libstdc++/10096: Input impossible with basic_filebuf with custom traits type.

[peturr02@ru.is]

>Number:         10096
>Category:       libstdc++
>Synopsis:       Input impossible with basic_filebuf with custom traits type.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 15 10:56:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     peturr02@ru.is
>Release:        gcc mainline from 20030312
>Organization:
>Environment:
Red Hat Linux 8.0
>Description:
basic_filebuf<CharT, Traits>::sbumpc() returns an endless stream of zeros when Traits is a user-defined traits class. This happens both when the file is closed and when it is open.
>How-To-Repeat:
See attachment.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="instbug2.cc"
Content-Disposition: inline; filename="instbug2.cc"

#include <fstream>
#include <cstring>

#undef NDEBUG
#include <cassert>

class MyTraits : public std::char_traits<char>
{
};

int main()
{
	using namespace std;

	const char* name = "tmp";
	const char* strlit = "The Grand Wazoo";
	streamsize len = strlen(strlit);

	filebuf fbout;
	fbout.open(name, ios_base::out | ios_base::trunc);
	fbout.sputn(strlit, len);
	fbout.close();

	char buf[1024];

	basic_filebuf<char, MyTraits> fb;
	assert(fb.sgetc() == MyTraits::eof());

	fb.open("instbug2.cc", ios_base::in);
	assert(fb.is_open());
	assert(fb.sgetc() != MyTraits::eof());

	streamsize n = fb.sgetn(buf, sizeof(buf));
	assert(n == len);
	assert(!memcmp(buf, strlit, len));

	fb.close();
	assert(!fb.is_open());
	assert(fb.sgetc() == MyTraits::eof());

	return 0;
}