Error when trying to include cuchar in Xcode 6.3

I'm having a problem using #include <cuchar> in my C++ program. When I use that line, I get the error

Lexical or Preprocessor Error 'cuchar' file not found.

I've tried setting my project to GNU C++ 11, C++ 11, GNU C++ 14, and C++ 14. Any advice would be appreciated.