about address...

[s88]

Hi all:
I saw a code slice
<code>
&(((structure *)0)->m)
</code>
Looks like to identified the address of the element in the structure.
Could U explain that the meanning of the 0???

Thanx!!

 

[Suman]

Hi all:
I saw a code slice
<code>
&(((structure *)0)->m)

Looks close to an implementation of offsetof macro. For further
details look at Jack Klein's excellent post here:
<http://groups.google.co.in/group/comp.lang.c/browse_frm/

thread/53b5e085cd53d9d9/dd6a40ce090ec975?q=offsetof&rnum=5#dd6a40ce090ec975>

 

[Emmanuel Delahaye]

s88 a écrit :

I saw a code slice
<code>
&(((structure *)0)->m)
</code>
Looks like to identified the address of the element in the structure.
Could U explain that the meanning of the 0???

This is a complicated way of writing

<code>
#include <stddef.h>

<...> offsetof(structure, m);

</code>

Do you really need to know about the gory details ?

 

[pemo]

Hi all:
I saw a code slice
<code>
&(((structure *)0)->m)
</code>
Looks like to identified the address of the element in the structure.
Could U explain that the meanning of the 0???

Zero is being cast to a 'structure *' - it'd interesting to see structure,
and what 'm' is.

 

[Mockey Chen]

Does this idiom portable?
I means compile ok and run correctly on every platform and compiler.

 

[Emmanuel Delahaye]

Mockey Chen a écrit :

[Please don't top-post. Fixed]

> Is this idiom portable?
> I means compile ok and run correctly on every platform and compiler.

Yes it has belonged to the C-language since 1989.

 

[Keith Thompson]

Does this idiom portable?
I means compile ok and run correctly on every platform and compiler.

Every conforming C implementation supports the offsetof() macro.

The code slice above is not portable. It's one possible
implementation of offsetof().