Creating multiple processes in C - c

Question

I am writing a program that needs to create multiple processes. Let's say this number is 3. I want each of these processes to count and output from 1 to 5, and to sleep for 1 second between each count/output. I tried to do that in a following manner, but my sleep(1) did not work like it was being interrupted. I would appreciate some background on the topic, what i did wrong, and how to resolve this. Here is my code so far.
/*
* Creates N > 2 processes.
*/
int main(int argc, const char * argv[])
{
pid_t pid;
for(int i = 0; i < N_PROC; i++) {
pid = fork();
if(pid == 0) {
ProcessWork();
exit(0);
}
}
}
/*
* Work of a single process.
*/
void ProcessWork() {
char buffer[BUF_SIZE];
for (int i = 1; i <= 5; i++) {
sleep(1);
sprintf(buffer, "PID = %d, count = %d\n", getpid(), i);
write(1, buffer, strlen(buffer));
}
}

Answer 1

Your sleep() works exactly as it should work. However, your problem seems to be that the parent process does not wait for the termination of the child processes, so the parent process terminates before the children have performed the work. Thus, it looks like this on a Unix system:
% ./a.out
% PID = 41431, count = 1
PID = 41430, count = 1
PID = 41432, count = 1
PID = 41431, count = 2
PID = 41430, count = 2
PID = 41432, count = 2
PID = 41430, count = 3
PID = 41431, count = 3
PID = 41432, count = 3
PID = 41430, count = 4
PID = 41431, count = 4
PID = 41432, count = 4
PID = 41431, count = 5
PID = 41430, count = 5
PID = 41432, count = 5
You should take a look at the manual page of the wait() system call. You can call that system call in a loop, and it returns the pid of the terminated child as long as there are children, and -1 with errno == ECHILD once you've run out of children. That ECHILD can be used as the loop termination criterion.

Answer 2

Wait for forked process termination, if I understood your problem...
int main(int argc, const char * argv[])
{
pid_t pid[N_PROC];
for(int i = 0; i < N_PROC; i++) {
pid_t cur_pid = fork();
if(cur_pid == 0) {
pid[i] = cur_pid;
ProcessWork();
exit(0);
}
}
for(int i = 0; i < N_PROC; i++)
wait(&pid[i]);
}