std::byteswap
Defined in header <bit> |
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template< class T > constexpr T byteswap( T n ) noexcept; |
(since C++23) |
Reverses the bytes in the given integer value n.
std::byteswap participates in overload resolution only if T satisfies integral, i.e., T is an integer type. The program is ill-formed if T has padding bits.
Parameters
| n | - | integer value |
Return value
An integer value of type T whose object representation comprises the bytes of that of n in reversed order.
Notes
This function is useful for processing data of different endianness.
Feature testing macro: __cpp_lib_byteswap.
Possible implementation
template<std::integral T>
constexpr T byteswap(T value) noexcept
{
static_assert(std::has_unique_object_representations_v<T>, "T may not have padding bits");
auto value_representation = std::bit_cast<std::array<std::byte, sizeof(T)>>(value);
std::ranges::reverse(value_representation);
return std::bit_cast<T>(value_representation);
}
|
Example
#include <bit>
#include <cstdint>
#include <concepts>
#include <iostream>
#include <iomanip>
template <std::integral T>
void dump(T v, char term = '\n') {
std::cout << std::hex << std::uppercase << std::setfill('0')
<< std::setw(sizeof(T) * 2) << v << " : ";
for (std::size_t i{}; i != sizeof(T); ++i, v >>= 8) {
std::cout << std::setw(2) << static_cast<unsigned>(T(0xFF) & v) << ' ';
}
std::cout << std::dec << term;
}
int main()
{
static_assert(std::byteswap('a') == 'a');
std::cout << "byteswap for U16:\n";
constexpr auto x = std::uint16_t(0xCAFE);
dump(x);
dump(std::byteswap(x));
std::cout << "\nbyteswap for U32:\n";
constexpr auto y = std::uint32_t(0xDEADBEEFu);
dump(y);
dump(std::byteswap(y));
std::cout << "\nbyteswap for U64:\n";
constexpr auto z = std::uint64_t{0x0123456789ABCDEFull};
dump(z);
dump(std::byteswap(z));
}
Possible output:
byteswap for U16: CAFE : FE CA FECA : CA FE byteswap for U32: DEADBEEF : EF BE AD DE EFBEADDE : DE AD BE EF byteswap for U64: 0123456789ABCDEF : EF CD AB 89 67 45 23 01 EFCDAB8967452301 : 01 23 45 67 89 AB CD EF
See also
|
(C++20)
|
indicates the endianness of scalar types (enum) |
|
(C++20)
|
computes the result of bitwise left-rotation (function template) |
|
(C++20)
|
computes the result of bitwise right-rotation (function template) |
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https://en.cppreference.com/w/cpp/numeric/byteswap
