offsetof() operator. A tricky question.

[amos shapira]

vohra at uts.amdahl.com (Pavan Vohra) writes:

>I would like to compile in the offsets of structure members.

>For example, with this structure

>    struct astruct {
>      int member0;
>      char member1;
>    } myastruct;

>I want to have, in the same program that the structure appears in,
>the number of bytes past myastruct where I can find member1.

The answer could be simple and I used several times, do this:

struct astruct *ap;

ap = NULL;

offsetof_member0 = &ap->member0; /* zero offset */
offsetof_member1 = &ap->member1; /* sizeof(member0) */

An offsetof() operator would be quite handy here. But until then you can
use this with a good portability of your programs.

Now comes to mind, maybe you could avoid the nbull pointer variable with this
(didn't try it):

offsetof_member0 = &((struct astruct *)NULL->member0);
offsetof_member1 = &((struct astruct *)NULL->member1);

- Amos Shapira

amoss at batata.bitnet
amoss at batata.huji.ac.il