C语言 单链表实现推送和弹出段故障

Question

我正在查看一些旧代码来编写一个程序(用C语言)，该程序创建push和pop方法，类似于单个链表的堆栈。我目前得到一个分割错误，不能找出这个问题。

任何push的输入都是单个字符，下面是一个输入示例:
推动;
推动g
推动。
流行
Push -

代码(注释掉一些导致错误的东西):

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct node
{
    char data;
    struct node* next;
}*top = NULL;
void push(char c);
char pop();
int main(int argc, char *argv[])
{
    char* p1;
char p2;
FILE *fp = NULL;
fp = fopen(argv[2], "r");
loop:
    while (!feof(fp)) 
    {
        fscanf(fp,"%s", &p1);
        while (strcmp(&p1,"push") == 0) 
        {
            fscanf(fp,"%s", &p2);
            printf("%sn", &p2); 
            // push(&p2);
            fscanf(fp,"%s", &p1);
            if (strcmp(&p1,"pop") == 0) 
            {
                //pop();
                 fscanf(fp,"%s", &p1);
            }
        }
        while (strcmp(&p1,"pop") == 0) 
        {
            //pop();??
            fscanf(fp,"%s",&p1);
            if (strcmp(&p1,"push") == 0) 
            {
                fscanf(fp,"%s",&p2);
                printf("%sn",&p2); 
                // push(&p2);
            }
            goto loop;
         }
    }
    fclose(fp);
    return 0;   
}
void push(char c) 
{
    struct node *temp;
    temp = (struct node*)malloc(sizeof(struct node));
    temp->data = c;
    temp->next = top;
    top = temp;
}
char pop() 
{
    struct node *temp = top;
    char data = temp->data;
    top = top->next;
    free(temp);
    return data;
}

当前警告:

stack.c: In function âmainâ:
stack.c:24:3: warning: format â%sâ expects argument of type âchar *â, but argument 3 has type âchar **â [-Wformat]
stack.c:26:3: warning: passing argument 1 of âstrcmpâ from incompatible pointer type [enabled by default]
/usr/include/string.h:143:12: note: expected âconst char *â but argument is of type âchar **â
stack.c:31:4: warning: format â%sâ expects argument of type âchar *â, but argument 3 has type âchar **â [-Wformat]
stack.c:32:4: warning: passing argument 1 of âstrcmpâ from incompatible pointer type [enabled by default]
/usr/include/string.h:143:12: note: expected âconst char *â but argument is of type âchar **â
stack.c:35:5: warning: format â%sâ expects argument of type âchar *â, but argument 3 has type âchar **â [-Wformat]
stack.c:39:3: warning: passing argument 1 of âstrcmpâ from incompatible pointer type [enabled by default]
/usr/include/string.h:143:12: note: expected âconst char *â but argument is of type âchar **â
stack.c:42:4: warning: format â%sâ expects argument of type âchar *â, but argument 3 has type âchar **â [-Wformat]
stack.c:43:4: warning: passing argument 1 of âstrcmpâ from incompatible pointer type [enabled by default]
/usr/include/string.h:143:12: note: expected âconst char *â but argument is of type âchar **â

Answer 1

警告已经告诉您该怎么做。函数期望的指针char*和传递的指针&p1也就是char**是不同类型的。要解决这个问题，你必须使用p1而不是&p1。

但是你有另一个问题，你使用p1之前，它被初始化。这也会导致分段错误，因为指针不指向任何地方，而printf或strcmp函数试图访问那里的内容。

这意味着在fscanf的情况下，您必须分配内存，可以存储内容，参见malloc。当然，p2也是如此。

Answer 2

首先，p1没有任何内存可以指向。其次，您将&p1传递给fscanf，但fscanf期望它是char *，而&p1是char **，因为您已将其配置为char *p1和char *p2。我建议你从头开始编写代码，而不是复制代码，因为这段代码有很多错误。可能你的分割错误是由于fscanf()本身，因为你传递的参数是write类型。