Funny bugs cause problem on understanding `fork()` syscall :)

print_buffer_every_time.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main(int argc, char const *argv[])
{
    printf("buffer:)) -> ");
    /* Fix: `fflush(stdout);` */

    for (size_t i = 0, p; i < 15; i++)
    {
        /* Fix: `if ((p = vfork()) == 0)` */
        if ((p = fork()) == 0)
        {
            printf("pid : %d\n", p);
            _exit(0);
        }
    }

    for (size_t i = 0; i < 15; i++)
        wait(NULL);

    return (EXIT_SUCCESS);
}

/**
 * output:
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> pid : 0
buffer:)) -> ⏎ 
 */

/**
 * Why repeating show unprinted buffer each time ?
 * Cause every process that created using fork syscall,
 * make a copy of .text, .data, stack, descriptors and ... of parent.
 * 
 * Every subprocess have a unflushed buffer copied from parent
 * that should flushed.
 * 
 * For fixing this problem you cah flush buffer before calling fork
 * or using vfork instead of fork syscall to share memory between processes
 * or using another ways that uses shared memory on multiple processes.
 * 
 */