Re: [v3] libstdc++/38678

[Martin Sebor <sebor at roguewave dot com>]

Paolo Carlini wrote:
> Hi,
> > FWIW, calling sbumpc() for each character is inefficient,
> > especially when the size of the internal buffer is much
> > less than the size of the buffer being stored into, such
> > as in the unbuffered case. I suggest calling
> > streambuf::xsgetn() directly instead, like so:
> >
> > +  template<typename _CharT, typename _Traits>
> >      basic_istream<_CharT, _Traits>&
> >      basic_istream<_CharT, _Traits>::
> >      read(char_type* __s, streamsize __n)
> > @@ -611,7 +627,7 @@
> >        ios_base::iostate __err = ios_base::iostate(ios_base::goodbit);
> >        try
> >          {
> > -          _M_gcount = this->rdbuf()->sgetn(__s, __n);
> > +             typedef basic_streambuf<_CharT, _Traits> _Streambuf;
> > +          _M_gcount = this->rdbuf()->_Streambuf::xsgetn(__s, __n);
> >            if (_M_gcount != __n)
> >          __err |= (ios_base::eofbit | ios_base::failbit);
> >          }
> >
> > (This requires that basic_streambuf be granted friendship
> > of basic_istream.)
> Of course, and because of that I adopted the general strategy used
> already in many other places: when we can rely on friendship, we have
> control on it (that is, basic_streambuf<char> and
> basic_streambuf<wchar_t>, that is instantiations the user cannot provide
> replacement specializations for) I added a fast specialization relying
> on xsgetn / xsputn, otherwise, we have the slow generic version, using
> only the public members of the streambuf.\

Ah, I had missed that in the patch.

Btw., the spec already allows ostream to call xsputn(), so
there should be no need to avoid calling it as the patch does.

Martin


> Paolo.