GCC ignores function attributes

[Nikos Chantziaras <realnc@xxxxxxxxx>]

According to the documentation:

https://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/Function-Attributes.html#Function-Attributes

and more specific, the example about the visibility attribute:

  void __attribute__ ((visibility ("protected")))
  f () { /* Do something. */; }

doesn't work for me. I have this C++ function prototype:

  const SDL_AudioSpec& __attribute__((visibility("default")))
  spec();

Compiling this with g++ 4.8.2 gives me:

  warning: 'visibility' attribute ignored on non-class types

I do not understand :-/  I found this bug on GCC's bugzilla:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30361

but it is very old and unconfirmed.

In any event, I have no idea what I am doing wrong here.