wait()

An example of UNIX System Calls. Useful for a parent to wait for a child process to finish what its been doing.

• waitpid() is a more complete version

Here is an example using wait():

int main (int argc, char *argv[]){
 
	printf("hello world (pid:%d)\n", (int) getpid());
 
	int rc = fork();
 
	if (rc < 0){ // fork failed
		fprintf(stderr, "fork failed\n")
	}
 
	else if (rc == 0){ // child (new process)
		printf("hello, I am child (pid:%d)\n", (int) getpid());
	} 
 
	else {
		int wc = wait(NULL);
		printf("hello, I am parent of %d (wc:%d) (pid:%d)\n", 
				rc, wc, (int) getpid())
	}
	
	return 0;
}

prompt> ./p2
hello world (pid:29266)
hello, I am child(pid:29267)
hello, I am parent of 29267 (wc:29267) (pid:29266)
prompt>

In this code, if the parents run first such that rc > 0, it will immediately call wait(), which won’t return until the child has run and exited. Thus, even if the parent runs first it’ll wait for the child to finish