Question

I am looking for a way to pass an object (vector<long> in my case) as a WPARAM in C++11 style.

The tutorials I found used a C-style cast or a reinterpret_cast to pass a pointer to the object. This requires that the recipient of the message properly disposes the object after receiving it.

Is there a way to pass the object using a unique_ptr? The recipient can take full ownership of the object.

Answer 1

If you pass a pointer to an object with a windows message then you need to ensure 2 things:

1. The source doesn’t destroy the object before the message has been handled
2. The destination correctly destroys the object if necessary

If you know that the message will definitely be handled then you can call .release() on the source unique_ptr when sending the message, and then take ownership in the handler with another unique_ptr.

The problem comes with ensuring it is cleaned up if the message is NOT handled. This is tricky, as there isn’t usually a clean way to check unless you use SendMessage (not PostMessage) and use the return value to communicate that the parameter has been claimed.