🚀 go-pugleaf

In article <4dns28$3c5@boy.nmd.msu.ru>,
Alexander Krotoff <krotoff@such.srcc.msu.su> wrote:
>X-InCommentTo: john@polo.demon.co.uk (John Winters)
>
>john@polo.demon.co.uk (John Winters) wrote:
>> In article <KANZE.96Jan17121659@slsvewt.lts.sel.alcatel.de>,
>> James Kanze US/ESC 60/3/141 #40763 <kanze@lts.sel.alcatel.de> wrote:
>> [snip]
>> >
>> >Originally, the C standard was going to allow this; in fact, it was
>> >going to allow all casts which added const anywhere in the type.  Then
>> >someone pointed out that the conversion 'char ** -> char *const *' was
>> >unsafe.  As a result, the wording was changed to only allow adding the
>> >const at the top level.
>> 
>> Interesting.  Could you enlighten us (well, me anyway) as to *why* it
>> is unsafe.  I don't find it immediately obvious.
>
>Hello Joshn.

Who he?

>
>here is an example Joe Buck sent me this Julay.
>i did not understand it too before.
>
[snip]
>
>#include <iostream.h>
>
>int main() {
>    const char ** const_ch_pp;
>    char * ch_p;
>    char ** ch_pp = & ch_p;
>    const char const_ch = 'a';
>    const char * const_ch_p = &const_ch;
>
>    cout << "const_ch_p points to " << *const_ch_p << endl;
>    const_ch_pp = ch_pp;        // illegal, but you want it legal
>    *const_ch_pp = const_ch_p;  // copy const ptr to non-const ptr
>    *ch_p = 'b';                // now we can change the const object
>    cout << "const_ch_p points to " << *const_ch_p << endl;
>}
>

Funny, I could have sworn it said comp.std.c on the door.

>It's simply not debatable: it is unsafe to assign a char** to a const char**.
>--------------------------------------------------------------------

Yes, I understand now.  I go to sleep explaining it to myself. :-)

John
-- 
John Winters.  Wallingford, Oxon, England.