std::byteswap

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Numerics library

Common mathematical functions

Mathematical special functions (C++17)

Mathematical constants (C++20)

Floating-point environment (C++11)

Complex numbers

Numeric arrays

Pseudo-random number generation

Factor operations

gcd (C++17)

lcm (C++17)

Interpolations

midpoint (C++20)

lerp (C++20)

Generic numeric operations

iota (C++11)

ranges::iota (C++23)

accumulate

inner_product

adjacent_difference

partial_sum

reduce (C++17)

transform_reduce (C++17)

inclusive_scan (C++17)

exclusive_scan (C++17)

transform_inclusive_scan (C++17)

transform_exclusive_scan (C++17)

Bit operations

bit_cast (C++20)

byteswap (C++23)

has_single_bit (C++20)

bit_ceil (C++20)

bit_floor (C++20)

bit_width (C++20)

rotl (C++20)

rotr (C++20)

countl_zero (C++20)

countl_one (C++20)

countr_zero (C++20)

countr_one (C++20)

popcount (C++20)

endian (C++20)

 

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.

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-test macro	Value	Std	Comment
__cpp_lib_byteswap	202110L	(C++23)	std::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

Run this code

#include <bit>
#include <concepts>
#include <cstdint>
#include <iomanip>
#include <iostream>
 
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

endian (C++20)	indicates the endianness of scalar types (enum)
rotl (C++20)	computes the result of bitwise left-rotation (function template)
rotr (C++20)	computes the result of bitwise right-rotation (function template)