Is there a way to do a C++ style compile-time assertion to determine machine's endianness?

Question

I have some low level serialization code that is templated, and I need to know the system's endianness at compiletime obviously (because the templates specializes based on the system's endianness).

Right now I have a header with some platform defines, but I'd rather have someway to make assertions about endianness with some templated test (like a static_assert or boost_if). Reason being my code will need to be compiled and ran on a wide range of machines, of many specialized vendor, and probably devices that don't exist in 2008, so I can't really guess what might need to go into that header years down the road. And since the code-base has an expected lifetime of about 10 years. So I can't follow the code for-ever.

Hopefully this makes my situation clear.

So does anyone know of a compile-time test that can determine endianness, without relying on vendor specific defines?

Answer 1

If you're using autoconf, you can use the AC_C_BIGENDIAN macro, which is fairly guaranteed to work (setting the WORDS_BIGENDIAN define by default)

alternately, you could try something like the following (taken from autoconf) to get a test that will probably be optimized away (GCC, at least, removes the other branch)

int is_big_endian() {     union {         long int l;         char c[sizeof (long int)];     } u;      u.l = 1;      if (u.c[sizeof(long int)-1] == 1)     {         return 1;     }     else         return 0; } 

Answer 2

There is no portable way to do this at compile time, your best bet is probably to use the Boost endian macros or emulate the methods they use.