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std::byteswap

From cppreference.com
< cpp‎ | numeric
Defined in header <bit>
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.

Contents

[edit] Parameters

n - integer value

[edit] Return value

An integer value of type T whose object representation comprises the bytes of that of n in reversed order.

[edit] Notes

This function is useful for processing data of different endianness.

[edit] 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

[edit] See also

(C++20)
indicates the endianness of scalar types
(enum) [edit]
(C++20)
computes the result of bitwise left-rotation
(function template) [edit]
(C++20)
computes the result of bitwise right-rotation
(function template) [edit]