当我运行 Valgrind 时，我的代码中出现大小为 8 的无效写入错误答案

【问题标题】：I am getting an error of invalid write of size 8 on my code when I run Valgrind当我运行 Valgrind 时，我的代码中出现大小为 8 的无效写入错误
【发布时间】：2020-08-02 03:08:01
【问题描述】：

我也收到了来自 Valgrind 的这条消息。

valgrind: m_mallocfree.c:280 (mk_plain_bszB): Assertion 'bszB != 0' failed.
valgrind: This is probably caused by your program erroneously writing past the
end of a heap block and corrupting heap metadata.  If you fix any
invalid writes reported by Memcheck, this assertion failure will
probably go away.  Please try that before reporting this as a bug.

如果有人可以测试，这是我的代码

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

//creating the node structure
typedef struct node
{
    char first_name[45];
    struct node *next_node;
}
node;

int main(void)
{
    // creating the pointer list and setting it to NULL;
    node *list = NULL;
    char name[20];
    // creating the first node
    node *n = malloc(sizeof(n));
    if(n == NULL)
    {
        printf("malloc cound't get enough mem.\n");
        return 1;
    }
    // dereferencing the name in node and the next_node pointer in n
    printf("Please print the users first name\n");
    // getting user input and storing it in first name
    scanf("%s",n->first_name);

    n->next_node = NULL;
    // having list point at n the first node
    list = n;
    // creating the tempory pointer we will use to make the linked list in a loop
    node *temp = NULL;

    // generating a singly linked list with a loop
    for(int i = 0; i < 7; i++)
    {
        temp = n;
        n = malloc(sizeof(node));
        if(n == NULL)
        {
            printf("malloc wasn't able to allocate the memory we needed. Aborting the program\n");
            return 1;
        }
        //dereferencing the new n node
        printf("Please print the users first name\n");
        // getting user input on the name and storing it in the first name array
        scanf("%s",n->first_name);
        n->next_node = temp;
        list = n;
    }

    // looping through the linked list and printing out the values
    for(node*tmp = list; tmp!=NULL;tmp=tmp->next_node)
    {
        printf("The name of the user is %s\n",tmp->first_name);

    }
    // freeing the linked list
    while(list!=NULL)
    {
        node *tempr = list->next_node;
        free(list);
        list = tempr;
    }

}

我不知道如何解决这个错误。如果有人可以提供帮助，我将不胜感激。

【问题讨论】：

使用调试信息构建您的程序。这是 GCC 或 Clang 的 -g 标志。然后 Valgrind 会告诉你你的 bug 到底在哪里。
OT：关于：printf("malloc cound't get enough mem.\n"); 错误消息应该输出到stderr，而不是stdout。当错误来自 C 库函数时，还应输出系统认为发生错误的文本原因。建议：perror("malloc could't get enough mem."); 作为函数：perror() 用于处理这两个活动

标签： c memory valgrind

【解决方案1】：

node *n = malloc(sizeof(n));

您正在使用指针大小作为参数保留空间（肯定不是您想要的），以使用 struct 本身的大小保留空间：

node *n = malloc(sizeof(*n));

或

node *n = malloc(sizeof(node));

正如您在 for 循环中所做的那样。

【讨论】：