From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 455833858C39; Thu, 24 Aug 2023 11:37:52 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 455833858C39
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1692877072;
	bh=OgdbfhL20EestEtwwFvrQrmuWeklODxC9FTmkCKjwM8=;
	h=From:To:Subject:Date:From;
	b=ioR5WnXNGorVT61QbnbuE72XRetVNKfkIIRIn4Erko51Molo4uc+MwNlxhuyuHZiV
	 kkjsnXHvzVeojDa7ug0vVC0pMg22y+/aOneYGamG3TeKeOnoxHqI20fv5mAYJAxPAJ
	 qFtHd6byRM2CI38ySJJGbYs7tDQZpSGXbsNduYhs=
From: "gcc at octaforge dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/111129] New: std::regex incorrectly matches
 quantifiers with plus appended
Date: Thu, 24 Aug 2023 11:37:51 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: gcc at octaforge dot org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-111129-4@http.gcc.gnu.org/bugzilla/>
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: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111129

            Bug ID: 111129
           Summary: std::regex incorrectly matches quantifiers with plus
                    appended
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at octaforge dot org
  Target Milestone: ---

Example code:

```
#include <cstdio>
#include <string>
#include <regex>

int main(void) {
    std::smatch matches;
    auto re =3D std::regex(R"(a++)", std::regex::icase);
    std::string inp =3D "aaa";
    std::regex_search(inp, matches, re);
    for (auto &match: matches) {
        printf("%s\n", match.str().data());
    }
}
```

With libstdc++, this does not crash, and outputs 'aaa'.


This gives people a false idea that libstdc++ implements possessive quantif=
iers
(see e.g. https://github.com/wwmm/easyeffects/pull/2536) despite the
documentation or code having no references to any such extension (and the C=
++
standard likewise not mentioning it). You can verify that the semantics are=
 not
possessive by changing the pattern to 'a++a', which should with possessive
semantics not match anything, but with libstdc++ it's an identical match as
before.

With libc++, this correctly fails with: libc++abi: terminating due to uncau=
ght
exception of type std::__1::regex_error: One of *?+{ was not preceded by a
valid regular expression.=