当我使用check50时，我的程序没有给出任何报告作为输出。所以我用小字典试了一下代码，结果出现了分段错误。我认为这与我的卸载功能有关这是我的代码
// Implements a dictionary's functionality
#include <stdbool.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include <ctype.h>
#include "dictionary.h"
// Represents a node in a hash table
typedef struct node
{
char word[LENGTH + 1];
struct node *next;
}
node;
// Number of buckets in hash table
const unsigned int N = 125;
int word_size = 0;
// Hash table
node *hashtable[N];
// Returns true if word is in dictionary else false
bool check(const char *word)
{
//Convert the word to lowercase
int length = strlen(word);
char copy[length + 1];
for (int i = 0; i < length; i++)
{
copy[i] = tolower(word[i]);
}
copy[length] = ' ';
//Find out the hash value
int hash_value = hash(copy);
node *tmp = hashtable[hash_value];
//Check if word is in dictionary
while(tmp != NULL)
{
if(strcasecmp(tmp->word, copy) == 0)
{
return true;
}
tmp = tmp->next;
}
return false;
}
// Hashes word to a number
unsigned int hash(const char *word)
{
//It's djb2 hash function
unsigned int hash = 5381;
int c;
while ((c = *word++))
hash = ((hash << 5) + hash) + c;
return hash % N;
}
// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
//Initialize all indexs of hastable to NULL
for(int i =0; i < LENGTH + 1; i++)
{
hashtable[i] = NULL;
}
char word[LENGTH +1];
int pos;
FILE *dict = fopen(dictionary,"r");
if(dict == NULL)
{
return false;
}
//Scan every word...I think my problem is in here
while (fscanf(dict, "%s", word) != EOF)
{
word_size++;
int length = strlen(word);
char copy[length + 1];
for (int i = 0; i < length; i++)
{
copy[i] = tolower(word[i]);
}
copy[length] = ' ';
node *new_node = malloc(sizeof(node));
strcpy(new_node->word,copy);
new_node->next = NULL;
//Find the hash value
pos = hash(copy);
//Set the pointer of the new node to index of hashtable
new_node->next = hashtable[pos];
hashtable[pos] = new_node;
}
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
return word_size;
}
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
node *cursor = NULL;
node* tmp = NULL;
for(int i=0; i < N; i++)
{
while(cursor->next != NULL)
{
tmp = cursor;
cursor = cursor->next;
free(tmp);
}
free(cursor);
}
return true;
}
如果我的卸载函数出错，有人能说出写逻辑吗。它与大字典配合使用很好。我试过了，但不知道如何使用debug50
在unload ()函数中，您很快就定义了
node *cursor = NULL;
但是，在不为cursor分配任何其他值的情况下，您可以取消引用它：
while ( cursor->next != NULL )
取消引用NULL指针会引发未定义的行为，并且很可能会导致分段错误。
下面的操作是带有NULL指针的free(cursor);，这也不好。