std::to_underlying
cppreference.com
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template< class Enum > constexpr std::underlying_type_t<Enum> to_underlying( Enum e ) noexcept; |
( C++23) | |
. return static_cast<std::underlying_type_t<Enum>>(e);.
| e |
Enum, e.
std::to_underlying , , .
__cpp_lib_to_underlying |
202102L |
(C++23) | std::to_underlying
|
#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_underlying(E1::e))>);
enum struct 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()
{
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;
[[maybe_unused]]
std::underlying_type_t<ColorMask> y = std::to_underlying(ColorMask::alpha); // OK
}
:
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