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I'm working on a code which is supposed to load a dictionary and check if the words in a text is correct.
The code compiles when working with small lists (for dictionary) yet I get 'segmentation error: core dumped' when I run it with large lists.
I checked if there is a memory leak with valgrind and apparently there is in line where I defined tmp. (node *tmp = malloc(sizeof(node))).
I tried to fixing the error by adding freeing memory for node *tmp by adding free(tmp) in different lines of code. But the end result is mostly dictionary loading incorrectly.
Below is the code.
// Implements a dictionary's functionality
#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cs50.h>
#include <strings.h>
#include "dictionary.h"
// Represents a node in a hash table
typedef struct node
{
char word[LENGTH + 1];
struct node *next;
} node;
// TODO: Choose number of buckets in hash table
const unsigned int N = 26;
// Hash table
node *table[N];
// Returns true if word is in dictionary, else false
bool check(const char *word) // this is from another file which works fine.
{
int hash_value = hash(word);
node *table_tmp = table[hash_value];
for(node *ptr = table_tmp; ptr != NULL; ptr = ptr->next)
{
if (strcasecmp(ptr->word, word))
{
return true;
}
}
return false;
}
// Hashes word to a number
unsigned int hash(const char word[LENGTH + 1])
{
return toupper(word[0]) - 'A';
}
// Loads dictionary into memory, returning true if successful, else false
bool load(const char *dictionary)
{
// Opens the dictionary
FILE *source = fopen(dictionary, "r");
if (source == NULL)
{
fclose(source);
return 0;
}
char word_read[LENGTH + 1];
// Reads data
while (fgets(word_read, sizeof(word_read), source) != NULL)
{
unsigned int hash_value = hash(word_read);
node *tmp = malloc(sizeof(node));
if (tmp == NULL)
{
return 1;
}
strcpy(tmp->word, word_read);
tmp->next = NULL;
// Appends with tmp if table is empty
if (table[hash_value] == NULL)
{
table[hash_value] = tmp;
}
// Appends with tmp itaretively using ptr pointer
else
{
for(node *ptr = table[hash_value]; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
ptr->next = tmp;
break;
}
}
}
for(node *ptr = tmp; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
break;
}
free(ptr);
ptr = NULL;
}
}
if (size() != 0)
{
return true;
}
else
{
return false;
}
}
// Returns number of words in dictionary if loaded, else 0 if not yet loaded
unsigned int size(void)
{
int counter = 0;
for(int i = 0; i < N; i++)
{
for(node *ptr = table[i]; ptr != NULL; ptr = ptr->next)
{
counter++;
if (ptr->next == NULL)
{
break;
}
}
}
if (counter == 0)
{
return 0;
}
return counter;
}
// Unloads dictionary from memory, returning true if successful, else false
bool unload(void)
{
for(int i = 0; i < N; i++)
{
for(node *ptr = table[i]; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
break;
}
free(ptr);
}
}
for(int i = 0; i < N; i++)
{
if (table[i] != NULL)
{
table[i] = NULL;
}
}
for(int i = 0; i < N; i++)
{
if (table[i] != NULL)
{
return false;
}
}
return true;
}
When I run valgrind check, below is the output.
It's apparent that the memory lead is coming from not freeing node *tmp, but I need help on how I should do that.
Also, I appreciate any feedback on the implementation of the for loop (maybe that's the underlying reason behind having the memory issue).
`==10230==
==10230== HEAP SUMMARY:
==10230== in use at exit: 696 bytes in 5 blocks
==10230== total heap usage: 12 allocs, 7 frees, 10,552 bytes allocated
==10230==
==10230== 224 bytes in 4 blocks are definitely lost in loss record 1 of 2
==10230== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==10230== by 0x109A36: load (dictionary.c:67)
==10230== by 0x1092CB: main (speller.c:40)
==10230==
==10230== 472 bytes in 1 blocks are still reachable in loss record 2 of 2
==10230== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==10230== by 0x49CEE6E: __fopen_internal (iofopen.c:65)
==10230== by 0x49CEE6E: fopen@@GLIBC_2.2.5 (iofopen.c:86)
==10230== by 0x1099DE: load (dictionary.c:52)
==10230== by 0x1092CB: main (speller.c:40)
==10230==
==10230== LEAK SUMMARY:
==10230== definitely lost: 224 bytes in 4 blocks
==10230== indirectly lost: 0 bytes in 0 blocks
==10230== possibly lost: 0 bytes in 0 blocks
==10230== still reachable: 472 bytes in 1 blocks
==10230== suppressed: 0 bytes in 0 blocks
==10230==
==10230== For lists of detected and suppressed errors, rerun with: -s
==10230== ERROR SUMMARY: 4 errors from 2 contexts (suppressed: 0 from 0)`
I'm working on a code which is supposed to load a dictionary and check if the words in a text is correct.
The code compiles when working with small lists (for dictionary) yet I get 'segmentation error: core dumped' when I run it with large lists.
I checked if there is a memory leak with valgrind and apparently there is in line where I defined tmp. (node *tmp = malloc(sizeof(node))).
I tried to fixing the error by adding freeing memory for node *tmp by adding free(tmp) in different lines of code. But the end result is mostly dictionary loading incorrectly.
Below is the code.
// Implements a dictionary's functionality
#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cs50.h>
#include <strings.h>
#include "dictionary.h"
// Represents a node in a hash table
typedef struct node
{
char word[LENGTH + 1];
struct node *next;
} node;
// TODO: Choose number of buckets in hash table
const unsigned int N = 26;
// Hash table
node *table[N];
// Returns true if word is in dictionary, else false
bool check(const char *word) // this is from another file which works fine.
