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std::to_underlying(3) C++ Standard Libary std::to_underlying(3) NAME std::to_underlying - std::to_underlying Synopsis Defined in header <utility> template< class Enum > constexpr std::underlying_type_t<Enum> to_underlying( Enum e ) (since C++23) noexcept; Converts an enumeration to its underlying type. Equivalent to return static_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. Feature-test macro Value Std Feature __cpp_lib_to_underlying 202102L (C++23) std::to_underlying Example // Run this code #include <cstdint> #include <iomanip> #include <iostream> #include <type_traits> #include <utility> enum class E1 : char { e }; static_assert(std::is_same_v<char, decltype(std::to_underly- ing(E1::e))>); enum struct E2 : long { e }; static_assert(std::is_same_v<long, decltype(std::to_underly- ing(E2::e))>); enum E3 : unsigned { e }; static_assert(std::is_same_v<unsigned, decltype(std::to_underly- ing(e))>); int main() { enum class 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(Color- Mask::alpha); // OK } Output: 000000FF 0000FF00 00FF0000 FF000000 See also underlying_type obtains the underlying integer type for a given enu- meration type (C++11) (class template) is_enum checks if a type is an enumeration type (C++11) (class template) is_scoped_enum checks if a type is a scoped enumeration type (C++23) (class template) http://cppreference.com 2024.06.10 std::to_underlying(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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