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

From: Rupert Bruce (rupert_at_[hidden])
Date: 2008-06-02 10:41:37

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Michael Bradley Jr wrote:
> Hi,
> 
> i'm facing this problem may be someone on the list do have an elegant solution
> 
This is really not a boost-related problem; this is basic C++.
> 
> class A;
> class B;
> 
> class C {
> int operator () (A*,B*)
> };
Try making class C look more like this:

class C
    {
    int operator()();

    A aInstance;
    B bInstance;
    };
You can then modify the operator() function to use aInstance and
bInstance instead of using parameters to pass them in.
> 
> typedef int (*foobar)(A*,B*);
> void do_something(foobar cb);
Just a suggestion - eliminate all typedef statements from your code
until you really understand what your code is doing. Typedefs are merely
aliases that will add to your confusion.

> 
> C obj;
> do_something(obj);	*ERROR*
Yes, this is an error:
   - 'obj' is an instance of C that knows absolutely nothing about A or B
   - 'do_something()' is a function that expects a function pointer
(with pointer-to-A and pointer-to-B as its parameters) and knows nothing
about C

> 
> 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.
There is no class B member function mentioned anywhere in your sample...

> Any clue how to get rid of this?
> 
> Thanks in advance
> Mike
> 
> 
> 
> 
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 
> 

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