父子进程通信同步之管道

static int pfd1[2],pfd2[2];
void err_sys(char *str)
{
  printf("%s\n",str);
  exit(1);
}
void err_quit(char *str)
{
  printf("%s\n",str);
  exit(0);
}
void TELL_WAIT(void)
{
  if(pipe(pfd1)<0||pipe(pfd2)<0)
    err_sys("pipe error");
}
void TELL_PARENT(pid_t pid)
{
  if(write(pfd2[1],"c",1)!=1)
    err_sys("write error");
}
void WAIT_PARENT(void)
{
   char c;
   if(read(pfd1[0],&c,1)!=1)
     err_sys("read error");
  if(c!='p')
    err_quit("WAIT_PARENT:incorrect data");
   else
     printf("parent is %c\n",c);
}
void TELL_CHILD(pid_t pid)
{
  if(write(pfd1[1],"p",1)!=1)
    err_sys("write error");
}
void WAIT_CHILD(void)
{
  char c;
  if(read(pfd2[0],&c,1)!=1)
    err_sys("read error");
  if(c!='c')
    err_quit("WAIT_CHILD: incorrect data");
  else
    printf("child is %c\n",c);
}
int main(void)
{
  pid_t pid;

  TELL_WAIT();
  pid=fork();
  if(pid<0)
    err_sys("fork failed");
  else if(pid>0){
    close(pfd2[0]);
    TELL_PARENT(pid);
    close(pfd1[1]);
    WAIT_PARENT();
  }else{
    close(pfd1[0]);
    TELL_CHILD(pid);
    close(pfd2[1]);
    WAIT_CHILD();
  }
  return 0;
}