struct named 0

[Mohd Hanafiah Abdullah]

Is the following code conformat to ANSI C?

typedef struct {
int a;
int b;
} doomdata;

int main(void)
{
int x;

x = (int)&((doomdat a*)0)->b;
printf("x=%d\n" , x);
return x;
}

The part,
(int)&((doomdat a*)0)->b;

is it conformant to ANSI C? What is it supposed to do?

Thanks for any tips.

Napi

--
http://www.axiomsol.com
http://www.cs.indiana.edu/hyplan/napi.html

[Richard Bos]

Christian Bau <ch***********@ cbau.freeserve. co.uk> wrote:

In article <31************ *@individual.ne t>,
"S.Tobias" <si***@FamOuS.B edBuG.pAlS.INVA LID> wrote:

Richard Bos <rl*@hoekstra-uitgeverij.nl> wrote:

Christian Bau <ch***********@ cbau.freeserve. co.uk> wrote:
> C99 Final Draft:
>
> 6.5.9.2 Equality operators/constraints. "one operand is a pointer and
> the other is a null pointer constant"
>
> 6.5.15.3 Conditional operator/constraints: "One of the following shall
> hold for the second and third operands: " ... "one operand is a pointer
> and the other is a null pointer constant"
>
> 6.5.16.1 Simple assignment/constraints: "the left operand is a pointer
> and the right is a null pointer constant"

That's not a list given by the Standard, that's a list of somewhat
related quotations from the Standard given by you. Of course, it's
incomplete.
You could do us all a favour and tell us what is missing.

I don't think so. First of all because there is no definitive list, and
the normative text is quite simple to understand: _whenever_ a null
pointer constant appears in a pointer context, no matter whether there
is an explicit mention of it elsewhere in the Standard as well, it is
translated to a null pointer. That's all. Really, that's the whole
story. No list need be involved.
And the second reason is that if I now give a list of what I think are
all mentions of pointer contexts in the Standard, I am clearly
guaranteed to miss one. Hah.
But I'll mention one that you did miss: an explicit cast. Which is what
caused all this discussion.
Besides that those quotes are taken from Constraints.

Of course they are. The Standard defines operators, and then under
"Constraint s" it gives a list of all the operand combinations that are
allowed.

Yes. Thus demonstrating nicely why grep is no substitute for reading the
Standard yourself.

Richard