std::byte

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

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

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

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

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 ) noexcept;	(1)	(since C++17)
constexpr std::byte operator&( std::byte l, std::byte r ) noexcept;	(2)	(since C++17)
constexpr std::byte operator^( std::byte l, std::byte r ) noexcept;	(3)	(since C++17)
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 <cassert>
#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
 
    auto to_int = [](std::byte b) { return std::to_integer<int>(b); };
 
    std::byte b{42};
    assert(to_int(b) == 0b00101010);
    std::cout << b << '\n';
 
    // b *= 2; // Error: b is not of arithmetic type
    b <<= 1;
    assert(to_int(b) == 0b01010100);
 
    b >>= 1;
    assert(to_int(b) == 0b00101010);
 
    assert(to_int(b << 1) == 0b01010100);
    assert(to_int(b >> 1) == 0b00010101);
 
    b |= std::byte{0b11110000};
    assert(to_int(b) == 0b11111010);
 
    b &= std::byte{0b11110000};
    assert(to_int(b) == 0b11110000);
 
    b ^= std::byte{0b11111111};
    assert(to_int(b) == 0b00001111);
}

Output:

00101010

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