🚀 go-pugleaf

We need to pass objects between a Mach-O application and a CFM shared
library, built from the same source code.

It seems that the Mach-O and CFM compilers behave differently with
regard to the alignment of derived classes, so that the object layout is
different.  Obviously this is a serious problem for us.

The following sample code illustrates the problem.  I don't understand
what the padding rules are here; CFM doesn't *always* pad so that the
derived class starts on the next 8-byte boundary, because if you comment
out the "int i" in Base, the offset of b2 is 1 on both compilers.

Is this a bug in one of the compilers?  Is there anything we can do to
work around this problem?  (We could manually pad all our classes to
multiples of 8 bytes, but this is very error-prone.)

(I have played with the various "#pragma options align=", but it doesn't
 seem to make a difference.)


#include <stdlib.h>  // for offsetof
#include <assert.h>

class Base
{
public:
  int i;
  bool b1;
};

class Derived : public Base
{
public:
  bool b2;
};

int main(void)
{
#ifdef __MACH__
    assert(offsetof(Derived,b2) == 5);
#else
    assert(offsetof(Derived,b2) == 8);
#endif

    return 0;
}


-- 
Stefan Haller
Berlin, Germany
http://home.snafu.de/stk/