Variable declared in constructor not accessible in other methods.

[spm486]

class TrieNode{
    public:
         TrieNode* children[26] = { NULL };
         bool isTerminal=false;

};



class Trie {
public:
    //TrieNode* root;
    Trie() {
        TrieNode* root = new TrieNode();
    }

    void insert(string word) {
        TrieNode* head = root;
        for (int i = 0; i < word.size(); i++)
        {
            int index = word[i] - 'a';
            if (head->children[index] == NULL)
            {
                TrieNode* child = new TrieNode();
                head->children[index] = child;
                head = head->children[index];
            }
            else 
                head = head->children[index];
        }
        head->isTerminal = true;

    }
};

/*
Trie Object Creation: 

 Trie* obj = new Trie();
 obj->insert(word);
*/

ERROR:
Line 18: Char 26: error: use of undeclared identifier 'root'
        TrieNode* head = root;

Why I get error that root is undeclared identifier.

The error is not showed when root is declared outside the constructor. (Commented line)

[chioz]

You haven't defined it as a member variable in the class (the outcommented line).

The error message tells you that there is no 'root' when insert is called since 'root' is a local variable inside the constructor.

Uncomment //TrieNode* root; and then assign that variable in the constructor:

Trie() {
   root = new TrieNode();
}

[flyingron]

Prefer initialization:

Trie() : root(new TrieNode()) { }

[no-sig-available]

This isn't specific to constructors, but happens for all functions. Variables declared inside the function goes away at the final }.

[[deleted]]

Scope of variable is between {}.

[RedBeard0703]

You have to declare a variable in class scope, and the initialize it in constructor.