一段时间以来，我一直在使用此字典的“拼写检查”功能，并最终使其完全正常运行，除了一个小错误，即不知道该内存泄漏在哪里。当我运行valgrind时会出现：
> ==793== Memcheck, a memory error detector
> ==793== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
> ==793== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
> ==793== Command: ./speller texts/cat.txt
> ==793==
>
> MISSPELLED WORDS
>
> ==793== Conditional jump or move depends on uninitialised value(s)
> ==793== at 0x520A60F: tolower (ctype.c:46)
> ==793== by 0x4010E2: check (dictionary.c:37)
> ==793== by 0x400CD9: main (speller.c:112)
> ==793== Uninitialised value was created by a stack allocation
> ==793== at 0x4008E4: main (speller.c:21)
> ==793==
> ==793== Use of uninitialised value of size 8
> ==793== at 0x520A623: tolower (ctype.c:46)
> ==793== by 0x4010E2: check (dictionary.c:37)
> ==793== by 0x400CD9: main (speller.c:112)
> ==793== Uninitialised value was created by a stack allocation
> ==793== at 0x4008E4: main (speller.c:21)
> ==793==
>
> WORDS MISSPELLED: 0 WORDS IN DICTIONARY: 143091 WORDS IN TEXT:
> 6 TIME IN load: 1.44 TIME IN check: 0.05 TIME IN size:
> 0.00 TIME IN unload: 0.19 TIME IN TOTAL: 1.69
>
> ==793==
> ==793== HEAP SUMMARY:
> ==793== in use at exit: 552 bytes in 1 blocks
> ==793== total heap usage: 143,096 allocs, 143,095 frees, 8,023,416 bytes allocated
> ==793==
> ==793== 552 bytes in 1 blocks are still reachable in loss record 1 of 1
> ==793== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==793== by 0x5258E49: __fopen_internal (iofopen.c:65)
> ==793== by 0x5258E49: fopen@@GLIBC_2.2.5 (iofopen.c:89)
> ==793== by 0x401211: load (dictionary.c:77)
> ==793== by 0x4009B4: main (speller.c:40)
> ==793==
> ==793== LEAK SUMMARY:
> ==793== definitely lost: 0 bytes in 0 blocks
> ==793== indirectly lost: 0 bytes in 0 blocks
> ==793== possibly lost: 0 bytes in 0 blocks
> ==793== still reachable: 552 bytes in 1 blocks
> ==793== suppressed: 0 bytes in 0 blocks
> ==793==
> ==793== For counts of detected and suppressed errors, rerun with: -v
> ==793== ERROR SUMMARY: 8 errors from 2 contexts (suppressed: 0 from 0)
很抱歉发布整个内存消息，但是我不确定Valgrind消息的哪一部分有错误的位置。
下面是发生错误的C代码，我假设它在加载或卸载函数中。
```C
//for the universal hash function
#define BASE 256
// 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 = 676;
// Hash table
node *table[N];
int word_count = 0;
// Returns true if word is in dictionary else false
//Require a search funtion
bool check(const char *word)
{
//change to lower case to compare
char low[LENGTH + 1];
for (int i = 0, n = strlen(word); i <= (n + 1); i++)
{
low[i] = tolower(word[i]);
}
int hashIndex = hash(low);
for (node *tmp = table[hashIndex]; tmp != NULL; tmp = tmp->next)
{
if (strcasecmp(low, tmp->word) == 0)
{
return true;
}
}
return false;
}
// Hashes word to a number
// the dividing hash function is one I cited from the yale.edu page http://www.cs.yale.edu/homes/aspnes/pinewiki/C(2f)HashTables.html having worked with.
unsigned int hash(const char *word)
{
unsigned long m = 11;
unsigned long h;
unsigned const char *us;
//ensure element value is >= 0
us = (unsigned const char *) word;
h = 0;
while(*us != '\0')
{
h = (h * BASE + *us) % m;
us++;
}
return (h % N);
}
// Loads dictionary into memory, returning true if successful else false
//Bring the used sictionary to menu asap
bool load(const char *dictionary)
{
// Open file and check file
FILE *file = fopen(dictionary, "r");
if (!file)
{
return false;
}
//array declaration for fscanf to read into
char word[LENGTH + 1];
while (fscanf(file, "%s", word) == 1)
{
//Create node n = new node
node *n = malloc(sizeof(node));
if (n == NULL)
{
printf("No memory for node\n");
fclose(file);
return false;
}
strcpy(n->word, word);
//Hash the word
int hashDigit = hash(word);
//Insert into the beginning of the list
if (table[hashDigit] == NULL)
{
table[hashDigit] = n;
n->next = NULL;
}
else
{
n->next = table[hashDigit];
table[hashDigit] = n;
}
word_count++;
}
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
//count the amount of words in dictionary
unsigned int size(void)
{
return word_count;
}
// Unloads dictionary from memory, returning true if successful else false
//free the dictionary from memory asap
bool unload(void)
{
//Loop to run through array
for (int i = 0; i < N; i++)
{
//to target linked list
while (table[i] != NULL)
{
node *tmp = table[i];
table[i] = table[i]->next;
free(tmp);
}
}
return true;
}
据我所知，我已经尝试正确地释放了所有的内存，并从第36行的“有条件的跳转或移动取决于未初始化的值”中出现了，但是我不确定这恰好意味着或如何解决该问题。
我希望获得一些有关如何更好地做到这一点的建议。
答案 0 :(得分：3)
它会泄漏您从FILE*获得的fopen。 fclose丢失。
这是valgrind告诉您的地方：
==793== 552 bytes in 1 blocks are still reachable in loss record 1 of 1
==793== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==793== by 0x5258E49: __fopen_internal (iofopen.c:65)
==793== by 0x5258E49: fopen@@GLIBC_2.2.5 (iofopen.c:89)
==793== by 0x401211: load (dictionary.c:77)
==793== by 0x4009B4: main (speller.c:40)
fopen最终调用malloc来分配FILE，它必须与fclose一起释放，而free最终在该FILE*上调用Conditional jump or move depends on uninitialised value。 / p>
for (int i = 0, n = strlen(word); i <= (n + 1); i++)
low[i] = tolower(word[i]);
警告是由以下原因引起的：
i <= n该循环从零终止符处读取一个额外的字符。它需要修复：i < (n + 1)或a = 1。
答案 1 :(得分：2)
> ==793== 552 bytes in 1 blocks are still reachable in loss record 1 of 1
> ==793== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==793== by 0x5258E49: __fopen_internal (iofopen.c:65)
> ==793== by 0x5258E49: fopen@@GLIBC_2.2.5 (iofopen.c:89)
> ==793== by 0x401211: load (dictionary.c:77)
> ==793== by 0x4009B4: main (speller.c:40)
泄漏是来自fopen，因为您没有打电话给fclose。
答案 2 :(得分：0)
您在此处创建了大量指针
node *table[N];
但是您永远不要将该数组设置为NULL。
然后，假设该数组已初始化，您可以对该数组进行各种处理。
答案 3 :(得分：0)
我遇到了同样的问题（哈佛 CS50 课程第 5 周），但上面的答案只让我成功了一半。
最终通过将空终止符 '\0' 显式分配给每个单词的剩余字符来解决它，如下所示：
for (int i = 0; i < LENGTH + 1; i++) {
low[i] = (i < strlen(word)) ? tolower(word[i]) : '\0';
}