Another vague question!
As gnasher729 said it's plain ISO Standard C++ with partial C++ 11 implementation. That being the case one of my favorite C++ references is <http://en.cppreference.com/w/Main_Page>
As to Xcode use it's built in help system. It provides some very nice utilities for writing, finding and analyzing C, C++, ObjC and ObjC++ code.
If you're looking for something more specific and can't find it continue to do what you're doing here - ask!