c - 拼写器 cs50 中的分段错误
问题描述
目前,我正在研究 pset5,每当我尝试编译时,都会遇到分段错误。我找不到错误所在,非常感谢专家的帮助。暗示错误是完全可以的。
代码:
// Implements a dictionary's functionality
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include "dictionary.h"
int word_count = 0;
// 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 = 27;
// Hash table
node *table[N];
// Returns true if word is in dictionary else false
bool check(const char *word)
{
// Converting word to lower case
char *lower_word = NULL;
strcpy(lower_word, word);
int len = 0;
len = sizeof(lower_word);
for (int i = 0; i < len; i++)
{
lower_word[i] = tolower(lower_word[i]);
}
node *head = NULL;
node * cursor = NULL;
cursor = head;
while (cursor != NULL)
{
cursor = head;
if (cursor -> word == lower_word)
{
return true;
}
else
{
cursor = cursor -> next;
}
}
return false;
}
// Hashes word to a number
unsigned int hash(const char *word)
{
// TODO
// From: http://www.cse.yorku.ca/~oz/hash.html
unsigned long sdbm(char *word);
{
unsigned long hash = 0;
int c;
while ((c = *word++))
{
hash = c + (hash << 6) + (hash << 16) - hash;
// Deleted free(word);
}
return hash;
}
return 0;
}
// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
// Opening the file
FILE *dict = fopen(dictionary, "r");
if (dict == NULL)
{
return false;
}
// Read strings from file
char word[LENGTH + 1];
for (int i = 0; i < N; i++)
{
table[i] = NULL;
}
while (fscanf(dict, "%s", word) == EOF)
{
// Create a new node
node *n = malloc(sizeof(node));
n -> next = NULL;
if (n == NULL)
{
return 1;
}
// Insert word into node
int x = hash(word);
strcpy(n -> word, word);
// Set position x in table equal to node
if(table[x] == NULL)
{
table[x] = n;
}
else
{
n = table[x];
table[x] = n;
}
// Count word for size function
word_count++;
}
fclose(dict);
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
// TODO
int table_size = 0;
table_size = sizeof(table)/sizeof(table[0]);
int count = 0;
for (int i = 0; i < table_size; i++)
{
count++;
}
return count;
return 0;
}
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
// TODO
int table_size = 0;
table_size = sizeof(table)/sizeof(table[0]);
node *cursor = NULL;
node* tmp = NULL;
for (int i = 0; i < table_size; i++)
{
while (cursor != NULL)
{
tmp = cursor;
cursor = cursor -> next;
free(tmp);
}
}
return true;
}
输入:
./speller texts/lalaland.txt
输出:
MISSPELLED WORDS
Segmentation fault
有人遇到过 CS50 pset5 吗?如需更多信息,请参阅:https ://cs50.harvard.edu/x/2020/psets/5/speller/
我看过很多次演练,也看过短裤,但我没有进步。
更新检查功能:
{
// Hash word to obtainhash value
int bucket = hash(word);
// Traverse linked list and look for the word using strcmp
node *cursor = NULL;
node *head = table[bucket];
cursor = head;
while (cursor != NULL)
{
if (strcasecmp(cursor -> word, word) == 0)
{
return true;
}
else
{
cursor = cursor -> next;
}
}
return false;
}
更新2:
// Implements a dictionary's functionality
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>
#include <ctype.h>
#include "dictionary.h"
#define HASHMAX 1000
int word_count = 0;
// 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 = 143091;
// Hash table
node *table[N];
// Returns true if word is in dictionary else false
bool check(const char *word)
{
// Hash word to obtainhash value
int bucket = hash(word);
// Traverse linked list and look for the word using strcmp
node *cursor = NULL;
node *head = table[bucket];
cursor = head;
while (cursor != NULL)
{
if (strcasecmp(cursor -> word, word) == 0)
{
return true;
}
else
{
cursor = cursor -> next;
}
}
return false;
}
// Hashes word to a number
unsigned int hash(const char *word)
{
// TODO
// From: http://www.cse.yorku.ca/~oz/hash.html
unsigned long sdbm(char *word);
{
unsigned long hash = 5381;
int c;
while ((c = *word++))
{
hash = c + (hash << 6) + (hash << 16) - hash;
// Deleted free(word);
}
return hash % HASHMAX;
}
return 0;
}
// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
// Opening the file
FILE *dict = fopen(dictionary, "r");
if (dict == NULL)
{
return false;
}
// Read strings from file
char word[LENGTH + 1];
for (int i = 0; i < N; i++)
{
table[i] = NULL;
}
while (fscanf(dict, "%s", word) != EOF)
{
// Create a new node
node *n = malloc(sizeof(node));
n -> next = NULL;
if (n == NULL)
{
return 1;
}
// Insert word into node
int x = hash(word);
strcpy(n -> word, word);
// Set position x in table equal to node
if(table[x] == NULL)
{
table[x] = n;
}
else
{
n = table[x];
table[x] = n;
}
// free(n);
// Count word for size function
word_count++;
}
fclose(dict);
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
// TODO
int table_size = sizeof(table)/sizeof(table[0]);
int count = 0;
for (int i = 0; i < table_size; i++)
{
count++;
}
return count;
return 0;
}
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
// TODO
int table_size = sizeof(table)/sizeof(table[0]);
node *cursor = NULL;
node* tmp = NULL;
for (int i = 0; i < table_size; i++)
{
node *head = table[i];
while (cursor != NULL)
{
tmp = cursor;
cursor = cursor -> next;
free(tmp);
}
}
return true;
}
结果:
WORDS MISSPELLED: 17263
WORDS IN DICTIONARY: 143091
WORDS IN TEXT: 17756
TIME IN load: 0.02
TIME IN check: 0.01
TIME IN size: 0.00
TIME IN unload: 0.00
TIME IN TOTAL: 0.03
解决方案
错误的近因:NULL 是一个常数,这意味着它不能被改变,这一行char *lower_word = NULL;
设置lower_word
为 NULL,这一行strcpy(lower_word, word);
试图改变它。段错误。
也许考虑简单地迭代单词并将每个字符设置为“就地”降低。
编辑后:
table
分配给 N (27) 个元素。该hash
函数返回的值WAY大于 27。您可以将哈希函数更改为简单的字母索引(类似于tolower(word[i]) - 'a'
)或使用模 ( %
) 运算符来限制存储桶大小。
这些可能不是程序中唯一的问题,但当然需要修复 seg 错误才能取得真正的进展。debug50
是你的朋友(和小字典一起使用更容易!)
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