链表实现中的堆栈错误 [英] Error in stack with linked list implementation

问题描述

我正在尝试使用链表实现来实现堆栈.它给了我分段错误".请帮助我找到错误.这是我的代码:

I'm trying to implement stack using linked list implementation. Its giving me "Segmentation Error". Please help me finding the error. This is my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 100

struct NODE {
    char word;
    struct NODE *next;
};

struct STACK {
    struct NODE *head;
    int size;
};

void pushStack(struct STACK *stack, char s);
void makeStack(struct STACK *stack, char *s);
void printStack(struct STACK *stack);

int main(){
    char *s;
    fgets(s,100,stdin);
    struct STACK stack;
    stack.head = NULL;
    makeStack(&stack,s);
    printStack(&stack);
    return 0;
}

void pushStack(struct STACK *stack, char s){
    struct NODE temp;
    temp.word = s;
    temp.next = stack->head;
    stack->head = &temp;
}

void makeStack(struct STACK *stack, char *s){
    char temp[MAX];
    strcpy(temp,s);
    for(int i=0; i<MAX; i++){
        if(temp[i]=='\0') break;
        pushStack(stack,temp[i]);
    }
}

void printStack(struct STACK *stack){
    struct NODE *trav = stack->head;
    while (trav != NULL){
        printf("%c", trav->word);
        trav = trav->next; 
    }
}

MAX = 100是我对字符串输入的限制.我还没有添加增加大小的功能，因为我现在暂时忽略了大小的增加.在我完善实施之前

MAX=100 is the limit I'm taking for string input. I haven't also added increasing the size because I'm just ignoring the increment of size for now. Before I could perfect the implementation

推荐答案

在 main 中， s 指针未初始化，并且指向无处.

In main the s pointer is not initialized and it points nowhere.

int main(){
   char *s;   // <<< this is wrong, you want 'char s[100]' instead
   fgets(s,100,stdin);
   ...

但这是最安全的选择:

 int main(){
   char s[100];                 // declare array of 100 chars
   fgets(s, sizeof(s), stdin);  // sizeof(s) is the actual size of s (100 here)
   ...

这也是错误的:您将指针存储到本地变量 temp ，但是一旦从 pushStask 函数返回，该变量便不复存在.

This is wrong too: you store the pointer to the local variable temp, but that variables ceases to exist once you return from the pushStask function.

void pushStack(struct STACK* stack, char s) {
  struct NODE temp;
  temp.word = s;
  temp.next = stack->head;
  stack->head = &temp;
}

相反，您需要像这样创建一个新的 struct NODE :

Instead you need to create a new struct NODE like this:

void pushStack(struct STACK* stack, char s) {
  struct NODE* temp = malloc(sizeof *temp);
  temp->word = s;
  temp->next = stack->head;
  stack->head = temp;
}

您可以编写 sizeof(struct NODE)而不是 malloc(sizeof * temp)，它是相同的，但是它不够安全，因为您可能会错误地编写 sizeof(struct STACK)可以正常编译，但是分配的内存大小错误.

Instead of malloc(sizeof *temp) you could write sizeof(struct NODE), it's the same, but it's less fool proof because you could mistakenly write sizeof(struct STACK) which would compile fine, but the size of the allocated memory would be wrong.

另一个问题:您没有分配 struct STACK 的 size 字段，现在这不是问题，但是以后可能会成为问题.

Another problem: you don't assign the size field of the struct STACK, this is not a problem now, but it might become a problem later.

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