re PR libstdc++/12868 (basic_filebuf::imbue fails too easily)

re PR libstdc++/12868 (basic_filebuf::imbue fails too easily)

2003-11-18  Paolo Carlini  <pcarlini@suse.de>

	PR libstdc++/12868
	* include/bits/fstream.tcc (imbue): For encodings != -1 it's
	always ok to imbue a new locale, provided seekoff(0, cur, ...)
	doesn't fail, of course.
	(underflow): In order for the above to work, deal gracefully
	with _M_codecvt->in returning codecvt_base::error while
	(__ilen = __iend - this->eback()) > 0: it just means __ilen
	correctly converted internal characters before an error.
	* testsuite/27_io/basic_filebuf/imbue/wchar_t/12868.cc: New.

From-SVN: r73697