std::to_underlying
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Defined in header
<utility>
template< class Enum >
constexpr std::underlying_type_t <Enum> to_underlying( Enum e ) noexcept;
(since C++23)
constexpr std::underlying_type_t <Enum> to_underlying( Enum e ) noexcept;
Converts an enumeration to its underlying type. Equivalent to return static_cast<std::underlying_type_t <Enum>>(e);.
Contents
[edit] Parameters
e
-
enumeration value to convert
[edit] Return value
The integer value of the underlying type of Enum, converted from e.
[edit] 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
|
[edit] 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_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; // Error: no known conversion [[maybe_unused]] std::underlying_type_t <ColorMask> y = std::to_underlying(ColorMask::alpha); // OK }
Output:
000000FF 0000FF00 00FF0000 FF000000