Fortran (compiling and using Fortran code within C/C++)

• to compile fortran code and use within a C/C++ program
  // prog.f: 
  subroutine square(n,out)  
     integer n 
     integer out 
     out=n*n 
     return  
  end subroutine square 
  //master.C: 
  extern C void square_(int *n, int *out); 
  void main(){ 
     int *input; 
     *input =3; 
     int *output; 
     square_(input,output); 
     cout *output « endl;  // returns 9 
  }

1. compile the fortran routines:  >g77 prog.f -c -ffree-form
   the -ffree-form argument allows you to get away from the very picky fixed-form Fortran requirements (sometimes this doesn't work and you need to remove this option)
2. in the C++ code, declare the fortran function with _ at the end of the name and pass all arguments by reference, noting that prog.f declares them as non-pointers (if the fortran function is named in all caps, make sure the C/C++ references to it are lower case, otherwise you may fail to link properly
   extern C void functionname_(args...) // declaring the function 
   functionname_(args...)// using the function
3. compile the C++ code: >g++ -c master.C
4. link:  >g++ master.o prog.o
5. you may need to use -lf, -lfortran or -lg2c in the linking