我有一个Node结构体，我在C中的堆栈实现中使用了该结构体：这是：

/* Do not modify */
#ifndef CQUEUE_H
#define CQUEUE_H

struct node_struct {
    char *data;
    struct node_struct *next;
};

typedef struct node_struct Node;

struct stack_struct {
    Node *head, *tail;
};

typedef struct stack_struct Stack;

我已经实现了通常在堆栈实现中找到的函数，如push，print等，但我似乎对我的pop函数有问题，下面是我的实现：

char* pop(Stack* q) {
    if (isEmpty(q)) {
        return NULL;
    }
    Node* temp = q->head;
    char* A = temp->data;
    q->head = temp->next;
    free(temp);
    return A;
}
int isEmpty(Stack* q) {
    return (q == NULL);
}

我有一个文件，我的预期输出应该是：

No items
//Push
a
b
c
//Pop
a
b
c

但我的代码

No items
//Push
a
b
c
//Pop
a
Segmentation fault

我的代码有什么问题？
编辑：如果有问题，这里是我的完整代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "stack.h" \\this is where the struct that I mentioned above is defined 

void push(Stack** q, char* word) {
    Node* newnode = (Node*)malloc(sizeof(Node));
    newnode->data = word;
    newnode->next = NULL;
    Stack* temp = *q;
    if (temp == NULL) {
        temp = (Stack*)malloc(sizeof(Stack));
        temp->head = newnode;
        temp->tail = newnode;
    } else {
        newnode->next = temp->head;
        temp->head = newnode;
    }
    *q = temp;
}

char* pop(Stack* q) {
    if (q == NULL) {
        return NULL;
    }
    Node* temp = q->head;
    char* A = temp->data;
    q->head = temp->next;
    free(temp);
    return A;
}


void print(Stack *q) {
    if (!isEmpty(q)) {
        Node *curr_node = q->head;
        while (curr_node != NULL) {
            printf("%s\n", curr_node->data);
            curr_node = curr_node->next;
        }
    } else {
        printf("No items\n");
    }
}

int isEmpty(Stack* q) {
    return (q == NULL);
}

void delete(Stack** q) {
    Stack* temp = *q;
    Node* curr_node = temp->head;
    while (curr_node != NULL) {
        Node* next_node = curr_node->next;
        free(curr_node->data);
        free(curr_node);
        curr_node = next_node;
    }
    free(temp);

       *q = NULL;
    }
    
int main(void) {
    Stack *q = NULL;

    // print the stack
    print(q);

    // push items
    push(&q, "a");
    push(&q, "b");
    push(&q, "c");
    print(q);

    // pop items
        while (!isEmpty(q)) {
            char *item = pop(q);
            printf("%s\n", item);
            free(item);
        }
    
        char *item = pop(q);
        assert(item == NULL);
    
        // push again
        push(&q, "d");
        push(&q, "e");
        push(&q, "f");
        print(q);
    
        // destroy the stack
        delete(&q);
    
        // print again
        print(q);
    
        // check copy
        char *s = (char *)malloc(10);
        strcpy(s, "Hello");
        push(&q, s);
        strcpy(s, "World");
        char *t = pop(q);
        printf("s = %s\n", s);
        printf("t = %s\n", t);
        free(t);
        free(s);
    
        // free the stack
        free(q);
    }