CWG Issue 583 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-04-13

583. Relational pointer comparisons against the null pointer constant

Section: 7.6.9 [expr.rel]Status: CD3Submitter: James WidmanDate: 24 May 2006

[Moved to DR status at the April, 2013 meeting as paper N3624.]

In C, this is ill-formed (cf C99 6.5.8):

void f(char* s) {
    if (s < 0) { }
}

...but in C++, it's not. Why? Who would ever need to write(s > 0)when they could just as well write (s != 0)?

This has been in the language since the ARM (and possibly earlier); apparently it's because the pointer conversions (7.3.12 [conv.ptr]) need to be performed on both operands whenever one of the operands is of pointer type. So it looks like the "null-ptr-to-real-pointer-type" conversion is hitching a ride with the other pointer conversions.

Proposed resolution (April, 2013):

This issue is resolved by the resolution ofissue 1512.