Why Would WIFEXITED Return True on Running Process?

Question

When I wait on a specific running process group that is a child process, WIFEXITED returns true saying the process exited? Is this the way it works? Seems there is something I am not understanding....

if ( waitpid(-pgid, &pstatus, WUNTRACED|WNOHANG ) == -1)
    perror("Wait error");

if ( WIFEXITED(pstatus) ) {
    strncpy(buf,  "Exited", buf_size);
    return 0;

Answer 1

As you specified WNOHANG I think waitpid is returning 0 and pstatus has the value it had before so WIFEXITED is not working with updated data.

if WNOHANG was specified and one or more child(ren) specified by pid exist, but have not yet changed state, then 0 is returned.