CS_? Because everybody hates
Commenter kero claims that it's "easy to fix" the problem with
CS_. You just remove the
CS_ style temporarily, then do the normal
PrintWindow, then restore the
CS_ style. The question is then why
PrintWindow simply doesn't do this.
The question assumes that the described workaround actually works. It may work in limited situations, but it certainly doesn't work in general.
CS_ style is a class style, removing the style affects all windows of that class, not merely the window you are trying to print. Suppose there are two windows of the class running on different threads, and you remove the
CS_ style in anticipation of doing a
PrintWindow. While that's going on, the other window gets a
WM_ message. Since the
CS_ style was temporarily removed, that window will be painting with an incorrectly-clipped DC. Result: Incorrect pixels on the screen.
The proposed workaround doesn't actually work reliably, which means that it probably shouldn't be done at all. (Random reinforcement breeds superstition.)