c - 两位数指针？这怎么发生的？

Question

所以在我正在处理的项目中，我遇到了以下错误:

*** glibc detected *** ./social_network: munmap_chunk(): invalid pointer: 0x09a913b0 ***

一些 printf 语句揭示了导致此错误的我正在释放的结构的内存地址为....17。那么这怎么可能呢？发生了什么事使这看起来......？

这是崩溃前的一些输出:

temp is: 162075592
temp user is  162075408
After free of temp
inside while loop, first line
before free of temp
temp is: 162075760
temp user is  162075480
After free of temp
inside while loop, first line
before free of temp
temp is: 162075568
temp user is  17

这是输出输出的代码

 21 void destroy() {
 22 
 23     struct user_node *node;
 24 
 25     struct friend_node *temp;
 26     struct friend_node *next_temp;
 27     
 28     //iterate over the list of users
 29     while (*head != NULL) {
 30         printf("before a_friend\n");
 31         temp = (*head)->a_friend;
 32         
 33         //Iterate over friends of users, free friend nodes
 34         while (temp != NULL) {
 35             printf("inside while loop, first line\n");
 36             next_temp = temp->next_friend;
 37             printf("before free of temp\n");
 38             printf("temp is: %d\n", (int) temp);
 39             printf("temp user is  %d\n", (int)temp->user);
 40             free(temp); <==================================SEGFAULT IS HERE!!!!!!!!!!!!!
 41             printf("After free of temp\n");
 42             temp = next_temp;
 43             next_temp = NULL;
 44         }
 45 
 46         node = (*head)->next_user;
 47         printf("before free of: %s\n", (*head)->name);
 48         free(*head);
 49         printf("after free of that person...\n");
 50         *head = node;
 51         printf("*head = node afterwards\n");
 52         node = NULL;
 53     }
 54     printf("before final free...\n");
 55     free(head);
 56 }

编辑:

构造 friend 节点

 23 //node used to store a pointer to a user_node and next friend
 24 struct friend_node {
 25     struct friend_node *next_friend;
 26     struct user_node *user;
 27 }; 

结构用户节点

 12 //Struct definitions
 13 //node used to store information about a user
 14 struct user_node {
 15     char name[21];
 16     int age;
 17     int gender;
 18     char location[21];
 19     struct friend_node *a_friend;
 20     struct user_node *next_user;
 21 };
 22    

Answer 1

这通常发生在您使用 NULL 指针时。你看，当你访问一个结构的成员时，它的偏移量被添加到指针然后被取消引用:

somestruct *p = NULL;
printf("%d", p->member);

如果成员处于偏移状态，例如0xC，那么你将不会收到类似“试图访问 0x0 处的内存”的错误，而是“尝试访问 0xC 处的内存”。

编辑:正如其他人所建议的，这可能不是您遇到问题的原因。但这是在“两位数指针”处收到错误的常见原因。