Question

I have a program written in Fortran by someone else which consequently reads a few things from the standard input and then does some calculations and outputs the result. What I want to do is to run it many times with different input data from another program, written in C by me. To do this I use popen:

  FILE *pipe = popen(".\\program.exe", "wt");
  if (!pipe) {
    exit(1);
  }

  fprintf(pipe, "%d\n", thing1);
  fprintf(pipe, "%d\n", thing2);
  ...

  pclose(pipe);

The problem is that it doesn’t work this way. It works perfectly with “program.exe < input.txt” but not this way. It reads the first thing and then outputs this stupid error: “IO-09 system file error – unknown error”. Of course I have no idea what this means as I’ve never programmed Fortran.

What am I doing wrong?

EDIT:

Unfortunately I have no source code of that program

Answer 1

It looks like it should work, not sure why it doesn’t. Are you sure
popen() is available on your Windows machine? I vaguely recall it
not being available for some Windows systems. You could try it with a
simple C program and see if it’s popen() or the Fortran program.

As a workaround, you could write your data to a temporary file, then
use system(".\\program.exe < tempfile") to call the Fortran program.
Yeah, it’s a kludge.