[Bug c++/16618] New: In C++, offsetof fails with constant member

["jrh5y6virbl36ay at optonline dot net" <gcc-bugzilla at gcc dot gnu dot org>]

gcc-3.4.1, Linux kernel 2.4.26, glibc-2.3.2.  Configured with:
../gcc-3.4.1/configure --prefix=/opt/gcc-3.4.1 --enable-threads
--with-system-zlib --enable-__cxa_atexit --with-cpu=pentium4
--with-arch=pentium4 --with-tune=pentium4

This code:

#include <cstddef>

struct test
{
  const char a;
};

int main(int argc, char *argv[])
{
  size_t n=offsetof(test,a);
}

Leads to:

$ c++ -c 040718a.cc
040718a.cc: In function `int main(int, char**)':
040718a.cc:10: error: reinterpret_cast from type `const char*' to type `char*'
casts away constness

The preprocessor output:

# 1 "040718a.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "040718a.cc"
# 1
"/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/../../../../include/c++/3.4.1/cstddef"
1 3
# 46
"/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/../../../../include/c++/3.4.1/cstddef"
3
       
# 47
"/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/../../../../include/c++/3.4.1/cstddef"
3

# 1 "/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/include/stddef.h" 1 3 4
# 151 "/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/include/stddef.h" 3 4
typedef int ptrdiff_t;
# 213 "/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/include/stddef.h" 3 4
typedef unsigned int size_t;
# 49
"/opt/gcc-3.4.1/lib/gcc/i686-pc-linux-gnu/3.4.1/../../../../include/c++/3.4.1/cstddef"
2 3

namespace std
{
  using ::ptrdiff_t;
  using ::size_t;
}
# 2 "040718a.cc" 2

struct test
{
  const char a;
};

int main(int argc, char *argv[])
{
  size_t n=(__offsetof__ (reinterpret_cast <size_t> (&reinterpret_cast <char &>
(static_cast<test *> (0)->a))));
}

-- 
           Summary: In C++, offsetof fails with constant member
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P1
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jrh5y6virbl36ay at optonline dot net
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16618