Switch over a non-enumerator value for an enum class

alexey_r_9204 0
Viewed 35

In C++ it's allowed to have values of an enumeration type which don't correspond to any enumerator so long as they are in range:

enum class E { X = 1, Y = 2 };

E z = static_cast<E>(0);

Is it possible to switch over such a value? That is,

void f(E a) {
    switch(a) {
    case E::X:  // something
    case E::Y:  // something else
    // somehow check if it's the same as z
    default:    // something else again
    }
}

I expect it isn't, but wanted to confirm, and will be quite happy if it is.

The unsatisfactory options I know:

switch(static_cast<int>(a)) {
case 1:  // something
case 2:  // something else
case 0:  // the z case
default: // something else again
}

or

if (a == E::X) {
    // something
} else if (a == E::Y) {
    // something else
} else if (static_cast<int>(a) == 0)
    // the z case
} else {
    // something else again
}
enums c++
1 Answers

This should do:

enum class E { X = 1, Y = 2 };

constexpr E z = static_cast<E>(0);

void f(E a) {
  switch (a) {
    case E::X:  // ...
    case E::Y:  // ...
    case z:     // ...
    default:    // ...
  };
}
user_101473990
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