libstdc++/10094: Regression: wfilebuf::showmanyc return value too high.

[peturr02 at ru dot is]

>Number:         10094
>Category:       libstdc++
>Synopsis:       Regression: wfilebuf::showmanyc return value too high.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 15 10:46:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     peturr02 at ru dot is
>Release:        gcc mainline from 20030312
>Organization:
>Environment:
Red Hat Linux 8.0
>Description:
The return value of wfilebuf::showmanyc is only calculated from codecvt::max_length and the number of bytes in the file. This means that when the file contains illegal multibyte sequences, showmanyc promises more characters than underflow can deliver.
>How-To-Repeat:
See attachment.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="showmanycbug2.cc"
Content-Disposition: inline; filename="showmanycbug2.cc"

#include <fstream>
#include <locale>

#undef NDEBUG
#include <cassert>

int main()
{
	using namespace std;

	const char* name = "tmp";
	const char* strlit = "\xc0\xff For What You Dream Of";
	
	filebuf fbout;
	fbout.open(name, ios_base::out | ios_base::trunc);

	for (int i = 0; i < BUFSIZ; ++i)
		fbout.sputc('a');

	fbout.sputn(strlit, strlen(strlit));
	fbout.close();

	wfilebuf fbin;
	fbin.pubimbue(locale("se_NO.UTF-8"));
	fbin.open(name, ios_base::in);

	streamsize n = fbin.in_avail();
	while (n > 0)
	{
		if (--n == 0)
			n = fbin.in_avail();

		wfilebuf::int_type c = fbin.sbumpc();
		assert(c != wfilebuf::traits_type::eof());
	}

	fbin.close();

	return 0;
}