CODEWITHSUNDEEP
c++fortran
J. Dowe
J. Dowe

Reputation: 99

trying to call fortran subroutine in c++

I have very limited knowledge of C++ and even less of fortran, I am currently trying to call a fortran subroutine from a c++ main. Following some examples I was able to come up with the following code to call the

subroutine fireballess(ear,ne,parames,ifl,photar,photer)

here is my C++ code:

#include <stdlib.h>
#include <stdio.h>
#include <iostream>

using namespace std;

extern "C" void fireballess_( double *fear, int fne,double* fparames, int fifl, double *fphotar, double *fphoter);

int main(int argc, char ** argv)
{
    int ne,ifl;
    double *ear;
    double *parames;

    double *photar;
    double *photer;


    parames = new double[9];

// parames=[4.3,0.23,0.5,0.5,1.5,1.,1000.,2.15,3.]
        parames[0]=4.3;
        parames[1]=0.23;
        parames[2]=0.5;
        parames[3]=0.5;
        parames[4]=1.5;
        parames[5]=1.;
        parames[6]=1000.;
        parames[7]=2.15;
        parames[8]=3.;

ne = 2;

    ear = new double[ne];
 ear[0] = 0.;
 ear[1] = 20.;
 ear[2] = 40.;
 ifl=2;

    photar = new double[ne];
    photer = new double[ne];

    // Call a Fortran subroutine
    //subroutine_sum_(&size,vec,&sum);
    fireballess_(&ear,ne,&parames,ifl,&photar,&photer);

    cout << "Calling a Fortran subroutine" << endl;
    cout << "===============================" << endl;

for (int i=0;i<=ne;i++){
    cout << "ear = " <<ear[i-1]<< " - "<<ear[i] << endl;
    cout << "photar = " << photar[i] << endl;
    cout << "photer = " << photer[i] << endl << endl;
}

    delete[] ear;
    delete[] parames;
    delete[] photar;
    delete[] photer;
}

however, when I try to compile I get the following error:

call_fortran.cpp: In function ‘int main(int, char**)’:
call_fortran.cpp:45:53: error: cannot convert ‘double**’ to ‘double*’ for argument ‘1’ to ‘void fireballess_(double*, int, double*, int, double*, double)’
     fireballess_(&ear,ne,&parames,ifl,&photar,photer);

which I do not understand, since the photer variable follows the very same path of the photar variable, that gives no errors instead. I hope someone with a better understanding of pointers than me can help me here. Thanks

Upvotes: 4

Views: 3943

Answers (1)

nada
nada

Reputation: 2117

ear is of type double* so that &ear is of type double**, which is not ok for the fortran function prototype. Getting rid of the &s might solve the issue (&parames, &photar and &photer are also double**):

Change

fireballess_(&ear,ne,&parames,ifl,&photar,&photer);

to

fireballess_(ear,ne,parames,ifl,photar,photer);

The fortran function prototype seems to be void fireballess_(double*, int, double*, int, double*, double). If that is really so, then photer still has to be changed to photer[i] where (i is an array-index like 0, 1, 2...).

If you really want to understand what is going on, I suggest reading a good C++ Pointer Tutorial.

Upvotes: 1

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