Question

i have small doubt regarding the window functions in c++.
what exactly "invalidate()" function do?
what message does it sends?when we need to call this? also what is "update()" function?
is "invalidaterect()" works similar to "invalidate()" function?.

Thanks

Answer 1

CWnd::Invalidate() invalidates the entire client area of a window, which indicates that the area is out of date, and should be repainted. You would typically call this on a control that needs to be redrawn. CWnd::InvalidateRect() invalidates only part of the window.

With the Invalidate functions, the WM_PAINT message will posted [not strictly true; see the comments] to the message queue and handled at some point in the future. CWnd::UpdateWindow() sends (as opposed to posts) a WM_PAINT message, causing the invalidated regions to be redrawn immediately.

Really, this is all in the docs.