Feature request for "friendship" of pointers in "C"

[Holger Lamm]

Hi,

Am 02.02.20 um 08:44 schrieb aotto:
> Hi, the following scenario has a "definition hole" in the "C" language
>
> code example:
>
> -------------------------
> struct base {
>   ...
> };
>
> struct A {
>   struct base obj;
>   ...
> } aObj;
>
> struct B {
>   struct base obj;
>   ...
> } bObj;
>
> void method_base (struct base * hdl, ...);
>
> method_base(&aObj, ...)
> method_base(&bObj, ...)
> ------------------------
>
> - a POINTER to "A" is also a valid POINTER to "base"
> - a POINTER to "B" is also a valid POINTER to "base"

No. The order of elements of structures in memory is implementation 
defined and not guaranteed to be the order of enumeration in the definition.
The ONLY valid and portable way to express the call is

   method_base(&aObj.obj, ...)
   method_base(&bObj.obj, ...)

> - a POINTER to "base" is NOT a valid POINTER to "A" and "B"

of course not. It is a pointer to one element within a structure, not to 
the structure itself.

Just my 2 cents,
Holger