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Showing content from https://cplusplus.com/reference/type_traits/is_enum/ below:

class template

<type_traits>

std::is_enum

template <class T> struct is_enum;

Is enum

Trait class that identifies whether T is an enumeration (enum) type.

It inherits from integral_constant as being either true_type or false_type.

Template parameters

T: A type.

Member types Inherited from integral_constant:

Member constants Inherited from integral_constant:
member constant definition value either true or false
Member functions Inherited from integral_constant:

operator bool: Returns value (public member function)

Example

// is_enum example
#include <iostream>
#include <type_traits>

enum A {first,second,third};       // unscoped enum (C-style)
class B {};
enum class C {alpha,beta,gamma};   // scoped enum (C++11-style)

int main() {
  std::cout << std::boolalpha;
  std::cout << "is_enum:" << std::endl;
  std::cout << "A: " << std::is_enum<A>::value << std::endl;
  std::cout << "B: " << std::is_enum<B>::value << std::endl;
  std::cout << "C: " << std::is_enum<C>::value << std::endl;
  std::cout << "decltype(C::alpha): " << std::is_enum<decltype(C::alpha)>::value << std::endl;
  return 0;
}

Output:

is_enum:
A: true
B: false
C: true
decltype(C::alpha): true