fortran-against-static-c-library-fails
• ex.c

int get_key()
{
    return 10000;
}

• ex1.c

int get_key1()
{
    return 10001;
}

• ex.f08

program main
    implicit none

    interface
        function get_key() bind(c, name='get_key')
            use iso_c_binding
            integer(kind=c_int) :: get_key
        end function get_key
    end interface

    write(*, '(i0)') get_key()
end program main

• For c + fortran

gcc -c ex.c
gcc -c ex1.c
ar cr libex.a ex.o ex1.o
gfortran fex.f08 -L. -lex

• For C++ + fortran

g++ -c ex.c
g++ -c ex1.c
ar cr libex.a ex.o ex1.o
gfortran fex.f08 -L. -lex

• This yields undefined reference to 'get_key'
• Add extern "C" to ex.c and ex1.c. Then repeat the process

extern "C" int get_key()
{
    return 10000;
}

• If extern "C" is not used, then use -static with g++ command

g++ -static -c ex.c
g++ -static -c ex1.c
ar cr libex.a ex.o ex1.o
gfortran fex.f08 -L. -lex

In cmake, adjusting archive options

SET(CMAKE_C_ARCHIVE_CREATE "<CMAKE_AR> <LINK_FLAGS> cr ") SET(CMAKE_C_ARCHIVE_APPEND "<CMAKE_AR> <LINK_FLAGS> r ") SET(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> <LINK_FLAGS> cr ") SET(CMAKE_CXX_ARCHIVE_APPEND "<CMAKE_AR> <LINK_FLAGS> r ")