C: fork() child processes

Question

According to the textbook I am reading, the code below creates N child processes that will exit with unique statuses.

/* Parent creates N children */
for (i = 0; i < N; i++)
    if ((pid[i] = Fork()) == 0) /* Child */
        exit(100+i);

Earlier in the textbook, it states that the following code will have 8 lines of output:

int main(){
    Fork();
    Fork();
    Fork();
    printf("hello\n");
    exit(0);
}

This leads me to believe that there are 2^n child processes, where n is the number of times fork() is called. Is the reason the first code only produces N child processes (as opposed to 2^N) because the child exits every time, so by the time the subsequent fork() is called, it only operates on the parent process?

in the second case all the children continue on forking and printing. In the first case the child exits as soon as it is created so only the parent continues — Jerry Jeremiah
You should probably mention which book you're using. I know Stevens "UNIX Network Programming" uses the initial-capital system call names to specify the error-checked versions of system calls. — Jonathan Leffler
@JonathanLeffler Sorry for the confusion, I am using CS: A Programmer's Perspective, and the capitalized version of fork() is intended to mean the error-checked version as well. — user2821275

Yu Hao Yu Hao · Accepted Answer · 2014-02-17T03:38:11

Every successful call to fork(), creates a new process.

In the first example, the children processes (the return value of fork() being 0) call exit();, which means they won't call the next fork().

In the second example, every children process continues forking.

C: fork() child processes

2 Answers