Loading a trie data structure in C- pset5 cs50 - c

Question

I am having trouble loading data into my trie structure. I keep getting a sgemenation fault. Does this have to do with my malloc? Anyone see any issues?
Thanks
/**
* dictionary.c
*
* Computer Science 50
* Problem Set 5
*
* Implements a dictionary's functionality.
*/
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include "dictionary.h"
#define ASCII_OFFSET 97;
/** Node of the data structure used to store the dictionary key words
* Data Structures Type is Tries
* Includes a bool to indicate if the current node is the end of a word
* A pointer to the nodes child node
*/
typedef struct node
{
bool is_word;
struct node* children[27];
}
node;
node* rootNode;
node* nextNode;
//Variable to track the size of the dictinoary
int wordCount = 0;
/**
* Returns true if word is in dictionary else false.
*/
bool check(const char* word)
{
//Get words length
int wordLength = strlen(word);
for(int i = 0; i < wordLength; i++)
{
//taking the character we need to check
int charToCheck = tolower(word[i]) - ASCII_OFFSET;
//Checking to see if the char exists in the data strucutre, Trie;
if(nextNode->children[charToCheck] == NULL)
{
return false;
}
//Advance the next node down the trie
nextNode = nextNode->children[charToCheck];
}
nextNode = rootNode;
//Return what is_word return
return nextNode->is_word;
}
/**
* Loads dictionary into memory. Returns true if successful else false.
*/
bool load(const char* dictionary)
{
//Open dict.. file to read
FILE* file = fopen(dictionary,"r");
//Check if the dict.. exsists!
if(file == NULL)
{
return false;
}
//Creating the first node in our data strucutre
rootNode = malloc(sizeof(node));
nextNode = rootNode;
//Get character to store
int character = fgetc(file) - ASCII_OFFSET;
//Go through the dict... file
while(character != EOF)
{
//Go through each word in the file
while(character != '\n')
{
//Add into our data structure
if(nextNode->children[character] == NULL)
{
//Create memory inorder to insert the next node
nextNode->children[character] = malloc(sizeof(node));
nextNode = nextNode->children[character];
}else {
nextNode = nextNode->children[character];
}
//advance character to next
character = fgetc(file) - ASCII_OFFSET;
}
//advance character to next word
character = fgetc(file) - ASCII_OFFSET;
//Set the last node loaded to is_word to track the end of each word
nextNode->is_word = true;
wordCount++;
nextNode = rootNode;
}
fclose(file);
return true;
}
/**
* Returns number of words in dictionary if loaded else 0 if not yet loaded.
*/
unsigned int size(void)
{
return wordCount;
}
/**
* Unloads dictionary from memory. Returns true if successful else false.
*/
bool unload(void)
{
for(int i = 0; i < 26; i++)
{
if(nextNode->children[i] != NULL)
{
nextNode = nextNode->children[i];
unload();
}
}
free(nextNode);
return true;
}

Answer 1

You don't check that a char is in range before using it as index in the array. Any character outside the range a-z will cause buffer overflow.
You compare the character to known character constants after you have subtracted 97 from it.
You need to initialize the memory returned from malloc by assigning NULL to all array elements and set is_word to false.
Just took a short glance at the code, so I may have missed additional bugs.