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Subject: [Bug c/49182] Fordward declarations of struct not usable in function pointer types.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49182

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-26 23:44:43 UTC ---
(In reply to comment #3)
> (In reply to comment #2)
> > I forgot to mention GCC compiles it correctly with the C++ front-end.
> 
> Removing the typedefs will still cause compilation to error out not knowing
> what a is.  For example:
> 
> // Forward declaration
> struct a;  

You've declared the type "struct a"

> // Pointer to function with struct as parameter
> typedef int (*FxnPointer)(a* WontComplie);

You've tried to use "a" which is undeclared

> // Actual declaration of struct with function pointer type declared above.
> struct _a
> {
>     int foo;
>     int bar;
>     FxnPointer PtrToFxn;
> } a;

Now you've declared a variable called "a" with type "struct _a"