Programming

main()
{
  printf("demo of fork\n");
  fork();
  printf("hello");
}

demo of fork
hello hello

main()
{
  printf("demo of fork");
  fork();
  printf("hello");
}

demo of fork
hello hello demo of fork

// Without \n, this goes into a buffer and isn't printed yet.
printf("demo of fork");
// This creates a precise duplicate of the process -- including buffers.
// "demo of fork" will now be printed twice!
fork();
// this adds more stuff to the buffers of both programs.
printf("hello");
// The buffers will be flushed when the programs exit.  They may not exit
// in any particular order, and may try and print at the same time,
// causing the garble you see.

printf("demo of fork");
// Force it to print the buffer NOW, without waiting, so the child process
// doesn't get a copy of it in its own buffer.
fflush(stdout);
fork();
printf("hello");