https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109891
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:
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 == NULL) s = "(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=6518 .
