Question

这是我的代码：

// Implements a dictionary's functionality

#include <stdbool.h>
#include <stdio.h>
#include <cs50.h>
#include <ctype.h>
#include <string.h>
#include <strings.h>
#include <stdlib.h>

#include "dictionary.h"

// Maximum length for a word
#define LENGTH 45

//define struct node
typedef struct node
{
    char word[LENGTH + 1];
    struct node *next;
}
node;

//hash function
unsigned int hash(const char word[LENGTH + 1])
{
    int x = atoi(&word[0]);
    int y;
    if(isupper(word[0]))
    {
        y = (x + 13) % 26;
    }
    if(islower(word[0]))
    {
        y = (x + 7) % 26;
    }
    if(isalpha(word[0]) == 0)
    {
        return 0;
    }
    return y;
}

//make a hash table of linked lists
node* hash_table[26];

// Returns true if word is in dictionary else false
bool check(const char *word)
{
    node *head = hash_table[hash(word)];
    node *cursor = head;
    while (cursor != NULL)
    {
        if (strcasecmp(word, cursor->word) == 0)
        {
            return true;
        }
        cursor = cursor->next;
    }
    return false;
}

// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
    char word[LENGTH + 1];
    FILE *dictionary_file = fopen(dictionary, "r");
    if (dictionary_file == NULL)
    {
        unload ();
        return false;
    }

    while (fscanf(dictionary_file, "%s", word) != EOF)
    {
        //allocate memory for node
        node *new_node = malloc(sizeof(node));
        if (new_node == NULL)
        {
            unload();
            return false;
        }

        //insert node into linked list
        int index = hash(word);
        node *head = hash_table[hash(word)];

        //place word in node
        strcpy(new_node->word, word);

        //connect nodes
        new_node->next = head;
        hash_table[index] = new_node;
        }
    fclose(dictionary_file);
    return true;
}

// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
    int sum = 0;
    if (&load)
    {
        char word[LENGTH + 1];
        const char *dictionary;
        FILE *dictionary_file = fopen(dictionary, "r");
        while (fscanf(dictionary_file, "%s", word) != EOF)
        {
            sum++;
        }
    }
    return sum;
}

// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
    char word[LENGTH + 1];
    node *head = hash_table[hash(word)];
    node *cursor = head;

    while (cursor != NULL)
    {
        node *temp = cursor;
        cursor = cursor->next;
        free(temp);
    }

    if (cursor == NULL)
    {
        return true;
    }
    else
    {
       return false;
    }
}

当我通过GDB运行它时，我收到以下消息，指示分段错误：

Program received signal SIGSEGV, Segmentation fault.
_int_malloc (av=0x7ffff728d760 <main_arena>, bytes=56) at malloc.c:3777
3777    malloc.c: No such file or directory.

这是我键入“ where”时的GDB响应：

#0  _int_malloc (av=0x7ffff728d760 <main_arena>, bytes=56) at malloc.c:3777
#1  0x00007ffff6f4dae0 in __GI___libc_malloc (bytes=56) at malloc.c:2893
#2  0x0000000000422abf in load (dictionary=0x382e332d6e696168 <error: Cannot access memory at address 0x382e332d6e696168>)
    at dictionary.c:66
#3  0x722d72656c69706d in ?? ()
#4  0x61732f62696c2f74 in ?? ()
#5  0x5f72657a6974696e in ?? ()
#6  0x732f6e6f6d6d6f63 in ?? ()
#7  0x72657a6974696e61 in ?? ()
#8  0x632e7367616c665f in ?? ()
#9  0x6165720000000063 in ?? ()
#10 0x0063632e31720064 in ?? ()
#11 0x2828000000000000 in ?? ()
#12 0x5f76625f706d7421 in ?? ()
#13 0x287469427465672e in ?? ()
#14 0x6c00292929786469 in ?? ()
#15 0x6c6f6f742d6d766c in ?? ()

有人知道为什么会出现分段错误吗？当我通过valgrind运行程序时，系统指示没有内存泄漏。有谁知道如何解决这个问题？

Answer 1

load()函数中存在多个问题，但是我不确定它们是否导致分段错误。

您正在呼叫hash(new_node->word)，然后再从word复制到new_node->word。您应该改为对word进行哈希处理。
您实际上从未真正将新节点放入哈希表。将head链接到旧头之后，您需要将其设置为// Loads dictionary into memory, returning true if successful else false bool load(const char *dictionary) { char word[LENGTH + 1]; FILE *dictionary_file = fopen(dictionary, "r"); if (dictionary_file == NULL) { unload (); return false; } while (fscanf(dictionary_file, "%s", word) != EOF) { //allocate memory for node node *new_node = malloc(sizeof(node)); if (new_node == NULL) { unload(); return false; } //insert node into linked list int hashcode = hash(word); node *head = hash_table[hashcode]; //place word in node strcpy(new_node->word, word); //connect nodes new_node->next = head; hash_table[hashcode] = new_node; } fclose(dictionary_file); return true; }，但是哈希表仍指向旧头。

更新的代码：

valgrind

我在您发布的代码中没有看到任何会引起分段错误的内容，因此您可能在未包含的某些其他代码中具有未定义的行为。使用dendy <- lapply(1:100, function1)之类的工具来查找它。

Answer 2

关于：

const char *dictionary;
FILE *dictionary_file = fopen(dictionary, "r");

（可能是段故障的原因）

指针dictionary在传递给fopen()之前未初始化

因此，代码试图从内存中的某个“随机”位置读取一定数量的“随机”字节（直到遇到NUL字节），以尝试获取要打开的文件的名称。

OT：在调用fopen()之类的C库函数时，请始终在调用后检查是否有任何错误。

编译时，请始终启用警告，然后修复这些警告。（对于gcc，至少使用-Wall -Wextra -Wconversion -pedantic -std=gnu11）

C分段故障malloc.c：没有这样的文件或目录

2 个答案: