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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/102918] Undefined behaviour in regex header
 (uininitialized boolean)
Date: Mon, 25 Oct 2021 08:48:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102918

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-10-25
             Status|UNCONFIRMED                 |WAITING

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
std::sub_match only has one constructor, and it initializes the bool. The o=
nly
stores to that variable are literal treu or false values, or the result of a
boolean expression first !=3D last. So there's no way I can see for the lib=
rary
to cause this behaviour Are you sure you're not causing undefined behaviour=
 in
your own code?

Have you tried building with -D_GLIBCXX_DEBUG to get runtime checks in
std::match_results.

Without more details there's nothing we can do here. The <regex> code looks
correct.=