Re: [boost] Official boost macro to determine endianess?

Subject: Re: [boost] Official boost macro to determine endianess?
From: Frédéric Bron (frederic.bron_at_[hidden])
Date: 2017-04-05 12:29:37

Sorry, I should not have used #elif, in fact ALL macros are defined!
BOOST_ENDIAN_BIG_BYTE
BOOST_ENDIAN_BIG_WORD
BOOST_ENDIAN_LITTLE_BYTE
BOOST_ENDIAN_LITTLE_WORD
What does this mean?

I see that g++ has
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__

Frédéric

2017-04-05 14:23 GMT+02:00 Frédéric Bron <frederic.bron_at_[hidden]>:
>> I think the modern way to do this is to use Boost.Predef[1].
>
> I used predef in a small program (see below) but I'm surprised by the output:
> BOOST_ENDIAN_BIG_BYTE
> value= 0102
> memory=0201
>
> predef says I am big endian but I see that most significant byte
> (0x01) is stored at the end which seems to indicate little endian.
> My processor is: Intel(R) Core(TM) i7-6700HQ
>
> Frédéric
>
> Program:
> #include <cstdint>
> #include <iomanip>
> #include <iostream>
>
> #include <boost/predef.h>
>
> int main() {
> #if defined(BOOST_ENDIAN_BIG_BYTE)
>   std::cerr << "BOOST_ENDIAN_BIG_BYTE\n";
> #elif defined(BOOST_ENDIAN_BIG_WORD)
>   std::cerr << "BOOST_ENDIAN_BIG_WORD\n";
> #elif defined(BOOST_ENDIAN_LITTLE_BYTE)
>   std::cerr << "BOOST_ENDIAN_LITTLE_BYTE\n";
> #elif defined(BOOST_ENDIAN_LITTLE_WORD)
>   std::cerr << "BOOST_ENDIAN_LITTLE_WORD\n";
> #endif
>
>   std::cout << std::hex << std::setfill('0');
>
>   std::uint16_t value = 0x0102;
>   std::cout<<"value= "<<std::setw(4)<<value<<'\n';
>
>   auto c = reinterpret_cast<const std::uint8_t *>(&value);
>   std::cout<<"memory=";
>   for (int i = 0; i < (int)sizeof(value); ++i) {
>     std::cout << std::setw(2) << static_cast<int>(c[i]);
>   }
>   std::cout << '\n';
>
>   return 0;
> }