数据结构：用单链表实现的队列

#ifndef LINK_QUEUE_HEAD
#define LINK_QUEUE_HEAD
#include <stdio.h>
#include <stdlib.h>
#define Status int
#define OVERFLOW -1
#define OK 0
#define ERROR 1
typedef int ElemType;

typedef struct _Queue_Node {
    ElemType data;
    struct _Queue_Node *next;
} Node;

typedef struct {
    Node *front;//头指针
    Node *rear;//尾指针
} LinkQueue;

//初始化
Status init(LinkQueue *q)
{
    q->front = NULL;
    q->rear  = NULL;
    return OK;
}

//销毁队列，注意把队列中的元素全部销毁
Status destroy(LinkQueue *q)
{
    q->rear = q->front;
    while (q->rear != NULL){
        q->rear = q->rear->next;
        free(q->front);
        q->front = q->rear;
    }
    q->front = NULL;
    q->rear  = NULL;
    return OK;
}

//压入队列
Status push(LinkQueue *q, ElemType e)
{
    Node *p = (Node *)malloc(sizeof(Node));
    if (p == NULL) return OVERFLOW;

    p->data = e;
    p->next = NULL;

    if (q->front == NULL)//如果队列为空，则重置头指针
        q->front = p;
    else
        q->rear->next = p;//队列存在，则把当前尾部元素的next指向新入队元素
    q->rear = p;//重置尾指针
    return OK;
}

//出队
Status pop(LinkQueue *q, ElemType *e)
{
    Node *p;
    if (q->front == NULL) return OVERFLOW;
    *e = q->front->data;

    p = q->front;
    q->front = q->front->next;//front指针后移
    free(p);//已出队的元素需要销毁
    p = NULL;
    return OK;
}

#endif