c - 实现push和pop的单链表-seg fault

Question

我正在查看一些旧代码以编写一个程序(在 C 中)，该程序创建类似于单链表堆栈的推送和弹出方法。我目前遇到段错误，无法找出问题所在。

任何推送的输入都是单个字符，这是一个输入示例:
推；
推 g
推.
流行
推 -

代码(注释掉了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("%s\n", &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("%s\n",&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* 和您传递的指针 &p1 aka char** 是不同类型的。要解决此问题，您必须使用 p1 而不是 &p1。

但是你还有另一个问题，你在初始化之前使用了p1。这也会导致段错误，因为指针指向任何地方，函数 printf 或 strcmp 试图访问那里的内容。

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