Qt application - open one process only

I have Qt GUI application which I want that the user will open one only. I want that if the user will click first time on th exe - it will open the application and when he will click it again it will open the first one.

i don't want to do it with QtSingleApplication. I 开发者_StackOverflow社区want to know exacly how to open the GUI on the second time.

Help me please!

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Even if you don't want to, QtSingleApplication is what works. If you want to learn how it is implemented, you can always read the source code.