CWG Issue 1865 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-11-05

1865. Pointer arithmetic and multi-level qualification conversions

Section: 7.6.6 [expr.add]Status: CD4Submitter: Geoffrey RomerDate: 2014-02-15

[Moved to DR at the November, 2014 meeting.]

The resolution of issue 1504 added 7.6.6 [expr.add] paragraph 7:

For addition or subtraction, if the expressions P or Qhave type “pointer to cv T”, where Tis different from the cv-unqualified array element type, the behavior is undefined.

This wording was intended to address derived-base conversion in pointer arithmetic, but it inadvertently categorized as undefined behavior previously well-defined pointer arithmetic on pointers that are the result of multi-level qualification conversions. For example:

void f() { int i = 0; int* arr[3] = {&i, &i, &i}; int const * const * aptr = arr; assert(aptr[2] == &i); }

This now has undefined behavior because the type of *aptr is “pointer to const int,” which is different from the cv-unqualified array element type, “pointer to int.”

See also issue 330.

Proposed Resolution (July, 2014):

Change 7.6.6 [expr.add] paragraph 7 as follows:

For addition or subtraction, if the expressions Por Q have type “pointer to cv T”, where T is different from the cv-unqualified and thearray element type are not similar (7.3.6 [conv.qual]), the behavior is undefined. [Note: In particular, a pointer to a base class cannot be used for pointer arithmetic when the array contains objects of a derived class type. —_end note_]