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Detect pipe from running C program

I'm looking for a way to detect whether or not a program has been called from pipe, e.g.

Code:

whatever | my_program

versus simply just being exectuated directly:

Code:

my_program

Why? In the first case, I want to run the program non-interactively, and in the latter case I want to print out user-friendly messages. I've been thinking along the lines of some check I haven't yet found, like:

Code:

if( stream_buffer_is_not_empty() )

    print_interactive_messages();

Any ideas?

Thanks to you!

Jameson

Code:

#include <stdio.h>

#include <unistd.h>



int main (argc, argv)

  int argc;

  char** argv;

{

    if (isatty (STDIN_FILENO))

        printf ("Not a pipe.\n");

    else printf ("Its a pipe.\n");



    return 0;

}

The isatty function, as defined in unistd.h seems to work.