The following program doesn't "seem" to print "hello-out". (Try executing it)
  #include <stdio.h>
  #include <unistd.h>
  int main()
  {
          while(1)
          {
                  fprintf(stdout,"hello-out");
                  fprintf(stderr,"hello-err");
                  sleep(1);
          }
          return 0;
  }
话说hello-out真的没有出现，去哪里了？不理解！

谢谢你的链接，看过了，stdout原来是缓冲的！
下次注意自己的说话方式了