Using __attribute__ with typedef

Question

Apologies if the question seems too obvious or simple. Unfortunately, after going through a bunch of threads and googling about typedef coupled with attribute prefix, I am still not able to it figure out.

I have a following snippet of code in a (supposedly) portable app -

#ifdef WIN32
#define MY_PREFIX __declspec(dllexport)
#else
#define MY_PREFIX __attribute__((visibility("default")))
#endif

typedef MY_PREFIX bool some_func(void);

So my question is this -
1) What is that typedef exactly doing?
2) The code compiles fine on VS2008, but on G++ (gcc-4.1), I get a warning "‘visibility’ attribute ignored"
Is there any way I can remove that warning? (Omitting -Wattributes is not an option)

Thanks!

Answer 1

AFAIK in GCC visibility attribute for function type cannot be "wrapped" into a typedef-ed type. The compiler assumes that this visibility attribute applies to the typedef-name itself. And GCC does not support visibility for typedef names (and it is not what you need anyway).

I'd say that instead of trying to wrap the declspec/attribute into the typedef, it should be specified explicitly at the point of function declaration. As in

#ifdef WIN32
#define MY_PREFIX __declspec(dllexport)
#else
#define MY_PREFIX __attribute__((visibility("default")))
#endif

typedef bool some_func(void);

MY_PREFIX some_func foo; // <- actual declaration

This will, of course, make is less clean, since instead of specifying MY_PREFIX once inside the typedef it should now be specified in every function declaration. But that's probably the only way to make it work, unless I'm missing something.