MessageBox not show before function

[A Former User]

QMessageBox box;
box.setTitle("title");
box.show;
//other stuff

I want to show message box to inform user. I do not want to use exec() because user has to click. I just want to show message while function is working.
But with this code messageBox appear after function. How can I open messageBox before function without using exec()

[mrjj]

-But with this code messageBox appear after function

But box is deleted when function ends so im not sure
how it can be shown after?

Can you show the real code?