std::byteswap

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Function objects Bit manipulation (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23)

 

Bit manipulation

bit_cast (C++20)

byteswap (C++23)

Integral powers of 2

has_single_bit (C++20)

bit_ceil (C++20)

bit_floor (C++20)

bit_width (C++20)

Rotating

rotl (C++20)

rotr (C++20)

Counting

countl_zero (C++20)

countl_one (C++20)

countr_zero (C++20)

countr_one (C++20)

popcount (C++20)

Endian

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	Feature
__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)