Does anyone know of a standalone software (or plugin for Visual Studio) that can generate UML class diagrams from C++ code?
Take a look at DoxyGen.
It is widely used in industry . If you add specially formatted comments to your code, it can generate some very useful documentation. in fact the first thing I do on every new contract is to run the code through Doxygen.
In fact, even without the comments, it still gives a great deal of information, such as call trees, class diagrams and the like.
Read about its diagrams here
And read the S.O question How to use doxygen to create UML class diagrams from C++ source
Visual Studio 2017 (Community Edition), and later versions, have a Class Designer component for generating class diagrams. Follow the setup instructions by Microsoft in this article for installing the Class Designer component.
Once installed, open your Visual Studio project, right-click on a header file and select the "View Class Diagram" option.
Caveat: The Class Designer feature only works with Visual Studio project files (i.e.
*.vcxproj). You won't be able to use this feature if you have a CMake project. Check this post on Visual Studio's developer community for further info.