std::underlying_type - cppreference.com (original) (raw)

| | | | | --------------------------------------------- | | ------------- | | template< class T > struct underlying_type; | | (since C++11) |

If T is a complete enumeration (enum) type, provides a member typedef type that names the underlying type of T.

If the program adds specializations for std::underlying_type, the behavior is undefined.

[edit] Member types

[edit] Helper types

| template< class T > using underlying_type_t = typename underlying_type<T>::type; | | (since C++14) | | -------------------------------------------------------------------------------------- | | ------------- |

[edit] Notes

Each enumeration type has an underlying type, which can be

1. Specified explicitly (both scoped and unscoped enumerations);
2. Omitted, in which case it is int for scoped enumerations or an implementation-defined integral type capable of representing all values of the enum (for unscoped enumerations).

[edit] Example

#include #include   enum e1 {}; enum class e2 {}; enum class e3 : unsigned {}; enum class e4 : int {};   int main() { constexpr bool e1_t = std::is_same_v<std::underlying_type_t, int>; constexpr bool e2_t = std::is_same_v<std::underlying_type_t, int>; constexpr bool e3_t = std::is_same_v<std::underlying_type_t, int>; constexpr bool e4_t = std::is_same_v<std::underlying_type_t, int>;   std::cout << "underlying type for 'e1' is " << (e1_t ? "int" : "non-int") << '\n' << "underlying type for 'e2' is " << (e2_t ? "int" : "non-int") << '\n' << "underlying type for 'e3' is " << (e3_t ? "int" : "non-int") << '\n' << "underlying type for 'e4' is " << (e4_t ? "int" : "non-int") << '\n'; }

Possible output:

underlying type for 'e1' is non-int underlying type for 'e2' is int underlying type for 'e3' is non-int underlying type for 'e4' is int

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | checks if a type is an enumeration type (class template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | | checks if a type is a scoped enumeration type (class template) [edit] | | | converts an enumeration to its underlying type (function template) [edit] |