#include <stdio.h>
#include <string.h>
#include <string>
#include <sys/types.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>

class Base
{
        public:
                static pid_t ppid_c;
                static void   setppid(pid_t j){ ppid_c = j;}
                static pid_t getppid_c (){ return ppid_c;}
};
pid_t Base::ppid_c = 0;
void test (int signo)
{
        printf ("before sleep\n");
        sleep (3);
        printf ("after sleep 3 sec\n");
}
int main ()
{
        pid_t pid = fork ();
        if (pid > 0)
        {
                signal (SIGUSR1, test);
                printf ("ppid = %d", getpid ());
                fflush (stdout); /////////////////////////////////////////////////////////问题所在
                signal (SIGINT, SIG_IGN);
                int st;
                waitpid (pid, &st, 0);
        }else
                if (pid == 0)
                {
                        setsid ();
                        sleep (10);
                        Base::setppid (getppid ());
                        printf ("chiled sleep over\n");
                        printf ("child ppid = %d", Base::getppid_c ());
                        kill (Base::getppid_c (), SIGUSR1);
                        printf ("child program");
                        exit (0);
                }
}
在加上注释行以前..父进程居然不打印..郁闷了半天..最后组长想到这个问题printf ("ppid = %d", getpid ());
里边没有加\n 所以输出流先缓存起来.没有直接输出, 得手动清理