What is LRESULT? How do I use it?

[jojobear99]

I am using a message map with a custom ON_MESSAGE handler. The callback function called by the message handler requres the return type to be LRESULT, but I am not clear on understanding what I should return in the LRSULT, and how the return value is used.

my callback function called by the ON_MESSAGE call in the message map calls a function like:
LRESULT ClassName::CallbackFunction(WPARAM wParam, LPARAM lParam);
and I have found many examples online that return "LRESULT(true)" from this function, but little explanation of why return true. Could I/Should I return other values ever? What does this return value get used for?

MSDN's explanation that LRESULT is the "Signed result of message processing." and is typdef'd from LONG_PTR doesn't give me the insight I was hoping for. Thanks for your help!

[Quell]

It depends on what you are trying to do, but if you are using it from ON_MESSAGE the returned values usually doesn't matter. return 0L; should do fine.

[hoxsiew]

If you are using a custom message, then Quell's advice is OK, but if you are handing a message normally handled by the default windows proc, then you should return TRUE to indicate that you handled the message and the default proc need not bother; otherwise, the default windows proc will still process it and could override anything you already did.

[a1ex07]

You should read what Windows expects for each message you want to handle. For some of them it expects 0, for others - something else.