c - Segmentation Fault (Core dumped)，但找不到故障

Question

#include <stdlib.h>
#include <stdio.h>
#include "stack.h"

struct stack {
    // ... SOME CODE MISSING HERE ...
    int top;
    int stackArray[STACK_SIZE];
    int push;
    int pop;
};

struct stack *stack_init() {
    struct stack* s = (struct stack*) malloc(sizeof(struct stack));
    s->top = 0;

    if (s == NULL)
        return NULL;
    else
        return s;
}

void stack_cleanup(struct stack* s) {

    for(int i = 0; i < STACK_SIZE; i++)
        s->stackArray[i] = 0;

    free(s);
}

int stack_push(struct stack *s, int c) {

    if (s->top <= STACK_SIZE){
        s->stackArray[s->top] = c;
        s->top++;
        s->push++;
        return 0;
    }
    else
        return 1;


}

int stack_pop(struct stack *s) {

    if (!stack_empty(s)){
        return s->stackArray[s->top];
        s->top--;
        s->pop++;
    }
    else
        return -1;
}

int stack_peek(struct stack *s) {

    if (!stack_empty(s)){
        return s->stackArray[s->top];
    }
    else
        return -1;
}

int stack_empty(struct stack *s) {

    if (s->top == -1)
        return 1;
    else
        return 0;
}

int main(){
    struct stack *test;
    // stack_peek(test);
    // return 0;
    printf("%d\n", test->top);
}

我正在尝试使用 C 为大学作业实现一个非常基本的堆栈，并且我正在尝试测试该实现，但它只给出了一个错误Segmantation fault (Core Dumped)。我在互联网上做了一些研究，但找不到可以帮助我的东西。我理解这Segmentation Fault Core Dumped意味着我正在访问一些我不能/不应该访问的东西，但我不知道这如何适用于我的代码。

谢谢。

标签： csegmentation-faultstack

Answer 1

最好的办法是使用 gdb 运行它，并在它出现段错误后使用 bt cmd 获取堆栈跟踪。我在您的初始代码中添加了一些注释，这些注释可能会或可能不会解决您的问题，但 main 显然被破坏了。main 中的“test”从未分配给任何东西，因此 test->top 试图取消引用分配给“test”的任何地址，这可能是当时“c 程序堆栈的内存”中的任何垃圾值。确保在使用变量之前对其进行初始化。

#include <stdlib.h>
#include <stdio.h>
#include "stack.h"

struct stack {
    // ... SOME CODE MISSING HERE ...
    int top;
    int stackArray[STACK_SIZE];
    int push;
    int pop;
};

struct stack *stack_init() {
    struct stack* s = (struct stack*) malloc(sizeof(struct stack));
    s->top = 0; // HERE IS A POTENTIAL NULL POINTER DEREFENCE, MOVE THIS AFTER THE NULL CHECK

    if (s == NULL)
        return NULL;
    else
        //HERE IS WHERE THE ABOVE LINE SHOULD BE LOCATED. s->top = 0;
        //WHAT ABOUT THE REST OF THE MEMORY IN THIS STRUCTURE, SHOULD IT BE 0?
        return s;
}

void stack_cleanup(struct stack* s) {

    for(int i = 0; i < STACK_SIZE; i++)
        s->stackArray[i] = 0;

    free(s);
}

int stack_push(struct stack *s, int c) {

    if (s->top <= STACK_SIZE){ //CAN s->top EVER BE NEGATIVE?
        s->stackArray[s->top] = c; //BECAUSE THIS WOULD BE A BAD INDEX IF IT WERE NEGATIVE HERE
        s->top++;
        s->push++;
        return 0;
    }
    else
        return 1;


}

int stack_pop(struct stack *s) {

    if (!stack_empty(s)){
        return s->stackArray[s->top];
        s->top--;//THIS LOOKS LIKE IT WILL NEVER GET EXECUTED
        s->pop++;//SAME WITH THIS LINE, MOVE THEM ABOVE THE RETURN STATEMENT IF YOU WANT THEM TO BE EXECUTED.
    }
    else
        return -1;
}

int stack_peek(struct stack *s) {

    if (!stack_empty(s)){
        return s->stackArray[s->top];
    }
    else
        return -1;
}

int stack_empty(struct stack *s) {

    if (s->top == -1)
        return 1;
    else
        return 0;
}

int main(){
    struct stack *test; //EITHER MALLOC MEMORY FOR THIS GUY OR PUT IT ON THE STACK (stack vs heap memory)
    //SAMPLE STACK USAGE, DOESNT USE YOUR INIT FUNCTION
    struct stack test;
    memset(test, 0, sizeof test);

    //IF YOU DONT WANT TO MALLOC YOU CAN POINT IT TO THE STACK VERSION ABOVE
    struct stack *test2 = &test; //NOW YOU DONT NEED MALLOC, BUT YOU STILL DIDNT USE YOUR SPECIAL INIT.
    // stack_peek(test);
    // return 0;
    printf("%d\n", test->top);
}

我所有引用堆栈的代码审查评论都指的是 ac 程序中的堆栈内存，而不是您在此处定义的结构（这也是一个堆栈，因此有点令人困惑）。 https://www.geeksforgeeks.org/memory-layout-of-c-program/