Thread: perror

Code:

if( (fp = fopen(name_ptr, mode_ptr)) == NULL){
		perror(name_ptr);
		exit(1);
	}

For some reason the fopen failed, but perror displayed the message "no error". Does anyone know why, after all fopen returns NULL when there is an error so perror should report it.
It only did this the once and I was just wondering why.