Question

我正在使用推送和弹出功能创建一个简单的堆栈。我正在尝试将一系列字符串推入一个充当内存堆栈的数组中。但是，GDB一直告诉我，我没有正确地将字符串复制到数组中。任何人都有关于如何解决这个问题的想法？

/*************************************************************************
* stack.c
*
* Implements a simple stack structure for char* s.
************************************************************************/

// for strdup() in the testing code
#define _XOPEN_SOURCE 500

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

// the capacity of the stack
#define CAPACITY 10

//global variable used to keep track of pop and push

typedef struct
{
    // storage for the elements in the stack
    char* strings[CAPACITY];

    // the number of elements currently in the stack
    int size;
} stack;

// declare a stack (as a global variable)
stack s;

/**
 * Puts a new element into the stack onto the "top" of the data structure
 * so that it will be retrived prior to the elements already in the stack.
 */
bool push(char* str) 
{
    int i = 0;
    s.strings[i++] = strdup(str);
    ++s.size;
    return false;
}

/**
 * Retrieves ("pops") the last ("top") element off of the stack, following
 * the "last-in, first-out" (LIFO) ordering of the data structure. Reduces
 * the size of the stack.
 */
char* pop(void)
{
    int i = CAPACITY-1;
    return s.strings[i--];
}

/**
 * Implements some simple test code for our stack
 */
int main(void)
{
    // initialize the stack
    s.size = 0;

    printf("Pushing %d strings onto the stack...", CAPACITY);
    for (int i = 0; i < CAPACITY; i++)
    {
        char str[12];
        sprintf(str, "%d", i);
        push(strdup(str));
    }
    printf("done!\n");

    printf("Making sure that the stack size is indeed %d...", CAPACITY);
    assert(s.size == CAPACITY);
    printf("good!\n");

    printf("Making sure that push() now returns false...");
    assert(!push("too much!"));
    printf("good!\n");

    printf("Popping everything off of the stack...");
    char* str_array[CAPACITY];
    for (int i = 0; i < CAPACITY; i++)
    {
        str_array[i] = pop();
    }
    printf("done!\n");

    printf("Making sure that pop() returned values in LIFO order...");
    for (int i = 0; i < CAPACITY; i++)
    {
        char str[12];
        sprintf(str, "%d", CAPACITY - i - 1);
        assert(strcmp(str_array[i], str) == 0);
        free(str_array[i]);
    }
    printf("good!\n");

    printf("Making sure that the stack is now empty...");
    assert(s.size == 0);
    printf("good!\n");

    printf("Making sure that pop() now returns NULL...");
    assert(pop() == NULL);
    printf("good!\n");

    printf("\n********\nSuccess!\n********\n");

    return 0;
}

Answer 1

pop（）函数总是返回相同的字符串：

char* pop(void)
{
    int i = CAPACITY-1; // i is the same!
    return s.strings[i--]; // the same pointer
}

我建议将其更改为以下内容：

char* pop(void)
{
    if (s.size == 0) return NULL;
    char *str =  s.strings[--s.size];
    s.strings[s.size] = NULL;
    return str;
}

它可以避免您将过时的指针存储在堆栈中。

Answer 2

您的推送功能始终将字符串插入位置0。

改变如下：

bool push(char* str) 
{
    if (s.size == CAPACITY) return true;  // Stack is full!
    s.strings[s.size++] = strdup(str);
    return false;
}

有了pop（我从Michaels那里偷了这个回答并为空堆添加了警卫）：

char* pop(void)
{
    if (s.size == 0) return NULL;  // Stack is empty!
    char *str = s.strings[--s.size];
    s.strings[s.size] = NULL;
    return str;
}

如何将字符串复制到C中的数组？

2 个答案: