在C语言中用typedef不都是：

typedef struct
{
.....
}XX;
XX xx;  吗？

为什么可以这样：
1.
typedef struct node *pointer;     //在定义 node 之前使用 node?
struct node
{
    int data;
    pointer next;
};
2.
typedef struct QNode            //为什么会出现 QNODE 两次？
{
   int data;
   struct QNode * next;
}QNode, * QueuePtr;

#include <stdio.h>
#include<stdlib.h>
#include<iostream.h>
typedef struct QNode{
   int data;
   struct QNode * next;
}QNode, * QueuePtr;


typedef struct
{
   QueuePtr front;
   QueuePtr rear;
}LinkQueue;
LinkQueue Q;

int InitQueue( )
{
    QueuePtr p;

     Q.front=Q.rear=(QueuePtr)malloc(sizeof(QNode));
     if(!Q.front)
     {
        printf("OVERFLOW");
        return 0;
     }
     p->next=NULL;
     return 1 ;
}

void DestroyQueue( )
{
     while(Q.front)
     {
       Q.rear=Q.front->next;
       free(Q.front);
       Q.front=Q.rear;
     }
}

int EnQueue ( )
{
    QueuePtr p;
    int e;

    p=(QueuePtr)malloc(sizeof(QNode));
    if(!p)
    {
        printf("OVERFLOW");
        return 0;
    }

    printf("Input the data:\n");
    scanf("%d",&e);

    p->data=e;
    p->next=NULL;
    Q.rear->next=p;
    Q.rear=p;
}
void DeQueue( )
{
  int e;
  QueuePtr p;

  if(Q.front==Q.rear)
    {
        printf("The queue is empty!\n\n");
        return ;
    }

  p=Q.front->next;
  e=p->data;

  printf("The top data is:  %d\n\n",e);

  Q.front->next=p->next;
  if(Q.rear==p) Q.rear=Q.front;

  free(p);
}

void PrintQueue( )
{
     QueuePtr p;
     int i=1;

     if(Q.front==Q.rear)
     {
        printf("ERROR!\nThe Queue is empty!\n");
        return ;
     }

     printf("The Queue is:\n");

     p=Q.front->next;

     while(p!=Q.rear)
     {
        printf("%d     %d\n",i++,p->data);
        p=p->next;
     }

     printf("%d     %d\n\n",i,p->data);
}

int main()
{
  int i=1;

  while (i)
  {
    printf("1.        Create a Queue\n");
    printf("2.        Destroy the Queue\n");
    printf("3.        Insert a data\n");
    printf("4.        Delete a data\n");
    printf("5.        Print the Queue\n");
    printf("0.        Exit\n\n");
    printf("What do you want to do?\n");

    scanf("%d",&i);
    switch(i)
    {
        case 1:   InitQueue();break;
        case 2:   DestroyQueue();break;
        case 3:   EnQueue();break;
        case 4:   DeQueue();break;
        case 5:   PrintQueue();break;
        case 0:   return 1;

        default:  printf("ERROR!  Try again!\n");
    }
   }

    

    return 1;
}

以上就是源程序
谢了


对了，我还试了一下，似乎QNode还是类型名