Applying a rule on how to increment an enum

Question

Is there a way to change how an enum sets the values of its constants? Normally it's incrementing by one but I want to apply an other rule. In PAWN this would work

enum (<<=1) {
 a = 1,//0b001
 b,//0b010
 c//0b100
}

Is there a way to do this in C++?

Answer 1

not automatically, but you can specify manually each value

enum X {
  a = 0x01,
  b = 0x02,
  c = 0x04
};

Answer 2

You could automate this shifting process using templates metaprogramming:

template<int by>
struct OneShlBy {
    enum { Value = OneShlBy<by - 1>::Value << 1 };
};

template<>
struct OneShlBy<0> {
    enum { Value = 1 };
};

enum X {
    a = OneShlBy<0>::Value,
    b = OneShlBy<1>::Value,
    c = OneShlBy<2>::Value
};