enum class egg {Small, Medium, Large, Jumbo};
enum class t_shirt {Small, Medium, Large, XLarge};
也可以使用关键字struct代替class，其枚举量的定义域为类，需要使用枚举名来限定枚举量：
egg choice = egg::Large; // the Large enumerator of the egg enum
t_shirt Floyd = t_shirt::Large; // the Large enumerator of the t_shirt enum
有些情况下，常规枚举量将自动转换为整型。但作用域内枚举量不能隐式地转换为整型：
enum egg_old {Small, Medium, Large, Jumbo}; // unscoped
enum class t_shirt {Small, Medium, Large, XLarge};//scoped
egg_old one = Medium; // unscoped
t_shirt rolf = t_shirt::Large; // scoped
int king = one; // implicit type conversion for unscoped
int ring = rolf; // not allowed, no implicit type conversion
if (king < Jumbo) // allowed
std::cout << "Allowed\n";
if (king < t_shirt::Medium) // not allowed
std::cout << "Not allowed\n";
默认情况下，C++11作用域内枚举的底层类型为int。另外，还提供一种语法，可用于做出不同选择：
// underlying type for pizza is short
enum class : short pizza {Small, Medium, Large, XLarge};
:short将底层类型指定为short，底层类型必须为整型。
