Pset5 Trie Segmentation fault

Question

Have been trying to debug this for days and eventually came down to the following problem: When running an example test(lalaland.txt) the misspelled words are fine up until the program abruptly stops(in this case between line 4311 and 4328 of the given text). The error is a segmentation fault, have researched a lot, but still can't find what I did wrong. Here's my code:

 // Implements a dictionary's functionality

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "dictionary.h"

// Represents number of children for each node in a trie
#define N 27

// Represents a node in a trie
typedef struct node
{
    bool is_word;
    struct node *children[N];
}
node;

// Represents a trie
node *root;

// Word counter variable
int counter = 0;
// Loads dictionary into memory, returning true if successful else false

bool load(const char *dictionary)
{

    // Initialize trie
    root = malloc(sizeof(node));
    if (root == NULL)
    {
        return false;
    }
    root->is_word = false;
    for (int i = 0; i < N; i++)
    {
        root->children[i] = NULL;
    }

    // Open dictionary
    FILE *file = fopen(dictionary, "r");
    if (file == NULL)
    {
        unload();
        return false;
    }


    node *dict = root;
    // Insert words into trie
    while (true)
    {
        char word = fgetc(file);
        if(word == EOF)
        {
            break;
        }
        if(word != '\n')
        {
           int index = (word >= 'a' && word <= 'z') ? word - 'a' : 26;
            if (dict->children[index] == NULL)
            {
                dict->children[index] = malloc(sizeof(node));
                dict->children[index]->is_word = false;
                dict = dict->children[index];
                for (int j = 0; j < N; j++)
                {
                    dict->children[j] = NULL;
                }
            }else{
                dict = dict->children[index];
            }
        }else{
            dict->is_word = true;
            dict = root;
            counter++;
        }

    }

    // 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)
{
    if (!counter)
    {
        return counter;
    }
    return 0;
}

// Returns true if word is in dictionary else false

bool check(const char *word)
{
    node *dict = root;
    for (int i = 0; i < strlen(word); i++)
    {
        int index = 0;
        if (word[i] == '\'')
        {
            index = 26;
        }else{
            if (word[i] >= 'a' && word[i] <= 'z')
            {
                index = word[i] - 'a';
            }else{
                if(word[i] >= 'A' && word[i] <= 'Z'){
                    index = word[i] - 'A';
                }else{
                    return false;
                }
            }
        }
        if (dict->children[index] != NULL)
        {
            dict = dict->children[index];
        }else{
            return false;
        }
    }
    return dict->is_word;
}


//stores current node
node *curr;
// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
    if (root == NULL)
    {
        return false;
    }
    node* child[N];
    //initializing children
    for(int i = 0; i < N; i++)
    {
        child[i] = curr->children[i];
    }
    //remove current node
    free(curr);
    //recursion over all children
    for(int i = 0; i < 27; i++)
    {
        if(child[i] != NULL)
        {
            curr = child[i];
        }

        unload();
    }
    return true;
}

Answer 1

It could be because you're looking in the wrong place. The code is seg faulting in the unload() function. Specifically, it fails at this line:

    child[i] = curr->children[i];

The seg fault happens because curr is uninitialized.

Also, why does unload() call itself recursively at the end, with no mechanism to terminate?

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