Elaborated-type-specifier for a scoped enum must not use the ‘class’ keyword

问题

I have the following enum specification:

enum class FaceDirection : int8
{
  Down,
  Up
};

g++ 4.8.1 gives the following error:

warning: elaborated-type-specifier for a scoped enum must not use the ‘class’ keyword

What causes this?

回答1:

Check the type you are deriving the enum class from exists. In this case, there was no typedef specified for int8.

来源：https://stackoverflow.com/questions/20459120/elaborated-type-specifier-for-a-scoped-enum-must-not-use-the-class-keyword