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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;
}
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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?

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)

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  • Thanks for the help, you are a saviour :) – IVO PETROV Sep 21 '19 at 14:12

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