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Defined in header <utility> | ||
template<class Enum> constexprstd::underlying_type_t<Enum> to_underlying( Enum e)noexcept; | (since C++23) | |
Converts an enumeration to its underlying type. Equivalent toreturnstatic_cast<std::underlying_type_t<Enum>>(e);.
Contents |
| e | - | enumeration value to convert |
The integer value of the underlying type ofEnum, converted frome.
std::to_underlying can be used to avoid converting an enumeration to an integer type other than its underlying type.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_to_underlying | 202102L | (C++23) | std::to_underlying |
#include <cstdint>#include <iomanip>#include <iostream>#include <type_traits>#include <utility> enumclass E1:char{ e};static_assert(std::is_same_v<char, decltype(std::to_underlying(E1::e))>); enumstruct E2:long{ e};static_assert(std::is_same_v<long, decltype(std::to_underlying(E2::e))>); enum E3:unsigned{ e};static_assert(std::is_same_v<unsigned, decltype(std::to_underlying(e))>); int main(){enumclass ColorMask:std::uint32_t{ red=0xFF, green=(red<<8), blue=(green<<8), alpha=(blue<<8)}; std::cout<<std::hex<<std::uppercase<<std::setfill('0')<<std::setw(8)<< std::to_underlying(ColorMask::red)<<'\n'<<std::setw(8)<< std::to_underlying(ColorMask::green)<<'\n'<<std::setw(8)<< std::to_underlying(ColorMask::blue)<<'\n'<<std::setw(8)<< std::to_underlying(ColorMask::alpha)<<'\n'; // std::underlying_type_t<ColorMask> x = ColorMask::alpha; // Error: no known conversion[[maybe_unused]]std::underlying_type_t<ColorMask> y= std::to_underlying(ColorMask::alpha);// OK}
Output:
000000FF0000FF0000FF0000FF000000
(C++11) | obtains the underlying integer type for a given enumeration type (class template)[edit] |
(C++11) | checks if a type is an enumeration type (class template)[edit] |
(C++23) | checks if a type is a scoped enumeration type (class template)[edit] |
