（CS50 / pset5 / speller）根据check50和valgrind，我遇到内存泄漏问题。我想我使用的是没有值的变量 [英] (CS50/pset5/speller) I have a memory leak issue, according to check50 and valgrind. I think I'm using a variable that doesn't have a value
问题描述
根据check50和valgrind的说法，我有内存泄漏问题。看来我正在尝试使用一个可能没有值的变量。根据check50，其他所有内容均正常运行，唯一的问题是内存。这是valgrind的错误消息：
I have a memory leak issue, according to check50 and valgrind. It looks like I'm trying to use a variable that might not have a value. Everything else works correctly, according to check50, the only issue is with memory. Here is valgrind's error message:
==3243== Conditional jump or move depends on uninitialised value(s)
==3243== at 0x520A60F: tolower (ctype.c:46)
==3243== by 0x4010CD: check (dictionary.c:36)
==3243== by 0x400CD9: main (speller.c:112)
==3243== Uninitialised value was created by a stack allocation
==3243== at 0x4008E4: main (speller.c:21)
==3243==
==3243== Use of uninitialised value of size 8
==3243== at 0x520A623: tolower (ctype.c:46)
==3243== by 0x4010CD: check (dictionary.c:36)
==3243== by 0x400CD9: main (speller.c:112)
==3243== Uninitialised value was created by a stack allocation
==3243== at 0x4008E4: main (speller.c:21)
==3243==
WORDS MISSPELLED: 0
WORDS IN DICTIONARY: 143091
WORDS IN TEXT: 6
TIME IN load: 1.46
TIME IN check: 0.00
TIME IN size: 0.00
TIME IN unload: 0.21
TIME IN TOTAL: 1.67
==3243==
==3243== HEAP SUMMARY:
==3243== in use at exit: 0 bytes in 0 blocks
==3243== total heap usage: 143,097 allocs, 143,097 frees, 8,023,462 bytes allocated
==3243==
==3243== All heap blocks were freed -- no leaks are possible
==3243==
==3243== For counts of detected and suppressed errors, rerun with: -v
==3243== ERROR SUMMARY: 492 errors from 2 contexts (suppressed: 0 from 0)
Asking for help...
==3243== Conditional jump or move depends on uninitialised value(s)
Looks like you're trying to use a variable that might not have a value? Take a closer look at line 36 of dictionary.c.
这是我的代码（如果您能提供帮助，我会很乐意;））
Here is my code (I would love if you could help ;))
// Implements a dictionary's functionality
#include <stdbool.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>
#include "dictionary.h"
#define HASHTABLE_SIZE 65536
// 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 = HASHTABLE_SIZE;
// Hash table
node *table[N];
unsigned int totalWords = 0;
// Returns true if word is in dictionary else false
bool check(const char *word)
{
//Initialize lower case word
char lcword[LENGTH + 1];
for (int i = 0; i < LENGTH + 1; i++)
lcword[i] = tolower(word[i]);
node *cursor = table[hash(lcword)];
while (cursor != NULL)
{
if (strcasecmp(word, cursor->word) == 0)
{
return true;
}
cursor = cursor->next;
}
return false;
}
// Hashes word to a number
unsigned int hash(const char *word)
{
//https://www.reddit.com/r/cs50/comments/1x6vc8/pset6_trie_vs_hashtable/cf9nlkn/
unsigned int hash_value = 0;
for (int i = 0, n = strlen(word); i < n; i++)
hash_value = (hash_value << 2) ^ word[i];
return hash_value % HASHTABLE_SIZE;
}
// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
FILE *dicfile = fopen(dictionary, "r");
char *word = malloc(LENGTH + 1);
//Check if word is null
if (word == NULL)
return false;
//Check if the fopen function opened a not NULL file
if (dicfile == NULL)
return false;
//Iterate over dictionary until fscanf return EOF (meaning it's the end of the file)
while (fscanf(dicfile, "%s", word) != EOF)
{
//Create a node to store the current word
node *new_node = malloc(sizeof(node));
if (new_node == NULL)
return false;
//Copy the new_node's word into the current word
strcpy(new_node->word, word);
//Get the index (hash the current word and store it in n)
int n = hash(new_node->word);
//Insert the new_node into the linked list
new_node->next = table[n];
table[n] = new_node;
//Add to the total number of words in the text file
totalWords++;
}
fclose(dicfile);
free(word);
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
return totalWords;
}
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
for (int i = 0; i < HASHTABLE_SIZE; i++)
{
node* cursor = table[i];
node* tmp;
while (cursor != NULL)
{
tmp = cursor;
cursor = cursor->next;
free(tmp);
}
free(cursor);
}
return true;
}
如果您想知道，我代码的第36行就是这样的： lcword [i] = tolower（word [i]）;
And if you want to know, line 36 of my code is this one: lcword[i] = tolower(word[i]);
谢谢！
推荐答案
关于：
for (int i = 0; i < LENGTH + 1; i++)
在C中，数组的有效索引范围是 0 ...（array-1中的元素数）注意-1
in C, the valid range of indexes into an array are 0...(number of elements in array-1 ) Note the -1
注意：宏： LENGTH 在发布的代码中未定义。
Note: the macro: LENGTH is not defined anywhere in the posted code.
函数： check（）在发布的代码中实现，但从未调用。
the function: check() is implemented in the posted code, but never called.
关于：
for ( int i = 0, n = strlen(word); i < n; i++)
函数： strlen（）返回 size_t ，因此该语句应为：
The function: strlen() returns a size_t, so the statement should be:
for ( size_t i = 0, n = strlen(word); i < n; i++ )
函数： size（）已实现，但从未实现
The function: size() is implemented but never called.
包含头文件的那些内容未使用是非常糟糕的编程习惯。例如：
it is a very poor programming practice to include header files those contents are not used. for instance:
#include <strings.h>
；
if (dicfile == NULL)
return false;
这应该紧随其后；
FILE *dicfile = fopen(dictionary, "r");
，并且应包含以下语句：
and should include the statement:
perror( "fopen to read dictionary file failed" );
关于：
while (fscanf(dicfile, "%s", word) != EOF)
还有其他原因导致调用 fscanf（）可能会失败。应该检查是否成功。
there are other reasons that a call to fscanf() can fail. Should be checking for success.
％s 输入格式转换说明符可以输入的字符多于数组 word（）。同样，该说明符总是将NUL字节附加到输入。为避免任何缓冲区溢出问题，请始终使用小于缓冲区长度1的修饰符。建议：
the %s input format conversion specifier can input more characters than there are in the array word(). Also, that specifier always appends a NUL byte to the input. To avoid any buffer overflow problems, always use a modifier that 1 less than the length of the buffer. Suggest:
同时（fscanf（dicfile，％; LENGTH s，单词）== 1）
while (fscanf(dicfile, "%" LENGTH "s", word) == 1)
关于您的问题关于内存泄漏：
regarding your question about a memory leak:
发布的代码修改了指针（通过覆盖）在 table [] 中，而无需首先检查是否存在一个活跃的条目。如果在表的散列索引处已经有一个活动条目，则新条目必须在当前条目之后（可能在之前链接）链接，并在同一索引中链接到 table []
The posted code modifies pointers (by overlaying them) in table[] without first checking of there is already an active entry there. If there is an active entry already at the 'hashed' index into the table, then the new entry must be linked after (could be linked before) the current entry, at the same index into table[]
当然，当覆盖活动条目时，结果是内存泄漏。
Of course, when an active entry is overlayed, the result is a memory leak.
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