std::byte(3)

🌸 NAME 🌸

std::byte - std::byte

okay bestie, this is std::byte(3) from the C++ Standard Libary manual — yes, that’s the manual name exactly, we’re not touching it 💅. This page is all about the byte type that is not out here acting like a number, and it’s lowkey iconic for raw-memory vibes. ✨

---

✨ Synopsis ✨

First, the shape of it:

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. Periodt.

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. No cap, it’s literally just bits doing bit things. 🦋

---

🫶 Non-member functions 🫶

Here’s the friend group of free functions. They’re all (since C++17), bestie.

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;
template <class IntegerType>
constexpr std::byte& operator>>=( std::byte& b, IntegerType shift ) noexcept;

(1) and (2) are both (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;
template <class IntegerType>
constexpr std::byte operator>>( std::byte b, IntegerType shift ) noexcept;

(1) and (2) are both (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;
constexpr std::byte& operator&=( std::byte& l, std::byte r ) noexcept;
constexpr std::byte& operator^=( std::byte& l, std::byte r ) noexcept;

(1), (2), and (3) are all (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;
constexpr std::byte operator&( std::byte l, std::byte r ) noexcept;
constexpr std::byte operator^( std::byte l, std::byte r ) noexcept;
constexpr std::byte operator~( std::byte b ) noexcept;

(1), (2), (3), and (4) are all (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. Cute, right? 🎀

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. Obsessed with the flexibility, honestly.

Feature-test macro vibes:

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

---

mwah 💋 that’s the whole page, bestie — source is http://cppreference.com, date stamp is 2024.06.10, and the page is std::byte(3). Go forth and flex those bits responsibly. 💜