An animated processing icon, pure C

Question

I want to make an animated processing icon outputted in console via C.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

void render_processing_icon(int turnovers_qt) {
  char *icon_characters = "|/-\\\0";

  for (int i = 0; i < turnovers_qt * 8; i++) {
    printf("\b%c", icon_characters[i % 4]);

    usleep(500000); // sleep for a half of a second
  }

  printf("\n");
}

int main(int argc, char *argv[]) {
    render_processing_icon(2);

    printf("CONTROL MESSAGE\n");

    return 0;
}

But after usleep() time (0.5s * turnovers * 8) is over, program outputs this (without any animation, as you've guess):

$ \
$ CONTROL MESSAGE

sleep() works the same, BASH sleep via sytstem() too. I just have no idea what's the problem.

Answer 1

It is because you are not flushing the printf to the terminal. To save time the terminal usually buffers output. At some point when the buffer is full or in some terminals when you write \n to the stream it will flush automatically.

Try using fflush(stdout) before the usleep in your for loop to force this flush.