问题描述
我目前正在研究CS50x问题集5，Speller。使用valgrind时，出现以下错误：
==395== Memcheck,a memory error detector
==395== copyright (C) 2002-2017,and GNU GPL'd,by Julian Seward et al.
==395== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==395== Command: ./speller texts/cat.txt
==395==
==395==
==395== Process terminating with default action of signal 11 (SIGSEGV)
==395== Bad permissions for mapped region at address 0x601DE8
==395== at 0x401155: add_Node (dictionary.c:75)
==395== by 0x401239: load (dictionary.c:107)
==395== by 0x400944: main (speller.c:40)
==395==
==395== HEAP SUMMARY:
==395== in use at exit: 5,328,336 bytes in 95,140 blocks
==395== total heap usage: 95,141 allocs,1 frees,5,332,432 bytes allocated
==395==
==395== 552 bytes in 1 blocks are still reachable in loss record 1 of 2
==395== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==395== by 0x5258E49: __fopen_internal (iofopen.c:65)
==395== by 0x5258E49: fopen@@GLIBC_2.2.5 (iofopen.c:89)
==395== by 0x4011BE: load (dictionary.c:88)
==395== by 0x400944: main (speller.c:40)
==395==
==395== 5,327,784 bytes in 95,139 blocks are still reachable in loss record 2 of 2
==395== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==395== by 0x401118: add_Node (dictionary.c:69)
==395== by 0x401239: load (dictionary.c:107)
==395== by 0x400944: main (speller.c:40)
==395==
==395== LEAK SUMMARY:
==395== definitely lost: 0 bytes in 0 blocks
==395== indirectly lost: 0 bytes in 0 blocks
==395== possibly lost: 0 bytes in 0 blocks
==395== still reachable: 5,140 blocks
==395== suppressed: 0 bytes in 0 blocks
==395==
==395== For counts of detected and suppressed errors,rerun with: -v
==395== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Segmentation fault
// Loads dictionary into memory,returning true if successful else false
bool load(const char *dictionary)
{
FILE *file = fopen(dictionary,"r");
if (file == NULL)
{
return false;
}
// Set pointers in table to NULL
for (int i = 0; i < N; i++)
{
table[i] = NULL;
}
char word[LENGTH + 1]; //to hold a word from dictionary
while (fgets(word,LENGTH + 1,file) != NULL)
{
int row = hash(word); // to determine where to store the word
add_Node(row,word);
}
fclose(file);
return true;
}
// Adds new node to a list in dictionary
void add_Node(int row,char word[LENGTH + 1])
{
node *newNode = malloc(sizeof(node));
strcpy(newNode->word,word);
if (table[row] == NULL) //if single linked list is empty
{
table[row] = newNode;
}
else
{
node *tmpHead = table[row];
table[row] = newNode;
newNode->next = tmpHead;
}
}
第89行对应于：
add_Node(row,word);
第105行对应于“ table [row] = newNode;”。在：
if (table[row] == NULL) //if single linked list is empty
{
table[row] = newNode;
}
table是一个全局变量，是节点类型的指针数组。我已经验证了该行肯定在数组table的范围内。我不知道如何解决此问题。可能是什么问题？
解决方法
首先，因为您没有阅读while (fgets(word,LENGTH + 1,file) != NULL)，所以请使用将while(fscanf(file,"%s",word) != EOF)更改为"\n"。
您的add_Node函数缺少某些行，需要进行一些更改：
旧版本：
// Adds new node to a list in dictionary
void add_Node(int row,char word[LENGTH + 1])
{
node *newNode = malloc(sizeof(node));
strcpy(newNode->word,word);
if (table[row] == NULL) //if single linked list is empty
{
table[row] = newNode;
}
else
{
node *tmpHead = table[row];
table[row] = newNode;
newNode->next = tmpHead;
}
}
新：
// Adds new node to a list in dictionary
void add_Node(int row,char word[LENGTH + 1])
{
node *newNode = malloc(sizeof(node));
//Test if the node is not empty
if(newNode == NULL){
return 1;
}
strcpy(newNode->word,word);
newNode->next = NULL;
if (table[row] == NULL) //if single linked list is empty
{
table[row] = newNode;
}
else
{ //Set the newNode to table at row and make table[row]
//equal to newNode to overwrite the current address at table[row].
//No need for tmp as we are not swapping things.
newNode -> next = table[row];
table[row] = newNode;
}
}
这应该可以解决您的valgrind问题。另外，您不需要tmp节点，因为这不是必需的。我不确定您的hash函数是否运作良好，但我认为可以。最后，在fclose(file)函数末尾使用load，因为根据valgrind的说法，这将导致“可达”内存泄漏。