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I am making an RPG game with C++/x86 asm. My question is related to the C++ component. In C++/win32 how would I detect if the computer is shutting down or turning off, or whatever else - so that I can save the game session. My game has a 'save' option, but if the user or another program decides to shut off the computer how can I detect this with some kind of API hook so that I can instantly save the game session to the text file.

Now please don't suggest an option by creating a thread to run passively as I want to keep the file size to a minimum, so if you can suggest some sort of WM_ hook that would be great. I'd refer to MSDN but I don't want to be searching for hours through their WM directory.

Peter O.
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You can handle session saving in response to the WM_ENDSESSION message. Note that after your message handler returns from handling this, your process may be terminated at any time, so you need to save it directly during the message handler, and not just set a flag to let some later code handle the saving, because that later code might not get to execute.

A comment suggests the WM_QUERYENDSESSION message. This has a slightly different meaning: it gives applications the chance to complain about the session ending, and gives the user a chance to not log off / shut down the system. Based on your question, you have no intention of preventing any such thing, so WM_ENDSESSION seems like a better match to me.

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    It may be wise to prepare the file contents at `WM_QUERYENDSESSION` already as shutdown should be a quick process. – MSalters Jul 21 '14 at 07:14