invalid offsetof from non-POD type

["Chris Croswhite" <ccroswhite at get2chip dot com>]

Hello all,

Perhaps someone could give me had with understanding this error:
"foo.c:15: warning: invalid offsetof from non-POD type `struct foo_struct';
use pointer to member instead"

Here is the simplest test:

#include <stdio.h>
#include <linux/stddef.h>

class Myclass {
          int _val;
};

struct foo_struct {
          Myclass a;
          void *bar;
};

int main(void)
{
          printf("offset is %d\n", offsetof(struct foo_struct, bar));
}


The class within the struct is causing offsetof warning.  Could someone
describe why this is a warning and if this produces invalid code.  If this
is correect code, is there a way to turn off this warning?

TIA,
Chris