[Bug libstdc++/105580] [13/14/15/16 Regression] warning "potential null pointer dereference" raised when using istreambuf_iterator and any "-O" flag

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105580

--- Comment #14 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tomasz Kaminski <tkaminsk@gcc.gnu.org>:

https://gcc.gnu.org/g:bfc2b87f8244a13ab00e8e3fe2af1d6d18fcaa36

commit r16-7844-gbfc2b87f8244a13ab00e8e3fe2af1d6d18fcaa36
Author: Tomasz KamiÅski <tkaminsk@redhat.com>
Date:   Fri Feb 27 20:14:44 2026 +0100

    libstdc++: Add #pragma to slience null-dereference warning in
istreambuf_iterator::operator++ [PR105580]

    The warning was produced by following sequence, given an
istream_iterator<char>
    it, such that *it will result in hitting EoF in it->_M_get(), and thus
clearing
    _M_sbuf, the subsequent call to ++it, will result in _M_sbuf->sbumpc() call
on
    null pointer. This is however an false-positive, as in such situation
    it == istream_iteator() returns true, and the iterator should not be
    incremented in first place.

    This patch sliences the issue, by disabling the "-Wnull-dereference" using
    GCC diagnostic pragmas. To work correctly the pragmas needs to be placed
around
    streambuf functions on which the issue originating from istreambuf_iterator
are
    reported.

            PR libstdc++/105580

    libstdc++-v3/ChangeLog:

            * include/std/streambuf (streambuf::gptr, streambuf::egptr)
            (streambuf::gbump): Surround with pragma disabling
-Wnull-dereference.
            * testsuite/24_iterators/istreambuf_iterator/105580.cc: Remove
check for
            warning being emitted.

    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Tomasz KamiÅski <tkaminsk@redhat.com>