在 C 中使用链表实现堆栈

Question

我用 C 语言编写了一个代码来使用 LinkedList 算法实现堆栈。这是代码............

#include<stdio.h>
#include<stdlib.h>
#include<limits.h>
struct listNode {
int data;
struct listNode *next;
};
struct stack{
struct stack *top;
};
struct stack *createstk(){
    struct stack *stk;
    stk=malloc(sizeof(struct stack));
    stk->top=NULL;
    return stk;
}
void push(struct stack *stk,int data){
    struct listNode *temp;
    temp=malloc(sizeof(struct listNode));
    if(!temp){
        printf("heap overflow");
        return;
    }
    temp->data=data;
    temp->next=stk->top;
    stk->top=temp;
}
int pop(struct stack *stk){
    if(isEmpty(stk))
        return INT_MIN;
    int data;
    struct listNode *temp;
    temp= stk->top;
    stk->top=stk->top->next;
    data=temp->data;
    delete(temp);
    return data;
}
int peek(struct stack *stk){
    if(isEmpty(stk))
        return INT_MIN;
    return stk->top->data;
}
int isEmpty(struct stack *stk){
    return stk->top==NULL;
}
void deleteStack(struct stack *stk){
    struct listNode *temp,*p;
    p=stk->top;
    while(p){
        temp=p->next;
        p=p->next;
        free(temp);
    }
    free(stk);
}
int main(){
    int i=0;
    struct stack *stk=createstk();
    for(i=0;i<=10;i++)
        push(stk,i);
    printf("Top Element is %d",peek(stk));
    for(i=0;i<=10;i++){
        printf("popped element is %d",pop(stk));
    }
    if(isEmpty(stk))
        printf("stack is empty");
    else
        printf("stack is not empty");
    deleteStack(stk);
    return 0;
}

[警告]来自不兼容指针类型的赋值。 正如您在图片中看到的那样。我是编码世界的新手，第一次遇到这个错误。这就是为什么我不知道该怎么办。请告诉我...

Answer 1

类型 stack 中的字段 top 类型错误。改变

struct stack {
    struct stack *top;
};

到

struct stack {
    struct listNode *top;
};

Answer 2

您有大量错误以stack->top 的错误类型开头，正如August Karlstrom 正确指出的那样，您的成员top 的类型必须是struct listNode *top;，例如

struct stack {
    struct listNode *top;
};

在更正之后，您必须对函数重新排序或提供 isEmpty() 和 deleteStack() 的函数原型。在它们第一次使用之前将它们移到你的代码中将解决问题，例如

struct stack *createstk()
{
    struct stack *stk;
    stk = malloc (sizeof (struct stack));
    stk->top = NULL;
    return stk;
}

int isEmpty (struct stack *stk)
{
    return stk->top == NULL;
}

void deleteStack (struct stack *stk)
{
    struct listNode *temp, *p;
    p = stk->top;
    while (p) {
        temp = p->next;
        p = p->next;
        free (temp);
    }
    free (stk);
}
...

接下来，这是 C，而不是 C++，没有 delete 函数来释放内存，所以在 pop() 中，您必须调用 free (temp); 而不是 delete (temp);。

最后，提供间距以使您的代码可读。结合上述内容，您可以执行以下操作：

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

struct listNode {
    int data;
    struct listNode *next;
};

struct stack {
    struct listNode *top;
};

struct stack *createstk()
{
    struct stack *stk;
    stk = malloc (sizeof (struct stack));
    stk->top = NULL;
    return stk;
}

int isEmpty (struct stack *stk)
{
    return stk->top == NULL;
}

void deleteStack (struct stack *stk)
{
    struct listNode *temp, *p;
    p = stk->top;
    while (p) {
        temp = p->next;
        p = p->next;
        free (temp);
    }
    free (stk);
}

void push (struct stack *stk, int data){

    struct listNode *temp;

    temp = malloc (sizeof *temp);
    if (!temp) {
        perror ("push()-malloc-temp");
        return;
    }

    temp->data = data;
    temp->next = stk->top;
    stk->top = temp;
}

int pop(struct stack *stk){

    int data;
    struct listNode *temp;

    if (isEmpty(stk))
        return INT_MIN;

    temp = stk->top;
    data = temp->data;
    stk->top = stk->top->next;

    free (temp);

    return data;
}
int peek(struct stack *stk){
    if(isEmpty(stk))
        return INT_MIN;
    return stk->top->data;
}

int main (void) {
    int i=0;
    struct stack *stk=createstk();

    for (i = 0; i <= 10; i++)
        push(stk,i);

    printf("Top Element is %d\n",peek(stk));

    for (i = 0; i <= 10; i++)
        printf ("  popped element is %d\n",pop(stk));

    if (isEmpty(stk))
        printf ("stack is empty\n");
    else
        printf ("stack is not empty\n");

    deleteStack(stk);

    return 0;
}

使用/输出示例

$ ./bin/stack_ll
Top Element is 10
  popped element is 10
  popped element is 9
  popped element is 8
  popped element is 7
  popped element is 6
  popped element is 5
  popped element is 4
  popped element is 3
  popped element is 2
  popped element is 1
  popped element is 0
stack is empty

内存使用/错误检查

在您编写的任何动态分配内存的代码中，对于分配的任何内存块，您都有 2 个职责：(1)始终保留指向起始地址的指针内存块，因此，(2) 当不再需要它时可以释放。

您必须使用内存错误检查程序来确保您不会尝试访问内存或写入超出/超出分配块的边界，尝试读取或基于未初始化的值进行条件跳转，最后，以确认您释放了已分配的所有内存。

对于 Linux，valgrind 是正常的选择。每个平台都有类似的内存检查器。它们都易于使用，只需通过它运行您的程序即可。

$ valgrind ./bin/stack_ll
==25935== Memcheck, a memory error detector
==25935== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==25935== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==25935== Command: ./bin/stack_ll
==25935==
Top Element is 10
  popped element is 10
  popped element is 9
  popped element is 8
  popped element is 7
  popped element is 6
  popped element is 5
  popped element is 4
  popped element is 3
  popped element is 2
  popped element is 1
  popped element is 0
stack is empty
==25935==
==25935== HEAP SUMMARY:
==25935==     in use at exit: 0 bytes in 0 blocks
==25935==   total heap usage: 12 allocs, 12 frees, 184 bytes allocated
==25935==
==25935== All heap blocks were freed -- no leaks are possible
==25935==
==25935== For counts of detected and suppressed errors, rerun with: -v
==25935== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

始终确认您已释放已分配的所有内存并且没有内存错误。

如果您还有其他问题，请告诉我。