Adding words to a trie - c++

Question

I am creating a trie and am having trouble at the time of compiling.
The warningI get is:
"Reading invalid data from 'currNode->dict': the readable size is '104' bytes, but '388' bytes may be read."
#pragma once
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
const int SIZE = 26;
struct Node {
bool isWord;
Node* dict[SIZE];
};
class Dictionary
{
public:
Dictionary();
Dictionary(string file);
void addWord(string word);
private:
Node *root;
int numWords;
};
Dictionary::Dictionary()
{
numWords = 0;
root = new Node;
for (int i = 0; i < SIZE; i++)
root->dict[i] = nullptr;
}
Dictionary::Dictionary(string file)
{
numWords = 0;
root = new Node;
for (int i = 0; i < SIZE; i++)
root->dict[i] = nullptr;
ifstream inFile;
string word;
inFile.open(file);
while (inFile >> word) {
addWord(word);
numWords++;
}
}
void Dictionary::addWord(string word)
{
int len = word.length(); // size of word
char letter;
int pos;
Node *currNode = root;
for (int i = 0; i < len; i++) {
letter = word[i]; // takes character at position i
pos = letter - 'a'; // finds the position of the character in the array (0 through 25)
// with 'a' being 0 and 'z' being 25
if (!currNode->dict[pos]) {
currNode->dict[pos] = new Node;
currNode->isWord = false;
}
currNode = currNode->dict[pos];
}
currNode->isWord = true;
}
What could be causing this? I'm pretty sure that I'm not trying to access invalid memory. Perhaps it's the way I setup my node and class?

Answer 1

One mistake is that you fail to initialize Node to default values. In your Dictionary default constructor, you have code that really should be part of what Node should be doing:
root = new Node ;
for (int i = 0; i < SIZE; i++)
root->dict[i] = nullptr;
This should be Node's job, not the job of Dictionary.
Instead, you have this:
struct Node {
bool isWord;
Node* dict[SIZE];
};
So every time you do this:
if (!currNode->dict[pos]) {
currNode->dict[pos] = new Node;
You are creating an uninitialized Node object. That entire Node::dict array contains uninitialized pointers, which you later try to access.
The easiest solution is to zero-initialize the Node object.
if (!currNode->dict[pos]) {
currNode->dict[pos] = new Node(); // <-- Note the parentheses
This will automatically set the dict pointers to nullptr.
The other method is to make sure Node objects are created with default values:
#include <algorithm>
struct Node {
bool isWord;
Node* dict[SIZE];
Node() : isWord(false) { std::fill_n(dict, SIZE, nullptr); }
};
With this, even new Node; will create nodes that are initialized.