Can Parent Process terminate without executing the Child Process?

Question

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
    //fork();
    //printf("Hello World\n");
    int i=fork();
        // child process because return value zero
    if (i == 0)
        printf("Hello from Child! %d \n",i);
 
    // parent process because return value non-zero.
    if (i!=0)
        printf("Hello from Parent! %d \n",i);

    return 0;
}

Why the first output is giving two print output while other are only giving outputs from the Parent Only - when fork() creates two processes.

I am expecting two output print in each output case because of the existence of two process.

Can anyone explain why ?

Output 1:

Hello from Parent! 600 
Hello from Child! 0

Output 2:

Hello from Parent! 8206

Output 3:

Hello from Parent! 350

Output 4:

Hello from Parent! 1098

Why the first output is giving two print output while other are only giving single outputs from the Parent Only - when fork() creates two processes. I am expecting two output print in output case.

Can't reproduce.... I get both prints every time I run the program — Support Ukraine, Mar 13 '23 at 11:03
You might want to `wait` until the child exits (and the child should probably exit explicitly, not just return from `main`). — Hasturkun, Mar 13 '23 at 11:19
What operating system? What compiler? What compiler options? — Andrew Henle, Mar 13 '23 at 11:29

score 1 · Answer 1 · answered Mar 13 '23 at 11:13

1

Make sure the child process is successfully terminated. You can run additional code to ensure the child process is terminated before the parent process.

int pid = fork();
//...............
kill(pid, SIGKILL);

EDIT: See this answer: How to kill child of fork?

answered Mar 13 '23 at 11:13

Vahan

166
13

How would doing this change whatever string the child process prints? Outside of killing it before it printed anything? – Andrew Henle Mar 13 '23 at 11:26
I figured any call to fork() after the first child process is created will not create a new process, since an identical child process is already running. Killing the child process before exiting parent process would ensure that won't happen. – Vahan Mar 13 '23 at 11:29

score 0 · Answer 2 · answered Mar 13 '23 at 11:33

Given this code

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
    //fork();
    //printf("Hello World\n");
    int i=fork();
        // child process because return value zero
    if (i == 0)
        printf("Hello from Child! %d \n",i);
 
    // parent process because return value non-zero.
    if (i!=0)
        printf("Hello from Parent! %d \n",i);

    return 0;
}

if fork() were to fail, it would generate the output you're seeing.

This code will tell you why fork() fails:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
    //fork();
    //printf("Hello World\n");
    pid_t i=fork();
    if (i < 0)
        perror( "fork() failed" );
        // child process because return value zero
    if (i == 0)
        printf("Hello from Child! %d \n",( int ) i);
 
    // parent process because return value non-zero.
    if (i!=0)
        printf("Hello from Parent! %d \n", ( int ) i);

    return 0;
}

Also, note that fork() returns pid_t, not int. They don't have to be the same.

Can Parent Process terminate without executing the Child Process?

2 Answers2