main()函数中的结构体变量q调用initqueue()初始化失败了，不知道为什么，我明明用了地址来调用初始化函数的

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef int elemtype;
struct Node {
    struct Node* next;
    elemtype data;
};
typedef struct Node node;
node* getnode(elemtype x, node* nextptr) {
    node* n;
    n = (node*)malloc(sizeof(node));
    n->data = x;
    n->next = nextptr;
    return n;
}

typedef struct {
    node* front;
    node* rear;
    int length;

}swlqueue;

void  initqueue(swlqueue* qd) {
    qd = (swlqueue*)malloc(sizeof(swlqueue));
    qd->front = getnode(0, NULL);
    qd->rear = qd->front;
    qd->length = 0;
}

void insertafter(node* n, node* p) {
    p->next = n->next;
    n->next = p;
}



void in(swlqueue* q, elemtype x) {
    node* newnode;
    newnode = getnode(x, NULL);
    if (q->length == 0)
        insertafter(q->front, newnode);
    insertafter(q->rear, newnode);
    q->rear = newnode;
    q->length++;
}

elemtype out(swlqueue* q) {
    node* n;
    elemtype x;
    x = ((q->front)->next)->data;
    n = q->front;
    q->front = (q->front)->next;
    free(n);
    q->length--;
    return x;
}

int main() {
    swlqueue q;
    initqueue(&q);
    int array[20];
    memset(array, 0, sizeof(array));
    for (int i = 0; i <= 50; i++)
        in(&q, i);
    for (int j = 0; j < 20; j++)
        array[19 - j] = out(&q);
    for (int k = 0; k <= 19; k++)
        printf("%d\n", array[k]);
    system("pause");
    return 0;


}

需要双指针

问题解决的话，请点采纳

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef int elemtype;
struct Node {
    struct Node* next;
    elemtype data;
};
typedef struct Node node;
node* getnode(elemtype x, node* nextptr) {
    node* n;
    n = (node*)malloc(sizeof(node));
    n->data = x;
    n->next = nextptr;
    return n;
}

typedef struct {
    node* front;
    node* rear;
    int length;

}swlqueue;

void  initqueue(swlqueue** qd) {
    *qd = (swlqueue*)malloc(sizeof(swlqueue));
    (*qd)->front = getnode(0, NULL);
    (*qd)->rear = (*qd)->front;
    (*qd)->length = 0;
}

void insertafter(node* n, node* p) {
    p->next = n->next;
    n->next = p;
}



void in(swlqueue* q, elemtype x) {
    node* newnode;
    newnode = getnode(x, NULL);
    if (q->length == 0)
        insertafter(q->front, newnode);
    insertafter(q->rear, newnode);
    q->rear = newnode;
    q->length++;
}

elemtype out(swlqueue* q) {
    node* n;
    elemtype x;
    x = ((q->front)->next)->data;
    n = q->front;
    q->front = (q->front)->next;
    free(n);
    q->length--;
    return x;
}

int main() {
    swlqueue *q;
    initqueue(&q);
    int array[20];
    memset(array, 0, sizeof(array));
    for (int i = 0; i <= 50; i++)
        in(q, i);
    for (int j = 0; j < 20; j++)
        array[19 - j] = out(q);
    for (int k = 0; k <= 19; k++)
        printf("%d\n", array[k]);
    system("pause");
    return 0;


}