Where can I find a list of constants declared in Standard Library Headers

Question

I'm writing some serialization code, and obiously, this code needs to know if the result should be big or little endian, so I tried declaring an enum like this:

namespace TerrainGenerator
{
    ...
    enum Endianess {LITTLE_ENDIAN, BIG_ENDIAN};
    ...
}

But for some reason, my IntelliSense was telling me that these values are already declared.

Running g++ also gave me errors, telling me they had been defined as 1234 and 4321 (for little and big endian respectively).

I noticed the errors went away when I stopped including <string>.

Is there somewhere I can find a list of constants that have been declared in the std. libs?

I'm running Arch Linux, Kernel 4.12.8-2-ARCH.

Running strings /usr/lib/libstdc++.so.6 | grep LIBCXX returns a bunch of lines, the highest version number being GLIBCXX_3.4.24.

Running ldconfig -p | grep stdc++ returns:

libstdc++.so.6 (libc6,x86-64) => /usr/lib/libstdc++.so.6
libstdc++.so (libc6,x86-64) => /usr/lib/libstdc++.so

(as suggested by https://stackoverflow.com/a/10355215/6242052 to find what version of the std. libs i'm using)

EDIT: If these values are #defined, on a scale of 1-10 how bad of an idea would it be to #undef them after including all headers? (And possibly re-#define-ing them after my code)