From cppreference.com
template<classEnum>constexprstd::underlying_type_t<Enum>to_underlying(Enume)noexcept;(since C++23)Converts an enumeration to its underlying type. Equivalent to returnstatic_cast<std::underlying_type_t<Enum>>(e);.
Parameters
e - enumeration value to convert Return value
The integer value of the underlying type of Enum, converted from e.
Notes
std::to_underlying can be used to avoid converting an enumeration to an integer type other than its underlying type.
macroValueStdFeature
(C++23)std::to_underlyingExample
Run this code
#include<cstdint>#include<iomanip>#include<iostream>#include<type_traits>#include<utility>enumclassE1:char{e};static_assert(std::is_same_v<char,decltype(std::to_underlying(E1::e))>);enumstructE2:long{e};static_assert(std::is_same_v<long,decltype(std::to_underlying(E2::e))>);enumE3:unsigned{e};static_assert(std::is_same_v<unsigned,decltype(std::to_underlying(e))>);intmain(){enumclassColorMask: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:
000000FF 0000FF00 00FF0000 FF000000 See also
(C++11)
obtains the underlying integer type for a given enumeration type
(class template)
(C++11)
checks if a type is an enumeration type
(class template)
(C++23)
checks if a type is a scoped enumeration type
(class template)