[Bug c++/36549] New: offsetof defined as function in contravention of ISO/IEC 14882:1998 17.4.1.2 para 5

["ajrobb at bigfoot dot com" <gcc-bugzilla at gcc dot gnu dot org>]

>Class:         rejects-legal
>Release:       gcc (GCC) 4.2.3
>Description:
like bug 14932 - 4.2.3 c++ does not allow variable array index in macro
offsetof

it looks like offsetof maps to a builtin function:
#define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)

This appears to be in contravention of ISO/IEC 14882:1998 17.4.1.2 para 5:

"Names which are defined as macros in C shall be defined as macros in the C++
Standard Library, even if C grants license for implementation as functions.
[Note: the names defined as macros in C include the following: assert, errno,
offsetof, setjump, va_arg, va_end and va_start. -end note]"

>How-To-Repeat:

#include <cstddef>
struct A {
int array[10];
};

std::size_t off(int x) { return offsetof(struct A, array[x]); }

$ g++ offsetof.cc -S
offsetof.cc: In function 'size_t off(int)':
offsetof.cc:7: error: 'x' cannot appear in a constant-expression
$ cat offsetof.s
      .file   "offsetof.cc"

>Fix:

use a macro (as mandated for c++) - e.g. /usr/include/iso/stddef_iso.h:
#define   offsetof(s, m)  (std::size_t)(&(((s *)0)->m))


-- 
           Summary: offsetof defined as function in contravention of ISO/IEC
                    14882:1998 17.4.1.2 para 5
           Product: gcc
           Version: 4.2.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ajrobb at bigfoot dot com
 GCC build triplet: i386-pc-solaris2.10
  GCC host triplet: i386-pc-solaris2.10
GCC target triplet: i386-pc-solaris2.10


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36549