Re: [Boost-users] boost & c-style calback issue

From: Nikolai N Fetissov (nikolai-boost_at_[hidden])
Date: 2008-06-02 10:17:53

> Hi,
>
> i'm facing this problem may be someone on the list do have an elegant
> solution
>
>
> class A;
> class B;
>
> class C {
> int operator () (A*,B*)
> };
>
> typedef int (*foobar)(A*,B*);
> void do_something(foobar cb);
>
> C obj;
> do_something(obj);	*ERROR*

Object of type C is not convertible to function
pointer type foobar.

>
> did try boost::function<int(A*,B*)> ftor = obj;
> do_something(ftor);	*ERROR*
>
> compiler generates in both cases the following error messages
> cannot convert parameter 2 from 'boost::function<Signature>' to 'int
> (__cdecl
> *)(A *,B *)'
>
>   with
> 1>        [
> 1>            Signature=int (A *, B *)
> 1>        ]
> 1>        No user-defined-conversion operator available that can perform
> this
> conversion, or the operator cannot be called
>
>
> I can't make the corresponding class B member function static due to
> side-effects.
> Any clue how to get rid of this?

You got it backwards - raw function pointer is convertible
to boost::function, not the other way around (compiler is
trying to tell you exactly that.)
Make 'do_something' take boost::function instead.

Hope this helps.
--
 Nikolai