Taking address of array

[Marc Auslander]

In article <1991Apr9.172534.28982 at tcom.stc.co.uk> graham at tcom.stc.co.uk (Graham Bardsley) writes:


>I've got some macros which calculate the address of an offset of a structure
>(stolen from the X11R4 src), and some of the structures I'm using them have
>character arrays:

>struct small_struct
>{
>	int x;
>	char y[100];
>};

>What I want to know is, if the macro calculates:

>((int) (((char *) (&(((struct small_struct*) 0)->y))) - ((char *) 0)))

>Is the value of this a valid construct which will calculate the offset of y on 
>most traditional C compilers, since on the standard Sun C compiler it throws 
>out the warning: 

>	& before array or function: ignored

The Risc System/6000 compiler also issues a warning message and
compiles.  

Note that if you have a macro which takes addresses of things and you
need to pass it an array, a work around is to pass the first element.
In your example:

 ((int) (((char *) (&(((struct small_struct*) 0)->y[0]))) - ((char *) 0)))

is correct C.
--


Marc Auslander       <marc at ibm.com>