Say I have such a class:
enum class Flags : char
{
FLAG_1 = 1;
FLAG_2 = 2;
FLAG_3 = 4;
FLAG_4 = 8;
};
Now can I have a variable that has type flags and assign a value 7
for example? Can I do this:
Flags f = Flags::FLAG_1 | Flags::FLAG_2 | Flags::FLAG_3;
or
Flags f = 7;
This question arises because in the enum I have not defined value for 7
.
You need to write your own overloaded operator|
(and presumably operator&
etc.).
Flags operator|(Flags lhs, Flags rhs)
{
return static_cast<Flags>(static_cast<char>(lhs) | static_cast<char>(rhs));
}
Conversion of an integer to an enumeration type (scoped or not) is well-defined as long as the value is within the range of enumeration values (and UB otherwise; [expr.static.cast]/p10). For enums with fixed underlying types (this includes all scoped enums; [dcl.enum]/p5), the range of enumeration values is the same as the range of values of the underlying type ([dcl.enum]/p8). The rules are trickier if the underlying type is not fixed - so don't do it :)
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