C++17中std::byte的具体使用详解

enum class byte : unsigned char {};

template< class T >
inline constexpr bool is_integral_v = is_integral<T>::value;

namespace {
 
std::ostream& operator<<(std::ostream& os, std::byte b)
{
    return os << std::bitset<8>(std::to_integer<int>(b));
}
 
} // namespace
 
int test_byte()
{
    // 注意：列表初始化(使用花括号初始化)是唯一可以直接初始化std::byte对象的方法
    std::byte b{ 66 };
    std::cout << b << "\n"; // 01000010
 
    std::byte b2 = b << 1;
    std::cout << b2 << "\n"; // 10000100
    b <<= 1;
    std::cout << b << "\n"; // 10000100
 
    std::byte b3 = b >> 1;
    std::cout << b3 << "\n"; // 01000010
    b >>= 1;
    std::cout << b << "\n"; // 01000010
 
    std::byte b4 = b | std::byte{ 0b11110000 };
    std::cout << b4 << "\n"; // 11110010
    b |= std::byte{ 0b11110000 };
    std::cout << b << "\n"; // 11110010
 
    b4 = b & std::byte{ 0b11110000 };
    std::cout << b4 << "\n"; // 11110000
    b &= std::byte{ 0b11110000 };
    std::cout << b << "\n"; // 11110000
 
    b4 = b ^ std::byte{ 0b11111111 };
    std::cout << b4 << "\n"; // 00001111
    b ^= std::byte{ 0b11111111 };
    std::cout << b << "\n"; // 00001111
 
    b4 = ~b;
    std::cout << b4 << "\n"; // 11110000
 
    std::byte b5;
    //std::cout << b5 << "\n"; // error: 如果没有初始化，std::byte对象的值是未定义的，因为它存储在栈上
 
    std::byte b6{};
    std::cout << b6 << "\n"; // 00000000
 
    std::cout << "sizeof std::byte: " << sizeof(std::byte) << "\n"; // sizeof std::byte: 1
 
    std::byte b7{ 0xFF };
    std::cout << std::to_integer<unsigned int>(b7) << ","
        << std::to_integer<int>(b7) << ","
        << static_cast<int>(std::to_integer<signed char>(b7)) << "\n"; // 255,255,-1
 
    return 0;
}