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From: "mimomorin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/109891] New: Null pointer special handling in
 ostream's operator << for C-strings
Date: Wed, 17 May 2023 14:20:25 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109891

            Bug ID: 109891
           Summary: Null pointer special handling in ostream's operator <<
                    for C-strings
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mimomorin at gmail dot com
  Target Milestone: ---

This code

    #include <iostream>
    int main() { std::cout << (char*)nullptr; }

does not cause any bad things (like SEGV), because libstdc++'s
operator<<(ostream, char const*) has special handling of null pointers:=20

    template<typename _CharT, typename _Traits>
    inline basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
    {
        if (!__s)
            __out.setstate(ios_base::badbit);
        else
            __ostream_insert(...);
        return __out;
    }

Passing a null pointer to this operator is a precondition violation, so the
current implementation perfectly conforms to the C++ standard. But, why don=
't
we remove this special handling? By doing so, we get
- better interoperability with toolings (i.e. sanitizers can find the bug
easily)
- unnoticeable performace improvement
and we lose
- deterministic behaviors (of poor codes) on a particular stdlib
I believe the first point makes more sense than the last point.

It seems that old special handling `if (s =3D=3D NULL) s =3D "(null)";`
(https://github.com/gcc-mirror/gcc/blob/6599da0/libio/iostream.cc#L638) was
removed in GCC 3.0, but reintroduced (in the current form) in GCC 3.2 in
response to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D6518 .=