From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id F14AA384AB47; Thu, 2 May 2024 14:16:22 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org F14AA384AB47 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1714659382; bh=aFzOn8P4HATpfrXr6sKl6KmT9DnUcxT5KL2tMNkoyLY=; h=From:To:Subject:Date:In-Reply-To:References:From; b=RcCIvhTHqtm0Z+mj82/Eg84HBE5Pa9jxvO+Nj7bpCfu8JLYjVAx4GUitxVi3oNCWk t04Hx4DUjNLi8udCPbsdhqa9tmRch8vCm064IO7EGnbzZm51Ssr2pSgMY77BR0Bxk0 eu/LAlEja6Kk75coZr7fOWjr5ujazNAIT6bGvkHs= From: "cvs-commit at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/93672] [11/12/13 Regression] std::basic_istream::ignore hangs if delim MSB is set Date: Thu, 02 May 2024 14:16:20 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Version: 9.1.0 X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: cvs-commit at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: redi at gcc dot gnu.org X-Bugzilla-Target-Milestone: 11.5 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 List-Id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93672 --- Comment #7 from GCC Commits --- The releases/gcc-13 branch has been updated by Jonathan Wakely : https://gcc.gnu.org/g:fcf60d0baafa1245f768ac375dc60a07e92e9673 commit r13-8675-gfcf60d0baafa1245f768ac375dc60a07e92e9673 Author: Jonathan Wakely Date: Thu Apr 4 10:33:33 2024 +0100 libstdc++: Fix infinite loop in std::istream::ignore(n, delim) [PR93672] A negative delim value passed to std::istream::ignore can never match any character in the stream, because the comparison is done using traits_type::eq_int_type(sb->sgetc(), delim) and sgetc() never returns negative values (except at EOF). The optimized version of ignore for the std::istream specialization uses traits_type::find to locate the delim character in the streambuf, which _can_ match a negative delim on platforms where char is signed, but then we do another comparison using eq_int_type which fails. The code then keeps looping forever, with traits_type::find locating the character and traits_type::eq_int_type saying it's not a match, so traits_type::find is used again and finds the same character again. A possible fix would be to check with eq_int_type after a successful find, to see whether we really have a match. However, that would be suboptimal since we know that a negative delimiter will never match using eq_int_type. So a better fix is to adjust the check at the top of the function that handles delim=3D=3Deof(), so that we treat all negati= ve delim values as equivalent to EOF. That way we don't bother using find to search for something that will never match with eq_int_type. The version of ignore in the primary template doesn't need a change, because it doesn't use traits_type::find, instead characters are extracted one-by-one and always matched using eq_int_type. That avoids the inconsistency between find and eq_int_type. The specialization for std::wistream does use traits_type::find, but traits_type::to_int_type is equivalent to an implicit conversion from wchar_t to wint_t, so passing a wchar_t directly to ignore without using to_int_type works. libstdc++-v3/ChangeLog: PR libstdc++/93672 * src/c++98/istream.cc (istream::ignore(streamsize, int_type)): Treat all negative delimiter values as eof(). * testsuite/27_io/basic_istream/ignore/char/93672.cc: New test. * testsuite/27_io/basic_istream/ignore/wchar_t/93672.cc: New test. (cherry picked from commit 2d694414ada8e3b58f504c1b175d31088529632e)=