NAME¶

std::byte - std::byte

Synopsis¶

Defined in header <cstddef>
enum class byte : unsigned char {}; (since C++17)

std::byte is a distinct type that implements the concept of byte as specified in the
C++ language definition.

Like unsigned char, it can be used to access raw memory occupied by other objects
(object representation), but unlike unsigned char, it is not a character type and is
not an arithmetic type. std::byte models a mere collection of bits, supporting only
bitshift operations with an integer, and bitwise and comparison operations with
another std::byte.

Non-member functions¶

std::to_integer

template <class IntegerType> (since C++17)
constexpr IntegerType to_integer( std::byte b ) noexcept;

Equivalent to: return IntegerType(b); This overload participates in overload
resolution only if std::is_integral_v<IntegerType> is true.

std::operator<<=,operator>>=

template <class IntegerType>
constexpr std::byte& operator<<=( std::byte& b, IntegerType shift (1) (since C++17)
) noexcept;
template <class IntegerType>
constexpr std::byte& operator>>=( std::byte& b, IntegerType shift (2) (since C++17)
) noexcept;

1) Equivalent to: return b = b << shift; This overload participates in overload
resolution only if std::is_integral_v<IntegerType> is true.
2) Equivalent to: return b = b >> shift;

This overload participates in overload resolution only if
std::is_integral_v<IntegerType> is true.

std::operator<<,operator>>

template <class IntegerType>
constexpr std::byte operator<<( std::byte b, IntegerType shift ) (1) (since C++17)
noexcept;
template <class IntegerType>
constexpr std::byte operator>>( std::byte b, IntegerType shift ) (2) (since C++17)
noexcept;

1) Equivalent to: return std::byte(static_cast<unsigned int>(b) << shift); This
overload participates in overload resolution only if std::is_integral_v<IntegerType>
is true.
2) Equivalent to: return std::byte(static_cast<unsigned int>(b) >> shift);

This overload participates in overload resolution only if
std::is_integral_v<IntegerType> is true.

std::operator|=,operator&=,operator^=

constexpr std::byte& operator|=( std::byte& l, std::byte r ) (1) (since C++17)
noexcept;
constexpr std::byte& operator&=( std::byte& l, std::byte r ) (2) (since C++17)
noexcept;
constexpr std::byte& operator^=( std::byte& l, std::byte r ) (3) (since C++17)
noexcept;

1) Equivalent to: return l = l | r;.
2) Equivalent to: return l = l & r;.
3) Equivalent to: return l = l ^ r;.

std::operator|,operator&,operator^,operator~

constexpr std::byte operator|( std::byte l, std::byte r ) (1) (since C++17)
noexcept;
constexpr std::byte operator&( std::byte l, std::byte r ) (2) (since C++17)
noexcept;
constexpr std::byte operator^( std::byte l, std::byte r ) (3) (since C++17)
noexcept;
constexpr std::byte operator~( std::byte b ) noexcept; (4) (since C++17)

1) Equivalent to: return std::byte(static_cast<unsigned int>(l) |
static_cast<unsigned int>(r));.
2) Equivalent to: return std::byte(static_cast<unsigned int>(l) &
static_cast<unsigned int>(r));.
3) Equivalent to: return std::byte(static_cast<unsigned int>(l) ^
static_cast<unsigned int>(r));.
4) Equivalent to: return std::byte(~static_cast<unsigned int>(b));

Notes¶

A numeric value n can be converted to a byte value using std::byte{n}, due to C++17
relaxed enum class initialization rules.

A byte can be converted to a numeric value (such as to produce an integer hash of an
object) the usual way with an explicit conversion or alternatively with
std::to_integer.

Feature-test macro Value Std Feature
__cpp_lib_byte 201603L (C++17) std::byte

Example¶

// Run this code

#include <bitset>
#include <cstddef>
#include <iostream>
#include <utility>

std::ostream& operator<<(std::ostream& os, std::byte b)
{
return os << std::bitset<8>(std::to_integer<int>(b));
}

int main()
{
// std::byte y = 1; // Error: cannot convert int to byte.
std::byte y{1}; // OK

// if (y == 13) {} // Error: cannot be compared.
if (y == std::byte{13}) {} // OK, bytes are comparable

int arr[]{1, 2, 3};
// int c = a[y]; // Error: array subscript is not an integer
[[maybe_unused]] int i = arr[std::to_integer<int>(y)]; // OK
[[maybe_unused]] int j = arr[std::to_underlying(y)]; // OK

std::byte b{42};
std::cout << "1. " << b << '\n';

// b *= 2; // Error: b is not of arithmetic type
b <<= 1;
std::cout << "2. " << b << '\n';

b >>= 1;
std::cout << "3. " << b << '\n';

std::cout << "4. " << (b << 1) << '\n';
std::cout << "5. " << (b >> 1) << '\n';

b |= std::byte{0b11110000};
std::cout << "6. " << b << '\n';

b &= std::byte{0b11110000};
std::cout << "7. " << b << '\n';

b ^= std::byte{0b11111111};
std::cout << "8. " << b << '\n';
}

Output:¶

1. 00101010
2. 01010100
3. 00101010
4. 01010100
5. 00010101
6. 11111010
7. 11110000
8. 00001111