{
int hash_value = hash(word);
node *table_tmp = table[hash_value];
for(node *ptr = table_tmp; ptr != NULL; ptr = ptr->next)
{
if (strcasecmp(ptr->word, word))
{
return true;
}
}
return false;
}
// Hashes word to a number
unsigned int hash(const char word[LENGTH + 1])
{
return toupper(word[0]) - 'A';
}
// Loads dictionary into memory, returning true if successful, else false
bool load(const char *dictionary)
{
// Opens the dictionary
FILE *source = fopen(dictionary, "r");
if (source == NULL)
{
fclose(source);
return 0;
}
char word_read[LENGTH + 1];
// Reads data
while (fgets(word_read, sizeof(word_read), source) != NULL)
{
unsigned int hash_value = hash(word_read);
node *tmp = malloc(sizeof(node));
if (tmp == NULL)
{
return 1;
}
strcpy(tmp->word, word_read);
tmp->next = NULL;
// Appends with tmp if table is empty
if (table[hash_value] == NULL)
{
table[hash_value] = tmp;
}
// Appends with tmp itaretively using ptr pointer
else
{
for(node *ptr = table[hash_value]; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
ptr->next = tmp;
break;
}
}
}
for(node *ptr = tmp; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
break;
}
free(ptr);
ptr = NULL;
}
}
if (size() != 0)
{
return true;
}
else
{
return false;
}
}
// Returns number of words in dictionary if loaded, else 0 if not yet loaded
unsigned int size(void)
{
int counter = 0;
for(int i = 0; i < N; i++)
{
for(node *ptr = table[i]; ptr != NULL; ptr = ptr->next)
{
counter++;
if (ptr->next == NULL)
{
break;
}
}
}
if (counter == 0)
{
return 0;
}
return counter;
}
// Unloads dictionary from memory, returning true if successful, else false
bool unload(void)
{
for(int i = 0; i < N; i++)
{
for(node *ptr = table[i]; ptr != NULL; ptr = ptr->next)
{
if (ptr->next == NULL)
{
break;
}
free(ptr);
}
}
for(int i = 0; i < N; i++)
{
if (table[i] != NULL)
{
table[i] = NULL;
}
}
for(int i = 0; i < N; i++)
{
if (table[i] != NULL)
{
return false;
}
}
return true;
}
When I run valgrind check, below is the output.
It's apparent that the memory lead is coming from not freeing node *tmp, but I need help on how I should do that.
Also, I appreciate any feedback on the implementation of the for loop (maybe that's the underlying reason behind having the memory issue).
`==10230==
==10230== HEAP SUMMARY:
==10230== in use at exit: 696 bytes in 5 blocks
==10230== total heap usage: 12 allocs, 7 frees, 10,552 bytes allocated
==10230==
==10230== 224 bytes in 4 blocks are definitely lost in loss record 1 of 2
==10230== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==10230== by 0x109A36: load (dictionary.c:67)
==10230== by 0x1092CB: main (speller.c:40)
==10230==
==10230== 472 bytes in 1 blocks are still reachable in loss record 2 of 2
==10230== at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==10230== by 0x49CEE6E: __fopen_internal (iofopen.c:65)
==10230== by 0x49CEE6E: fopen@@GLIBC_2.2.5 (iofopen.c:86)
==10230== by 0x1099DE: load (dictionary.c:52)
==10230== by 0x1092CB: main (speller.c:40)
==10230==
==10230== LEAK SUMMARY:
==10230== definitely lost: 224 bytes in 4 blocks
==10230== indirectly lost: 0 bytes in 0 blocks
==10230== possibly lost: 0 bytes in 0 blocks
==10230== still reachable: 472 bytes in 1 blocks
==10230== suppressed: 0 bytes in 0 blocks
==10230==
==10230== For lists of detected and suppressed errors, rerun with: -s
==10230== ERROR SUMMARY: 4 errors from 2 contexts (suppressed: 0 from 0)`
1 Answer
Reset to default 1Code has at least these problems. If all fixed, may/may not solve OP's woes.
Bad pointer
In unload(), code attempts to access ptr->next after free(ptr);
// vvvvvvvvv ---> bad
for(node *ptr = table[i]; ptr != NULL; ptr = ptr->next) {
if (ptr->next == NULL) {
break;
}
free(ptr);
}
Get the next pointer before free(ptr).
Something like:
node *next;
for(node *ptr = table[i]; ptr != NULL; ptr = next) {
next = ptr->next;
free(ptr);
}
Why keep '\n'?
Better to lop off the potential '\n' at the end of word_read[].
word_read[strcspn(word_read, "\n")] = '\0';
Potential invalid index
toupper(word[0]) - 'A' risks returning a value outside [0...N). Better as
(toupper(word[0]) - 'A')%((unsigned)N)
LENGTH unknown and may be too small
for(node *ptr = tmp; ptr != NULL; ptr = ptr->next)
In load(), for loop unclear. What is attempted here? if (ptr->next == NULL) looks to be always true. Stray code?
Minor: inconsistent types
Why int counter, yet function returns an unsigned?
unsigned int size(void) {
int counter = 0;
...
return counter;
}
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word_readandnodeare defined. Please provide A Minimal Complete Reproducible Example. – David C. Rankin Commented yesterdaystrcpy(tmp->word, word_read);, you have just allocatedtmpviamalloc, but you never intialised the pointerword. – OldBoy Commented yesterdaywordis not a pointer, but an array. Yet good observation. – chux Commented yesterday