c - 为什么在尝试填充结构时出现段错误(核心转储)或总线错误(核心转储)？

Question

所以我尝试使用指向 MonsterAttacks 结构的指针作为属于链表元素的数据。为了做到这一点，我尝试填充一个 MonsterAttacks 结构，然后将它与一个 null ptr 一起传递到下一个节点到一个名为 create 的函数。然而，在 populate 方法的某处发生了段错误。我正在处理三个文件 list_demo.c、linked_list.h 和 linked_list.c。我将构建构成功能齐全的链表的所有函数，希望我能尽快通过此错误。处理这个错误大约两天了，我给我的教授看了，他不明白为什么会这样，它似乎来自 populate 函数。我试图返回一个指向 strut 的指针，在这种情况下我得到一个总线错误，并且我已经尝试了几乎所有获取输入并将其存储在 strut 上的变体。我什至删除了该函数并尝试将其填充到 main 中，但没有任何效果。我是 C 的新手，我的教授帮助我调试了大约一个小时，但他最终放弃了，所以任何帮助都将不胜感激。

list_demo.c

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



 void populate(struct MonsterAttacks *m){

    printf("Enter the name for the Monster \n");
    scanf("%40s",m->monsterName);
    puts("What is his/her attack location?");
    scanf("%40s",m->attackLocation);
    puts("What are the number of victims this monster has demolished?");
    scanf("%ud", &m->numOfVictims);      
    m->attackID = 0;
}

int main(void)
{

   node* tmp = NULL;
   struct MonsterAttacks *tmpMonst = (struct MonsterAttacks *) 
   malloc(sizeof(struct MonsterAttacks));

   if(tmpMonst == NULL){
      printf("Error allocating memory");
   }
   else
      populate(tmpMonst);

   node *head = create(tmpMonst,tmp);

   free(tmpMonst);
   return 0;
}

linked_list.h

#ifndef LINKED_LIST
#define LINKED_LIST


typedef struct node{
   struct MonsterAttacks *monsterAttack;
   struct node* next;
} node;


struct MonsterAttacks{
   unsigned int attackID;
   char monsterName[41];
   char attackLocation[41];
   unsigned int numOfVictims;
};

/*
   create a new node
   initialize the data and next field

   return the newly created node
*/
node* create(struct MonsterAttacks *m,node* next);



#endif

linked_list.c

//来自zentut.com，大量改编

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "linked_list.h" 


/*
   create a new node
   initialize the data and next field
   return the newly created node
*/
node* create(struct MonsterAttacks *m,node* next)
{
    node* new_node = (node*)malloc(sizeof(node));
    if(new_node == NULL)
    {
        printf("Error creating a new node.\n");
        exit(0);
    }

     new_node->monsterAttack->attackID = 0;

     new_node->next = next;

     strncpy(new_node->monsterAttack->monsterName,m->monsterName,41);
     strncpy(new_node->monsterAttack->attackLocation, m->attackLocation, 41);
     new_node->monsterAttack->numOfVictims = m->numOfVictims;

      return new_node;
}

顺便说一句，使用 gcc 编译器在 Red Hat 上运行

Answer 1

new_node->monsterAttack->attackID = 0;

为 new_node 分配内存不会为其内部的 MonsterAttacks 结构分配内存。这就是为什么取消引用 monsterAttack 以获取其 attackID 会导致段错误。

一个最小的工作代码

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
// Moved the two structs out to make a minimal reproducible code
/*  #include "linked_list.h" */

struct MonsterAttacks{
    unsigned int attackID;
    char monsterName[41];
    char attackLocation[41];
    unsigned int numOfVictims;
};

typedef struct node{
    struct MonsterAttacks *monsterAttack;
    struct node* next;
} node;

void populate(struct MonsterAttacks *m){

    printf("Enter the name for the Monster \n");
    scanf("%40s",m->monsterName);
    puts("What is his/her attack location?");
    scanf("%40s",m->attackLocation);
    puts("What are the number of victims this monster has demolished?");
    scanf("%ud", &m->numOfVictims);      
    m->attackID = 0;
}

node* create(struct MonsterAttacks *m,node* next)
{
    node* new_node = (node*)malloc(sizeof(node));
    if(new_node == NULL)
    {
        printf("Error creating a new node.\n");
        exit(0);
    }

    // Just add this line
    new_node->monsterAttack = malloc(sizeof (struct MonsterAttacks));

    new_node->monsterAttack->attackID = 0;
    new_node->next = next;

    strncpy(new_node->monsterAttack->monsterName,m->monsterName,41);
    strncpy(new_node->monsterAttack->attackLocation, m->attackLocation, 41);
    new_node->monsterAttack->numOfVictims = m->numOfVictims;

    return new_node;
}

int main(void)
{
    node* tmp = NULL;
    struct MonsterAttacks *tmpMonst = (struct MonsterAttacks *) 
        malloc(sizeof(struct MonsterAttacks));

    if(tmpMonst == NULL){
        printf("Error allocating memory");
    }
    else {
        populate(tmpMonst);
    }

    node *head = create(tmpMonst,tmp);

    printf("Name: %s\n", tmpMonst->monsterName);
    printf("num victim: %d\n", tmpMonst->numOfVictims);

    free(tmpMonst);
    return 0;
}

当您在 create(...) 中为 new_node 分配内存时，您在堆上为 node 类型的结构分配内存保存它包含的所有变量。在这种情况下，node 中的 monsterAttack 最初是一个指向无处可去的结构的指针。您需要为要指向的 monsterAttack 指针显式分配内存。