g++ compiling C++11 using -Wpedantic option: Is there an option to disable only the warning about unnamed structs?

Question

I want to keep any other checks -Wpedantic does but lose the warning about unnamed structs error: ISO C++ prohibits anonymous structs [-Wpedantic].

I want to be able to do the following:

union
{
  struct
  {
    float x, y, z, w;
  };
  struct
  {
    float r, g, b, a;
  };

  float v[4];
};

---

What I've found so far

I'm using C++11 and compiling with the -std=c++11 flag. I've read that C11 supports this feature, but I haven't seen any mention of it being supported in C++11.

I've come across mention of -fms-extensions:

• In this SO question about C for which it is the accepted answer

• In the GCC documentation for the flag's use when compiling C++ which doesn't give very many details

I tried the flag and it doesn't appear to have any effect (no matter the permutation of ordering between -fms-extensions and -Wpedantic).

EDIT - More details

Thanks to the comments I've found the following:

• Details about why unnamed classes/structs are not fully conformant with the standard

• A post that claims my example code relies on undefined behavior

I'd still like to know if there is a method of enabling this gcc extension (which all compilers I know of have) that will disable the warning. Or is -Wpedantic all or nothing?

Answer 1

You can disable -Wpedantic temporarily, for example if you have old code in some include file:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"
#include "old_header.hpp"
#pragma GCC diagnostic pop

Of course you could also do this on every occasion where you are using an anonymous struct to limit the scope where pedantic is disabled, but when you are doing that you could as well just go ahead and fix the code itself :)