Debugger Throwing nullptr Exception During nullptr Check

Question

While going through runtime, I'm getting a nullptr exception while this code is executing.

bool Tree::Insert(int n)
{
    if (root == nullptr) // This is where it throws
    {
        Node* root = new Node(n);
        return true;
    }

Initialization in Tree.h

private:
Node* root;

and Tree constructor.

Tree::Tree()
{
    root = nullptr;
}

I have coded exactly like this before and it never threw an exception.

UPDATE: I apologize for the confusion on the extra '}' Tree::Insert(). There's more code in there and they all have a return case. I had this before

Node* newNode = new Node(n);
root = newNode;

but changed it for a different reason.

Node.h

#pragma once

struct Node
{
    int data;
    Node *left;
    Node *right;

    // Constructor
    Node() { data = 0; left = nullptr; right = nullptr; }
    // Parameterized
    Node(int d) { data = d; left = nullptr; right = nullptr; }
    // Destructor
    ~Node() { data = 0; }
};

Please provide a minimal, complete and verifiable example: https://stackoverflow.com/help/mcve — The Quantum Physicist, Mar 17 '17 at 08:41
Not all paths return in `Tree::Insert`, it's undefined behavior — Danh, Mar 17 '17 at 08:42
BTW You're defining a new `root` variable inside a new Scope, shadowing the class variable. — pinkfloydx33, Mar 17 '17 at 08:42

Dmitry Egorov · Accepted Answer · 2017-03-17T08:57:12.520

2

You either access the Tree::Insert member directly (i.e. not via an instance of the Tree class as if it was a static member) or the instance of the Tree class you're using to access the Insert method is not initialized.

In other words, this is null.

edited Mar 17 '17 at 08:57

answered Mar 17 '17 at 08:44

Dmitry Egorov

9,542
3
22
40

@TobySpeight, exactly! This is what I was typing when noticed your comment. – Dmitry Egorov Mar 17 '17 at 08:58
I'm such an idiot. The issue was in my driver. rather then properly initializing it by typing "Tree* Binary_Tree = new Tree;" I instead typed "Tree* Binary_Tree;" Because of this, the constructor wasn't called. – Daniel Espinel Mar 17 '17 at 09:01

score -2 · Answer 2 · answered Mar 17 '17 at 09:04

-2

nullptr is implementation-specific. when you say, "I have coded exactly like this before and it never threw an exception." you may have to check if it was on a different compiler.

answered Mar 17 '17 at 09:04

venki

35
6

`nullptr` is not implementation-specific an any meaningful sense here. `nullptr_t::operator==` is fully specified in the standard. – Toby Speight Mar 17 '17 at 09:37

Debugger Throwing nullptr Exception During nullptr Check

2 Answers2