Re: [Boost-users] Re: Re: Guidelines for effective exception usage

From: Stephen torri (storri_at_[hidden])
Date: 2004-08-23 14:48:47

On Mon, 2004-08-23 at 15:04, Jonathan Turkanis wrote:
> > 1)  Use virutal inheritance. I see the example and can understand
> why
> > its wrong I just do not understand how to fix it.
> 
> I believe in the example the fix is to use virtual inheritance in the
> definitions of  my_exc1 and my_exc2, so that later someone can derive
> from both. Using virtual inheritance in the definition of  your_exc3
> doen't help. I see that this advice is not followed consistently
> within boost (Robert Ramey's serialization library is the only case I
> can find). But it's still good advice, I think.

To do virtual inheritance I was under the belief that the base class had
only pure virtual methods. Each subclass then implements the virtual
methods. Is this what was intended or am I misunderstanding the term
virtual inheritance?

> Often you can get away with:
> 
> class Data_Exception : public std::exception {
> public:
>      Data_Exception(int code) : code_(code) { }
>      virtual const char* what() const throw()
>      {
>           [return result of looking up code in a table of error
> messages.]
>      }
> private:
>      int code;
> };
> 

So each class has a predefined table of int/string pairs. This table
should be a static member of this class because there is not need to
have multiple instances.

Can you use a std::map or sgi hash_map to construct the table?

Stephen
-- 
Email: storri_at_[hidden]