Re: [Boost-users] Re: Can't get "write" to work when using IOStreams withcustom streambuf

From: Eyal Susser (eyal.susser_at_[hidden])
Date: 2005-05-11 07:39:21

Thanks.

I'm using your code along with the serialization lib from boost. 
Together, they seem to be pretty powerful.  I used to think I was a
decent programmer, but you boost guys...what can I say.  Hats off.

On 5/8/05, Jonathan Turkanis <technews_at_[hidden]> wrote:
> Eyal Susser wrote:
> > Hi,
> >
> >    Boost is a really neat idea, I wish I had less trouble using it (so
> > embarrasing...).  Anyway, here's a streambuf class I wrote using
> > IOStream :
> 
> <snip example>
> 
> > But the ouput from cout is an empty string, although when debugging I
> > can see m_pBuffer being copied to.
> 
> Hi,
> 
> Thanks for using the Iostreams library.
> 
> There are a few problems with you code:
> 
> The first, which you couldn't be expected to know, is that write() now returns a
> streamsize value indicating how many characters were written.
> 
> Second, the character type of iostreams::source is char, not unsigned char. If
> you want to use unsigned char, you can do:
> 
>     class CrIPCStreamOutput {
>     public:
>         typedef unsigned char char_type;
>         typedef sink_tag io_category;
>         /* ... */
>     };
> 
> But be warned that standard libraries may not let you instantiate a
> streambuf_facade with this char_type.
> 
> Third, you should flush the stream_facade after writing to it, to make sure that
> buffered data has made its way to your sink.
> 
> Fourth, the implementation of write is unsafe, since you don't check for
> overflow. Writing too many characters will lead to stack corruption.
> 
> Finally, and most importantly, you declare the member variable m_pBuffer as a
> *reference* to a pointer. When you pass an instance of CrIPCStreamOutput to the
> streambuf_facade constructor, a copy is made, and you end up with a reference to
> a temporary pointer rather than the original pointer. Declaring m_pBuffer to
> have type char* fixes this.
> 
> One last point is that if you want to define a stream which writes to a
> preexisting buffer, you can use an array_sink, defined in the header
> <boost/iostreams/device/array.hpp>:
> 
>     iostreams::stream_facade<iostreams::array_sink> out(buf, len);
> 
> > Thanks.
> 
> Jonathan
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>