How to query target architecture endianness during gcc compilation?

Question

I would like to promote more of my endianness logic to compile time constexpr's. I know that in C++20, this is highly standardized via std::endian. However, for the moment I am targeting C++17.

How can I query the target architecture's endianness from within my C++ code? Prefer simple constexpr functions and macros to autoconf. Would appreciate working snippets for GCC, Clang, and MSVC.

Have you read the documentation for the compilers you mention? Especially what preprocessor macros they might define for identifying the target system? — Some programmer dude, Oct 13 '21 at 15:57
Related to [c-macro-definition-to-determine-big-endian-or-little-endian-machine](https://stackoverflow.com/questions/2100331/c-macro-definition-to-determine-big-endian-or-little-endian-machine). — Jarod42, Oct 13 '21 at 16:04
https://stackoverflow.com/a/40675229/9072753 what research did you do? — KamilCuk, Oct 13 '21 at 17:09

score 0 · Answer 1 · answered Oct 13 '21 at 16:03

0

You can use preprocessor defined macros of GCC like below

#if __BYTE_ORDER == __BIG_ENDIAN

or

#if __BYTE_ORDER == __LITTLE_ENDIAN

You've to include #include <endian.h> header

answered Oct 13 '21 at 16:03

Harry

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score 0 · Answer 2 · answered Oct 14 '21 at 00:27

For a cross-platform solution you can use Boost.Predef which is a preprocessor header that even works with C. It contains various predefined macros for the target platform including the endianness (BOOST_ENDIAN_*)

#if BOOST_ENDIAN_BIG_BYTE
    std::cout << "Big endian!";
#elif BOOST_ENDIAN_LITTLE_BYTE
    std::cout << "Little endian!";
#endif

How to query target architecture endianness during gcc compilation?

2 Answers2