[FYI] Forward movement on 9404

[Benjamin Kosnik]

>in case someone would like to help on testing/adding comments and
>what else, before taking a little bit of sleep I'm sending my current
>best attempt at fixing 9404 in a clean way, i.e., implementing the
>more general points of Nathan's outline for a post-DR169 asset.

Great job.

>I'm quite happy with it! Of course the regression tests are ok and
>everything seems quite clean: overflow now happens _always_ when it
>should (pptr == epptr) both for filestreams and stringstreams.

Absolutely fantastic.

>I would appreciate, in particular, some help on the legacy <strstream>
>bits, which must be broken right now.

I think <strstream> should be separate from this, and should not hold
this patch up.

A minor nit:

+	      if (_M_out_buf_size())
 		__ret = this->sputc(traits_type::to_char_type(__c));
 	      else if (__len <= _M_string.max_size())
 		{
 		  // Force-allocate, re-sync.
 		  _M_string = this->str();
 		  _M_string.reserve(__len);
-		  this->_M_buf_size = __len;
+		  this->_M_buf_size = _M_string.capacity();
 		  _M_really_sync(this->_M_in_cur - this->_M_in_beg, 
 				 this->_M_out_cur - this->_M_out_beg);
 		  __ret = this->sputc(traits_type::to_char_type(__c));

is there a way to coalesce these

__ret = this->sputc(traits_type::to_char_type(__c));

lines?

-benjamin