# std::byte

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< cpp‎ | types

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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