Detect date/time format change in Windows

Question

I have an application that's long running (and nearly always displayed) that shows the current time. Currently, if you change the timezone, time format, or language the format doesn't change unless I quit and restart the application. How can I detect when these change so that I can immediately refresh the formatting?

Note that this is native, not managed code (and I can't change that), so anything that's managed-only is right out.

Answer 1

Changing the timezone sends a WM_TIMECHANGE message to all top-level windows, while changing the time format sends a WM_SETTINGCHANGE message. Changing the language (system locale) requires a reboot and so doesn't send a message.