Question

So I’ve been working on this today and I’m pretty sure I’m close, but I’m still a bit confused on how to terminate child processes and if I’m doing this assignment correctly. Here’s the problem description:

Write a UNIX program that creates a child process that 
prints a greeting, sleeps for 20 seconds, then exits.
The parent process should print a greeting before creating 
the child, and another after the child has terminated. It 
should then terminate.

And here’s the code that I have:

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


int main()
{
    int child;

    printf("Parent Greeting\n");
    child = fork();
    if(child >= 0)
    {
        if(child == 0)
        {
            printf("Child process\n");
            sleep(2);
            printf("Child exiting\n");
            exit(0);
        }
    }
    else
    {
        printf("Failed\n");
    }
    printf("End");
    exit(1);
    return 0;
}

The issue I’m running into is how to properly terminate the child process. If I have the exit statements commented out, then the child will run, wait, and then the “End” statement will print. If I have the exit statements in, then the child process will say that it’s exiting and the program will just sit until I ctrl+c out of it. Any help would be appreciated, as I’m interested in the topic but am a bit confused 🙂 Thank you!

Answer 1

You don’t have to terminate the child process from the parent; it should terminate itself (and does after the sleep(), printf() and exit()). The parent process should wait() or waitpid() for the child to die before it prints the "End" message. Also, your "End\n" message should include a newline.

The exit(1); (at the end of the first program) is not wanted; it indicates failure. The exit() function does not return, so as written the return is redundant. But it would be better to remove the exit() and leave the return 0; indicating success.

(Note that the child should include a call to exit(), probably with the value 0 rather than 1 as in the revised code. After all, it has done its job successfully.)