In my last question (Qt/C++: Icons not showing up when program is run) I asked how to get an icon to show up on a toolbar and was told I needed a Qt Resource, which I added and that fixed my problem, the icon did show up on the toolbar.
Now I’m trying to set the title icon of a window, using the same resource file, and it shows up fine in the Qt preview viewer but blank in the actual program. I am using a MainWindow which has an MDIArea and the children are MainWindows as well; neither the parent MDI nor child MDI windows icons will show properly. On the parent, I see the regular “Windows Application icon” and on the child, the icon is completely blank.

How can I solve this?
You will have to go through a standard resource file for windows. (That is, a .rc)
The process (as described in the documentation) is:
In the Visual Studio case you’re simply able to add a resource to your project.