how to call a Fortran90 function included in a module in c++ code?

Question

I m including a fortran90 program that is not mine in my C++ project . In the first stept I try to call the function by their name_() and i get the error "undefined reference to mp_mpi_cartesian_init_ "by dispalying the symbol of the obj file (using nm) i found that the function are called by their module as module_function_ so i add the module name and i Get the same problem but between fortran obj such as "Constants.f90:(.text+0x36): undefined reference to __powi4i4" here is the c++ code : ``` #include #include using namespace std; extern"C" { void mod_save_wave_mp_read_it_psi_(int * it,complex* psi_E1E2 ); void mod_mpi_cartesian_mp_mpi_cartesian_init_( ); extern int mod_mpl_h_mp_iproc_ ; } int main(){ complex psi_local[512*24*512*24]; int it ; mod_mpi_cartesian_mp_mpi_cartesian_init_(); cout << "proc :" << mod_mpl_h_mp_iproc_ << "avant lecture "; mod_save_wave_mp_read_it_psi_(&it,psi_local); cout << "psi ="<< psi_local[0] << "poiur le proc "<

Accepted Answer

I am assuming you are using the g++, gfortran, mpif90 toolchain. If you have a module

```
module rocker
contains
subroutine bye_baby
...
end subroutine
```

The external C declaration for it in C++ is

```
extern "C"
{
    //          ,-- 2 Leading underscores to start
    //          | ,-- then the module name
    //          | |     ,-- then _MOD_
    //          | |     |    ,-- then the subroutine name
    //          V V     V    V
    extern void __rocker_MOD_bye_baby();
}
```

You may also need to add attribute((stdcall)) after the extern. By default, C assumes cdecl which stacks the parameters differently.

If you do not want the __rocker_MOD part, then the subroutine/function should not be declared in a module.

how to call a Fortran90 function included in a module in c++ code?

Solution

Problem