Converts an enumeration to its underlying type. Equivalent to return static_cast<std::underlying_type_t<Enum>>(e);.
[edit] Parameters e - enumeration value to convert [edit] Return valueThe 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.
#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[edit] See also obtains the underlying integer type for a given enumeration type
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