Re: [boost] Re: [iostreams(jonathan)] - using with 1.32

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-11-24 17:23:50

Jonathan Turkanis wrote:
> "Reece Dunn" <msclrhd_at_[hidden]> wrote in message
>>I am playing around with the library. Here are a few thoughts:
>>
>>[1] And is it possible to access Sink members from stream_facade, for
>>example:
>>
> This would require stream_facade to derive from the policy class, which I didn't
> do for several reasons. The way to access the policy is with operators * or ->:
>
>   stream_facade< speech_reader > speech;
>   speech->set_pitch( 50 );
>   // Or: (*speech).set_pitch( 50 );

That is still just as good :).

>>[2] I would like to collapse:
>>
>>    std::ofstream out( "encoded.txt" );
>>    boost::io::filtering_ostream os;
>>    os.push( ascii85_encoder());
>>    os.push( out );
>>    os << ...;
>>
>>to:
>>
>>    class ascii85_ofstream: public boost::io::filtering_ostream
>>    {
>>       std::ofstream out;
>>       public:
>>          ascii85_ofstream( const char * fn ): out( fn )
>>          {
>>             push( ascii85_encoder());
>>             push( out );
>>          }
>>    };
>>
>>    ascii85_ofstream os( "encoded.txt" );
>>    os << ...;
>
> Yes, this is certainly one of the intended uses of the library.
>
>>but this results in a crash at the destructor (tested with msvc-8.0).
>>
> I believe the problem is that the filtering_ostream (a base class) is accessing
> the ofstream (a member of a derived class) after the ofstream has been
> destroyed.

This was my thoughts as well.

> This would be unacceptable even if filtering_ostream had a
> no-close-on-exit option. I believe the solution is to pop the ofstream in the
> ascii85_ofstream destructor.
>
>      ascii85_ofstream::~ascii85_ofstream()
>      {
>         pop(); // Or: reset();
>      }
>
> Please let me know if this works.

pop() does indeed fix the problem :).

Regards,
Reece