Returning a pointer to a vector element

Question

I'm trying to figure out best way to hold a pointer to an element in a vector that has just been created and added to the member variable vector:

  SceneGraphNode* addChild(std::string name){
    SceneGraphNode child(this,name);
    m_children.push_back(child);
    return &child;
}

The compiler rightfully gives me a warning since I am returning the address of an object created on the stack, and that object will go out of scope as the function ends. However, the object lives on in the vector, right?

So, should I ignore the warning or is there a better way to do this?

Answer 1

However, the object lives on in the vector, right?

No, a copy of it does. You want to return the address of the copy.

return &m_children.back();

However, it is not a good idea to store a pointer to an object that resides in a vector. Because when the vector needs to reallocate, the pointer will be invalidated. Perhaps you should store pointers (preferably smart pointers) in your vector instead.

For example:

// in your class
std::vector<std::unique_ptr<SceneGraphNode>> m_children;

SceneGraphNode* addChild(std::string name)
{
    std::unique_ptr<SceneGraphNode> child(new SceneGraphNode(this,name));
    m_children.push_back(std::move(child));
    return m_children.back().get();
}