Re: On alignment

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Jason Merrill <jason at redhat dot com> writes:

| On 23 Apr 2003 12:11:24 -0600, Tom Tromey <tromey at redhat dot com> wrote:
| 
| >>>>>> "Jason" == Jason Merrill <jason at redhat dot com> writes:
| >
| > [ about  struct foo { double x; } ]
| >
| > Tom> I'd like to find the most future-proof way to do this.  In the above,
| > Tom> is __alignof__(foo::x) the best way?  I'm only concerned with
| > Tom> alignment of fields.
| >
| > Jason> It is since my recent patch to do all alignment calculation for
| > Jason> fields in layout_decl.
| >
| > I can't do this.
| >
| >     struct aligner { double field; };
| >
| >     int compute () { return __alignof__ (aligner::field); }
| 
| Ah, no, you need to do something like
| 
| #define FIELD_ALIGNOF(TYPE) __alignof (((struct { TYPE t; } *)0)->t)

Hmm, when tested like

    #include <iostream>

    #define FIELD_ALIGNOF(TYPE) __alignof (((struct { TYPE t; } *)0)->t)

    int main()
    {
       std::cout << FIELD_ALIGNOF(double) << std::endl;
    }

I get:

    j.C: In function `int main()':
    j.C:7: error: types may not be defined in casts

I think the template-based solution I posted in another message solves
the problem...  

-- Gaby