[RFC] libstdc++/9404 or weird stringbuf internals

[Benjamin Kosnik]

>Upon the first one, overflow is called since there isn't an
>allocated string. Therefore overflow allocates one, then calls
>sputc again, as prescribed by the standard (well, not really, in
>fact it does *this->_M_out_cur = traits_type::to_char_type(__c);
>which is not the same thing, but this is a minor nit which
>could be easily fixed with some performance implications...).

This should be fixed, and is an error in the current implementation.

You can test this with a derived streambuf with a sputc member. I didn't
do that, but it should probably be done.

As for the rest, it is an error with _M_out_end being set incorrectly.
Petur's right, if epptr() == pptr(), overflow, but that should not be
the case for the seconf sputc.

 // there is no condition in the standard that requires this.  
 // in fact, this should not be true.  
 assert(dsbuf.pub_epptr() == dsbuf.pub_pptr()); 

 // the standard says nothing about a mandated call to overflow here.
 called = false;
 dsbuf.sputc('a');
 assert(called);	// 20030212 fail

Don't know if this is that helpful.

-benjamin