Pipe both stdin and stdout from a sub-process

[alkis]

I have a program A that is in a forever (kind of) I/O loop. Reads stdin, and prints results in stdout.

I want program B to start program A and send it input and read it's output.

Let me give some samples

Program A

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[]) {
  char buf[80];
  int val;

  while (fgets(buf, 80, stdin)) {
    if (buf[strlen(buf)-1] == '\n')
      buf[strlen(buf)-1] = '\0';
    if (!strcmp(buf, "quit"))
        break;
    val = atol(buf);
    printf("%d\n", val+val);
    fflush(stdout);
  }
  printf("Something happened\n");
  return 0;
}

So Program A, reads from stdin and if you happen to enter an integer it doubles it and outputs the result and stays in the loop. (Well, if you type "quit" it ends)

Researching for the problem seems like the way to go is to open two pipes on the sub-process. Use one for sending to stdin, and use the other to read from stdout (of the sub-process).

So, I started from libnix's popen and tried to extend it so it opens two pipes.

The thing that fails is reading from sub-process output. It seems to never send anything to that pipe.

In the archive you'll find three files.

simple.c is standalone (m68k-amigaos-gcc -o simple simple.c)
drive2.c test.c should compile together (m68k-amigaos-gcc -o test drive2.c test.c)
Finally test should send input to simple and read it's output.

How should I tackle this? Maybe some other way?

[idrougge]

I think the real Amiga way is to use a MessagePort.

[alkis]

Originally Posted by idrougge

I think the real Amiga way is to use a MessagePort.

True that. It's just that I might need to handle an "amiga unaware" application. For instance, a uci chess engine https://github.com/alexalkis/sillychess ;-)