On Mon, Mar 09, 2020 at 12:41:37PM -0400, Aaron Ballman wrote: > > You could view NULL as a special pointer pointing to an inaccessible > > zero sized object. Adding 0 to it still points to the same special > > non-object. I guess that is how the C++ folks see it. > > This wording has always been UB in C. It stopped being UB in C++20 but > was UB prior to that. I did not see a core issue pertaining to this > (though it's possible I've missed it -- the C++ core issues list is a > bit hard to track these days), so I am not certain why this change was > made so recently.
AFAICT it has always been well defined in C++, though the wording changed a bit. In C++11 (n3337) it is 5.7 note 7: "If the value of 0 is added or subtracted from a pointer value, the result compares equal to the original pointer value." Same text but moved one note down to 8 in n3797 (C++14). N4659 (C++17) makes it explicit for NULL pointers in 8.7 note 7 (as Taylor cited earlier in this thread): "If the value 0 is added or subtracted from a null pointer value, the result is a null pointer value." Martin
