endianness.cpp

#include <iostream>

enum class Endianness
{
    LITTLE,
    BIG
};

Endianness makeEndianness()
{              
    union U
    {
        uint8_t  u8;
        uint16_t u16 = 1;
    };
    
    return U{}.u8 ? Endianness::LITTLE
                  : Endianness::BIG;
}

static const auto ENDIANNESS = makeEndianness();

int main()
{
    if (ENDIANNESS == Endianness::LITTLE ) { std::cout << "LITTLE" << std::endl; }
    if (ENDIANNESS == Endianness::BIG    ) { std::cout << "BIG"    << std::endl; }
    
    return 0;    
}