This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2023-01-15


2606. static_cast from "pointer to void" does not handle similar types

Section: 7.6.1.9  [expr.static.cast]     Status: CD6     Submitter: Richard Smith     Date: 2022-06-28

[Accepted at the July, 2022 meeting.]

Consider:

  struct S {
    int a[5];
  } s;
  int (*p)[] = reinterpret_cast<int(*)[]>(&s);
  int n = (*p)[0];

This ought to have defined behavior: a pointer to s and a pointer to s.a are pointer-interconvertible, so you should be able to navigate between them this way. But the cast as shown does not work, because the type of the pointer-interconvertible object is int[5], not int[].

Proposed resolution (approved by CWG 2022-07-01):

Change in 7.6.1.9 [expr.static.cast] paragraph 13 as follows:

... Otherwise, if the original pointer value points to an object a, and there is an object b of type similar to T (ignoring cv-qualification) that is pointer-interconvertible (6.8.4 [basic.compound]) with a, the result is a pointer to b. Otherwise, the pointer value is unchanged by the conversion.