C- 收割子进程和背景

Question

    pid_t pid;

    if ((pid == fork()) == 0){
            if (execvp(arg[0], arg) < 0) {
                printf("%s: Command not found.\n", arg[0]);
                exit(0);
            }

    }

    if (background == 0 )
    {
        int status;
        if (waitpid(pid, &status, 0) < 0)
            printf("waitfg: waitpid error");
        while(waitpid(-1, 0, WNOHANG) >= 0){}


    }
    else
    {
    printf("%d %s", pid, cmdline);
    }

I have this code for my program and I am trying to have the parent reap all child processes and the problem is that it is still not reaping. I am trying to use the code:

 while(waitpid(-1, 0, WNOHANG) >= 0){}

in order to reap but it seems to not get rid of the zombie process. What am I supposed to do to reap instead then

Also I am not sure if I am doing background right here.

Answer 1

Your code is wrong:

pid_t pid;

if ((pid == fork()) == 0){  // PROBLEM HERE
        if (execvp(arg[0], arg) < 0) {
            printf("%s: Command not found.\n", arg[0]);
            exit(0);
        }

}

you compare pid which isn't initialized with result of fork() => Undefined behavior (and after, you compare the result of this comparison with 0)

You should replace if ((pid == fork()) == 0){ by if ((pid = fork()) == 0){