Defined in header <utility> | ||
|---|---|---|
template< class Enum > constexpr std::underlying_type_t<Enum> to_underlying( Enum e ) noexcept; | (since C++23) |
Converts an enumeration to its underlying type. Equivalent to return static_cast<std::underlying_type_t<Enum>>(e);.
| e | - | enumeration value to convert |
The integer value of the underlying type of Enum, converted from e.
std::to_underlying can be used to avoid converting an enumeration to an integer type other than its underlying type.
| Feature-test macro |
|---|
__cpp_lib_to_underlying |
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <type_traits>
#include <utility>
int main()
{
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))>);
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
|
(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) |
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