Issue 0097: Can the type argument of the offsetof macro be an incomplete type?

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: Ron Guilmette, WG14
Date: 1993-12-03
Submitted against: C90
Status: Closed
Cross-references: 0040.06
Converted from: dr.htm, dr_097.html

ANSI/ISO C Defect report #rfg4:

Subclause 7.1.6 fails to contain any constraint which would prohibit the type argument given in an invocation of the offsetof macro from being an incomplete type. This situation can arise in examples such as the following:

#include <stddef.h>

 struct S
        {
        int member1;
        int member2[1+offsetof(struct S, member1)];
        };

I believe that a constraint prohibiting the type argument to offsetof from being an incomplete type is clearly needed.

This problem could be solved by adding an explicit constraint to subclause 7.1.6, such as:

The type argument given in an invocation of the offsetof macro shall be the name of a complete structure type or a complete union type. (Note that this way of expressing the constraint also makes it completely clear that diagnostics are required for cases where the type given in the invocation is, for instance, a function type, an array type, an enumerated type, a pointer type, or a built-in arithmetic type.)

Comment from WG14 on 1997-09-23:

Response

See the response to Defect Report #040, question 6. This code is not strictly conforming.