数据结构链表输出是随机值？

Question

#include<stdio.h>
#include<malloc.h>
#define QElemtype int
#define status int

typedef struct QNode {
QElemtype data;
struct QNode* next;
}QNode,*QueuePtr;

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

status InitQueue(LinkQueue* Q) {
Q->front = Q->rear = (QNode*)malloc(sizeof(QNode));
Q->front->next = NULL;
return 1;
}

status EnQueue(LinkQueue* Q, int e) {
QNode* p = (QNode*)malloc(sizeof(QNode));
p->next = NULL;
p->data = e;
Q->rear->next = p;
}
status InQueue(LinkQueue* Q, int* e) {
QNode* p = (QNode*)malloc(sizeof(QNode));
p = Q->front->next;
e = p->data;
Q->front->next = p->next;
free(p);
}

status ReadLinkQueue(LinkQueue* Q) {
return Q->front->data;
}
int main()
{
LinkQueue Q;
InitQueue(&Q);
EnQueue(&Q, 1);
printf("%d", ReadLinkQueue(&Q));
}

为什么输出值是随机值而不是我想要的数字1呢？

Answer 1

修改如下，见注释，供参考：

#include<stdio.h>
#include<malloc.h>
#define QElemtype int
#define status int

typedef struct QNode {
    QElemtype data;
    struct QNode* next;
}QNode, * QueuePtr;

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

status InitQueue(LinkQueue* Q) {
    //Q->front = Q->rear = (QNode*)malloc(sizeof(QNode));修改
    Q->rear = Q->front = NULL;    //修改
    return 1;
}

status EnQueue(LinkQueue* Q, int e) {
    QNode* p = (QNode*)malloc(sizeof(QNode));
    p->next = NULL;
    p->data = e;
    if (Q->rear != NULL)   //修改
        Q->rear->next = p; //修改
    else
        Q->front = p;      //修改  队头
    Q->rear = p;           //修改  队尾
    return 1;      //修改
}
status InQueue(LinkQueue* Q, int* e) {
    //QNode* p = (QNode*)malloc(sizeof(QNode));修改
    if (Q->front == NULL) {    //修改
        Q->rear = NULL;        //修改
        *e = -1;               //修改
        return 0;              //修改
    }
    QNode* p = Q->front;      //修改
    Q->front = p->next;       //修改
    *e = p->data;  //e = p->data; 修改
    free(p);
    return 1;    //修改
}

status ReadLinkQueue(LinkQueue* Q) {
    if (Q->front == NULL) return 0;
    return Q->front->data;
}
int main()
{
    int e;
    LinkQueue Q;
    InitQueue(&Q);//初始化队列

    EnQueue(&Q, 1);//入队
    EnQueue(&Q, 2);
    EnQueue(&Q, 3);
    EnQueue(&Q, 4);

    printf("队头元素值：%d\n\n", ReadLinkQueue(&Q));
    
    printf("出队:\n");
    InQueue(&Q, &e);//出队
    printf("%d\n", e);

    InQueue(&Q, &e);
    printf("%d\n", e);

    InQueue(&Q, &e);
    printf("%d\n", e);

    InQueue(&Q, &e);
    printf("%d\n", e);

    InQueue(&Q, &e);
    printf("%d\n", e);

    return 0;
}