CODEWITHSUNDEEP
c++pointersstdvector
Alexey S. Larionov
Alexey S. Larionov

Reputation: 7927

Vector of pointers to possibly nonexistent objects

I have an object A, that I want to wrap with a list of objects (pointers to objects) of type B, that A should process.

The problem is, that some of B objects can be deleted and A doesn't know about it. I know I can handle it with exceptions, but I would rather to avoid it.

Full problem: I'm writing C++ SFML project, I want to wrap a sf::RenderWindow with a vector of sf::Drawable * pointers to objects, that window should draw. And problem is the same. Some of sf::Drawable objects may be already deleted, but sf::RenderWindow tries to use it.

I can possibly cancel the idea of wrapping, but if there a good design solution, it would be great.

Upvotes: 2

Views: 73

Answers (2)

Galik
Galik

Reputation: 48635

You can use a std::unique_ptr which will return true or false in an if() statement depending if it has been deleted or not:

// use a std::unique_ptr that will record if its target has been deleted
std::vector<std::unique_ptr<sf::Drawable>> drawables;

// deleting an element

for(auto& drawable: drawables)
{
    if(needs_to_be_deleted(drawable.get()))
        drawable.reset(); // deletes object
}

// process elements

for(auto& drawable: drawables)
{
    if(drawable) // returns false if element is deleted
    {
        // pass by reference or pointer (using get())
        do_something_with_drawable(drawable.get());
    }
}

Upvotes: 2

mksteve
mksteve

Reputation: 13085

You have to ensure memory is not reused, as it will result in undefined behavior if the object is no longer live when you use it.

Create a map for the live objects, and only use value, if it is still in the map

Upvotes: 0

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