c - 尝试释放链接列表时出现 SIGABRT

Question

我正在研究教授给我们的一些旧课本，为即将到来的考试做准备，我遇到了这个问题。

我的任务是从结构如下的文本文件中读取信息:

[十进制数字],[罗马数字(字符串)],[o 或 u(优化或未优化的罗马数字)]

几千行并将该信息存储在二叉搜索树中，使用十进制数作为键。每个分支还必须包含该数字出现的次数以及遇到的各种罗马版本的列表，优化后的版本位于列表顶部。然后释放一切。

我的代码(c 语言):

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

struct list //list node
{
  char *rom;
  struct list *next;
};

struct branch //main tree branch
{
  int count, dec;
  struct list *list;
  struct branch *right, *left;
};

struct list *insertnode(struct list *head, char *rom, char opt) //creates a head or creates and adds a new node to the end
{
  struct list *new;
  if(!head) //if !head, make one
    {
      new = malloc(sizeof(new));
      new->rom = malloc(sizeof(char)*(strlen(rom)+1));
      strcpy(new->rom, rom);
      new->next = NULL;
      return new;
    }
  if(opt == 'o') //if the roman form is optimized, put it in front of all the others
    {
      new = malloc(sizeof(new));
      new->rom = malloc(sizeof(char)*(strlen(rom)+1));
      strcpy(new->rom, rom);
      new->next = head;
      return new;
    }
  head->next = insertnode(head->next, rom, opt); //recursive insertions
  return head;
}

struct branch *insertbranch(struct branch *root, int dec, char *rom, char opt) //creates a root or creates and adds a new branch
{
  struct branch *new;
  if(!root) //if !root, make a root...
    {
      new = malloc(sizeof(new));
      new->list = insertnode(new->list, rom, opt);
      new->dec = dec;
      new->count = 1;
      new->right=new->left=NULL;
      return new;
    }
  if(dec<root->dec) root->left = insertbranch(root->left, dec, rom, opt); //branch on the left, recursive
  else if(dec>root->dec) root->right = insertbranch(root->right, dec, rom, opt); //branch on the right, recursive
  else //if there already is such a branch, increase its count
    {
      root->count += 1;
      root->list = insertnode(root->list, rom, opt);
    }
  return root;
}

void freelist(struct list *head) //frees list 'head'
{
  struct list *tmp;
  while(head)
    {
      tmp = head;
      head = head->next;
      free(tmp->rom);
      free(tmp); // <- OFFENDING LINE
    }
  return;
}

void freetree(struct branch *root) //frees tree 'root'
{
  if(!root) return;
  freetree(root->left); //recursive!
  freetree(root->right); //and on the right
  free(root->right);
  free(root->left);
  freelist(root->list);
  free(root);
  return;
}

int main()
{
  struct branch *root;
  struct list *list;
  int dec, i=1, n;
  char rom[30], opt;
  FILE *file = fopen("rom.csv", "r");
  if(!file) //is the file even there?
    return 1;

  while(fscanf(file, "%d,%[^,],%c\n", &dec, rom, &opt)==3) //go through the file and fill tree
    root = insertbranch(root, dec, rom, opt);

  freetree(root);
  printf("Goodbye!\n");
  return 0;
}

调试后我隔离了问题:在函数“freelist”中，当它到达命令“free(tmp)”时，程序中止。我不知道原因是什么。我什至检查以确保节点头存在。

感谢您的帮助!

Answer 1

您没有在 insertnode() 和 insertbranch() 中分配正确的内存量。

您需要替换它:

new = malloc(sizeof(new));

与:

new = malloc(sizeof(*new));

这是因为new是一个指针。使用malloc(sizeof(new))，您仅分配空间来存储指针，而不是存储结构内容所需的空间。

以下是这些函数的正确版本:

struct list *insertnode(struct list *head, char *rom, char opt) //creates a head or creates and adds a new node to the end
{
    struct list *new;
    if(!head) //if !head, make one
    {
        new = malloc(sizeof(*new));
        new->rom = malloc(sizeof(char)*(strlen(rom)+1));
        strcpy(new->rom, rom);
        new->next = NULL;
        return new;
    }
    if(opt == 'o') //if the roman form is optimized, put it in front of all the others
    {
        new = malloc(sizeof(*new));
        new->rom = malloc(sizeof(char)*(strlen(rom)+1));
        strcpy(new->rom, rom);
        new->next = head;
        return new;
    }
    head->next = insertnode(head->next, rom, opt); //recursive insertions
    return head;
}

struct branch *insertbranch(struct branch *root, int dec, char *rom, char opt) //creates a root or creates and adds a new branch
{
    struct branch *new;
    if(!root) //if !root, make a root...
    {
        new = malloc(sizeof(*new));
        new->list = insertnode(new->list, rom, opt);
        new->dec = dec;
        new->count = 1;
        new->right=new->left=NULL;
        return new;
    }
    if(dec<root->dec) root->left = insertbranch(root->left, dec, rom, opt); //branch on the left, recursive
    else if(dec>root->dec) root->right = insertbranch(root->right, dec, rom, opt); //branch on the right, recursive
    else //if there already is such a branch, increase its count
    {
        root->count += 1;
        root->list = insertnode(root->list, rom, opt);
    }
    return root;
}

我没有仔细查看每一行代码，但看起来大部分都是正确的。从我的快速浏览来看，您唯一的错误是分配的内存少于您使用的内存。写入过去分配的内存的结果是不可预测的，并且可能会在程序中稍后出现(例如释放内存时)。这就是为什么未定义的行为很难调试:)