Where can I find the full C++ documentation?

Many tutorials and a lot of documentation about UE4 deals with blueprints. Only few articles deals about C++. I would like to use blueprints, but I suppose that they have a bad performance because they are interpreted by a VM.
Please, don’t tell me that I should download the source from Github and read each header.

The API reference is available online at:

or, you can access it from the help menu in the editor.