cannot bind packed field error

[Christoph Bartoschek]

Am Dienstag, 2. Mai 2006 20:40 schrieb Andrew Haley:
> Christoph Bartoschek writes:
>  > Am Dienstag, 2. Mai 2006 17:28 schrieb John Love-Jensen:
>  > > > Is this an error in the compiler or is there a mistake in the code?
>  > >
>  > > I think (but I'm not sure) that it is a mistake in the code.
>  > >
>  > > In that the alignment and packing constraints of a.b.c are different
>  > > from a plain old int& and int const&.
>  >
>  > But why does the call to  func(int const &) succeed, if I remove the
>  > other func function?
>
> Because the compiler doesn't know what you're trying to do.  Let's say
> that you intended to modify the packed field.  Clearly the compiler
> can't do that, as a packed int isn't compatible with an int.  So what
> would you rather have?  A compile-time error, or the compiler silently
> call func(int const &) instead?

You are right that a compile-time error is better in this case, but why don't 
I get a comile-timer error, if I use pointers instead of references? They 
should be nearly the same:

#include <iostream>

struct A {
  union {
    int  c;
  } b;
} __attribute__ ((packed));

void func(int const *) {}
void func(int * p) {
        std::cout << *p << std::endl;
        *p = 12;
}

int main()
{
   A a;

   a.b.c = 2;

   func(&a.b.c);
   std::cout << a.b.c << std::endl;
}


Christoph