How frameworks like Qt create GUI, if C++ has no functionality for that?

Question

From the answers recieved for the question here: Graphics using Standard C++ only?

Seems to be that C++ itself does not have GUI functionality. So how do other Frameworks like Qt which support GUI in C++ do that? Do they use some other language internally or is there some other standard lobrary/protocol for GUI?

And I am concerned about the C++ language frameworks only.

Thank You.

Answer 1

They call operating system APIs, or APIs in other frameworks, in order to create GUI components.

Eg. on Windows they call the Windows CreateWindow API to create a window.

Where a framework works on multiple platforms, it contains different GUI code for each of those platforms, calling CreateWindow on Windows or whatever the Mac equivalent is on a Mac, for example.