Defined in header <bit> | ||
---|---|---|
template< class To, class From > constexpr To bit_cast(const From& from) noexcept; | (since C++20) |
Obtain a value of type To
by reinterpreting the object representation of from
. Every bit in the value representation of the returned To
object is equal to the corresponding bit in the object representation of from
. The values of padding bits in the returned To
object are unspecified.
If there is no value of type To
corresponding to the value representation produced, the behavior is undefined. If there are multiple such values, which value is produced is unspecified.
This overload only participates in overload resolution if sizeof(To) == sizeof(From)
and both To
and From
are TriviallyCopyable types.
This function template is constexpr
if and only if each of To
, From
and the types of all subobjects of To
and From
:
An object of type To
whose value representation is as described above.
reinterpret_cast
(or equivalent explicit cast) between pointer or reference types shall not be used to reinterpret object representation in most cases because of the type aliasing rule.
Before std::bit_cast
, std::memcpy
can be used when it is needed to interpret the object representation as one of another type:
template <class To, class From> typename std::enable_if< (sizeof(To) == sizeof(From)) && std::is_trivially_copyable<From>::value && std::is_trivial<To>::value, // this implementation requires that To is trivially default constructible To>::type // constexpr support needs compiler magic bit_cast(const From &src) noexcept { To dst; std::memcpy(&dst, &src, sizeof(To)); return dst; }
#include <cstdint> #include <bit> #include <iostream> constexpr double f64v = 19880124.0; constexpr auto u64v = std::bit_cast<std::uint64_t>(f64v); constexpr std::uint64_t u64v2 = 0x3fe9000000000000ull; constexpr auto f64v2 = std::bit_cast<double>(u64v2); int main() { std::cout << std::fixed <<f64v << "f64.to_bits() == 0x" << std::hex << u64v << "u64\n"; std::cout << "f64::from_bits(0x" << std::hex << u64v2 << "u64) == " << std::fixed << f64v2 << "f64\n"; }
Possible output:
19880124.000000f64.to_bits() == 0x4172f58bc0000000u64 f64::from_bits(0x3fe9000000000000u64) == 0.781250f64
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