I'm working on Speller with a hashtable, and my code compiles, but when I run valgrind it tells me that I'm trying to use an uninitialized value.
==10864== Conditional jump or move depends on uninitialised value(s)
==10864== at 0x40131F: check (dictionary.c:103)
==10864== by 0x400CC9: main (speller.c:112)
==10864== Uninitialised value was created by a heap allocation
==10864== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10864== by 0x40115B: load (dictionary.c:59)
==10864== by 0x4009A4: main (speller.c:40)
==10864==
This error is located in my check function which looks like this (I marked the line with the error code with <-):
bool check(const char *word)
{
// TODO
int len = strlen(word);
char *l = malloc(len + 1);
for (int i = 0; i < len; i++)
{
l[i] = tolower(word[i]);
}
l[len] = '\0';
int bucket = hash(l);
node *cursor = hashtable[bucket];
while (cursor != NULL)<-
{
if (strcasecmp(cursor->word, l) != 0)
{
cursor = cursor->next;
}
else
{
free(l);
return true;
}
}
free(l);
return false;
}
Why does this happen? Shouldn't l have been assigned a value again before reaching that line?
If needed, my whole code looks like this:
// Implements a dictionary's functionality
#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <strings.h>
#include "dictionary.h"
// Represents number of buckets in a hash table
#define N 26
// Represents a node in a hash table
typedef struct node
{
char word[LENGTH + 1];
struct node *next;
}
node;
// Represents a hash table
node *hashtable[N];
int val = 0;
// Hashes word to a number between 0 and 25, inclusive, based on its first letter
unsigned int hash(const char *word)
{
return tolower(word[0]) - 'a';
}
// Loads dictionary into memory, returning true if successful else false
bool load(const char *dictionary)
{
// Initialize hash table
for (int i = 0; i < N; i++)
{
hashtable[i] = NULL;
}
// Open dictionary
FILE *file = fopen(dictionary, "r");
if (file == NULL)
{
unload();
return false;
}
// Buffer for a word
char buf[LENGTH + 1];
// Insert words into hash table
while (fscanf(file, "%s", buf) != EOF)
{
// TODO
node *temp_node = malloc(sizeof(node));
strncpy(temp_node->word, buf, sizeof(buf));
int s = hash(buf);
if (hashtable[s] == NULL)
{
hashtable[s] = temp_node;
}
else
{
temp_node->next = hashtable[s];
hashtable[s] = temp_node;
}
val++;
}
// Close dictionary
fclose(file);
// Indicate success
return true;
}
// Returns number of words in dictionary if loaded else 0 if not yet loaded
unsigned int size(void)
{
// TODO
return val;
}
// Returns true if word is in dictionary else false
bool check(const char *word)
{
// TODO
int len = strlen(word);
char *l = malloc(len + 1);
for (int i = 0; i < len; i++)
{
l[i] = tolower(word[i]);
}
l[len] = '\0';
int bucket = hash(l);
node *cursor = hashtable[bucket];
while (cursor != NULL)
{
if (strcasecmp(cursor->word, l) != 0)
{
cursor = cursor->next;
}
else
{
free(l);
return true;
}
}
free(l);
return false;
}
void destruct(node *head)
{
if (head->next != NULL)
{
destruct(head->next);
}
free(head);
}
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
// TODO
for (int i = 0; i < N; i++)
{
if (hashtable[i] != NULL)
{
destruct(hashtable[i]);
}
}
return true;
}
xat line 102. And for the record, these are warnings, but there is no memory leak, at least when I tested.