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


277. Zero-initialization of pointers

Section: 9.4  [dcl.init]     Status: CD1     Submitter: Andrew Sawyer     Date: 5 Apr 2001

[Moved to DR at 10/01 meeting.]

The intent of 9.4 [dcl.init] paragraph 5 is that pointers that are zero-initialized will contain a null pointer value. Unfortunately, the wording used,

...set to the value of 0 (zero) converted to T

does not match the requirements for creating a null pointer value given in 7.3.12 [conv.ptr] paragraph 1:

A null pointer constant is an integral constant expression (7.7 [expr.const]) rvalue of integer type that evaluates to zero. A null pointer constant can be converted to a pointer type; the result is the null pointer value of that type...

The problem is that the "value of 0" in the description of zero-initialization is not specified to be an integral constant expression. Nonconstant expressions can also have the value 0, and converting a nonconst 0 to pointer type need not result in a null pointer value.

Proposed resolution (04/01):

In 9.4 [dcl.init] paragraph 5, change

...set to the value 0 (zero) converted to T;

to

...set to the value 0 (zero), taken as an integral constant expression, converted to T; [footnote: as specified in 7.3.12 [conv.ptr], converting an integral constant expression whose value is 0 to a pointer type results in a null pointer value.]