RE: Differences in struct size when compiling C vs. C++

["Gonzalez, Inaky" <inaky.gonzalez@intel.com>]

> I think this is the same as in issue discussed a month ago on 
> the gcc ML 
> for classes (http://gcc.gnu.org/ml/gcc/2001-12/msg00836.html).
> Shortly:
> The empty struct sub-object must have a different address 
> from the struct 
> that contains it.
> This is obvious with A, where "int d" between the two makes 
> this happen 
> automatically.
> With B, the compiler must use an empty byte to let the struct 
> {} c addres 
> be different from that of B.

	Do you know if there is anyway then to do it? I have this data type,
and I template it:

template<class T>
struct A
{
  int a;
  int b;
  T c;
};

The idea is T is normally a class that offers an interface like:

struct T1
{
  void fn1 (void);
  void fn2 (void);
 private:
  // data members
};

And sometimes it is like:

struct T2
{
  static void fn1 (void);
  static void fn2 (void);
  // no data members, stateless
}

So, I want struct A<T> to be minimal size (8 bytes) when I am using T2 [as
it in theory should be] and to be whatever it has to be if it is T1. Note
there is no runtime discovery of types implied here, as it is all know at
compile time (love templates :).

I would expect that being that empty struct, it'd be optimized out by the
compiler, so I can use the same interface w/o the size penalty, but looks
like GCC thinks differently. Maybe there is a way to trick it ...


Iñaky Pérez González -- (503) 677 6807
I do not speak for Intel Corp, opinions are my own.