Windows property "SIZE ON DISK" How to get this size by qt C++ [duplicate]

I have a question on window folder property. When I'm checking property it's shows two size that is size and disk on size. So whenever I'm using qfileinfo it's show only size of folder. But i need "Size on disk". So what's is the method to get size on disk. And please explain that why is happening.

Help me for this.

Thanks in advance.

I want to check size on disk by qt C++ language