Fork returns the child pid (process identifier) in the parent process, using the waitpid parent can not if child is alive or not
Something like
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
pid_t cpid, w;
int status;
cpid = fork();
if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }
if (cpid == 0) { /* Code executed by child */
printf("Child PID is %ld\n", (long) getpid());
if (argc == 1)
pause(); /* Wait for signals */
_exit(atoi(argv[1]));
} else { /* Code executed by parent */
do {
w = waitpid(cpid, &status, WUNTRACED | WCONTINUED);
if (w == -1) { perror("waitpid"); exit(EXIT_FAILURE); }
if (WIFEXITED(status)) {
printf("exited, status=%d\n", WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
printf("killed by signal %d\n", WTERMSIG(status));
} else if (WIFSTOPPED(status)) {
printf("stopped by signal %d\n", WSTOPSIG(status));
} else if (WIFCONTINUED(status)) {
printf("continued\n");
}
} while (!WIFEXITED(status) && !WIFSIGNALED(status));
exit(EXIT_SUCCESS);
}
}
Output
$ ./a.out &
Child PID is 12345
[1] 12344
$ kill -STOP 12345
stopped by signal 19
$ kill -CONT 12345
continued
$ kill -TERM 12345
killed by signal 15
[1]+ Done ./a.out