Hi,
this is a test: https://godbolt.org/z/8PpX8W
On 03.02.20 10:07, J Decker wrote:
On Mon, Feb 3, 2020 at 12:23 AM aotto <aotto1968@xxxxxxxxxxx
<mailto:aotto1968@xxxxxxxxxxx>> wrote:
Hi,
there is an easy test, if Stefan is right and I'm wrong.
1. cast an INVALID Pointer to "aObj"
how would friend prevent an invalid pointer pass?
2. call "method_base(&aObj->obj,...)"
-> if stefan is right than "method_base" is called with an INVALID
aObj
as Pointer
-> if I am right than your software will CRASH :-)
given 1) sure, true in every case, doesn't make stephen wrong.
that is the reason why I require the "frienddef".
mfg AO
On 03.02.20 09:16, aotto wrote:
> Hi,
>
> Can someone confirm that *aObj->obj does NOT create any extray
"code"
> and does NOT do any
> POINTER resolution? -> if so than "gcc" already uses the "friend"
> logic I require :-)
https://godbolt.org/ this is a good place to collaborate on shared
code... it shows the generated assembly...
https://godbolt.org/z/X5mRYg is something resembling your case;
especially the function call of g()... I think probably an optimized
compile would generate the same for the assignments to tmp also...
So you just want to shortcut that the any first struct in a containing
pointer is valid as a parameter, and an implicit cast to the inner
type should be done? The internal browsing of what members are in a
type is not very convenient, and would require quite a few lines to
search...
struct a {
struct b {
struct c {
int d;
}C;
}B;
}A;
void g( struct c* pC ) {}
void h( struct b* pB) {}
void f(void){
g( &A ); // instead of g( &A.B.C );
h( &A ); // instead of h( &A.B );
}
>
> → I don't think that "gcc" do this already
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, ...)
------------------------
-----Ursprüngliche Nachricht-----
Von: aotto <aotto1968@xxxxxxxxxxx <mailto:aotto1968@xxxxxxxxxxx>>
Gesendet: Montag, 3. Februar 2020 09:02
An: Stefan Franke <stefan@xxxxxxxxx <mailto:stefan@xxxxxxxxx>>
Betreff: Re: AW: Feature request for "friendship" of pointers in "C"
This is not the same!
1. usually the aObj is a Pointer:
-> &aObj.obj => &(aObj->obj)
2. this DOUBLE indirect access creates definitely a CRASH if
aObj is invalid or freed
3. I use a internal a Pointer typecheck… where I can detect if
"my" pointer is valid or freed… but a "&(aObj->obj)" you
don't survive.
mfg
* Please reply at the bottom.
Ad 1: there is no need for '(' ')' if it's a pointer
&aObj->obj
Ad 2: this is not a double indirect access, the resulting address
is the
same as aObj as long obj is the first element of your struct, only
the
type changes
(void *)aObj == (void*)&aObj->obj
Ad 3: since the address is the same, your check will work.
Your issues aren't related to gcc - you might consider improving
your C
skills.
Cheers
Stefan
