Re: A: a new bug to old plain C

Hi there!

Either the links you've provided or the links you provided earlier
(yesterday) are irrelevant, cause they are just discussing if it is safer
to convert "Foo_Type **" to "const Foo_Type **" or not.

Once again, we are not converting "char** to const char**", we're
converting char** to const char * const * const".
And we're not discussing if it is safer or not, we are discussing GCC
compiler error.


Respectfully,
Aleksandr G Povaliaev.


вс, 23 нояб. 2025 г. в 11:13, Jonathan Wakely <[email protected]>:

>
>
>
> On Sun, 23 Nov 2025, 03:19 Александр Поваляев, <[email protected]>
> wrote:
>
>> Hi there!
>>
>> And again, we are not talking about warnings, some compilers show an
>> error (so, it just stops compiling), some not.
>>
>
> Yes, I understand that. GCC gives an error because the code violates the
> rules of the C standard:
> https://cigix.me/c23#6.5.17.2
>
> There is an example in the C standard explicitly saying that the pointer
> conversion from char** to const char** violates a constraint:
> https://cigix.me/c23#6.5.17.2.p6
>
> The C standard requires a diagnostic for a constraint violation:
> https://cigix.me/c23#5.1.1.3.p1
>
>
>> I believe it should be fixed, because there is a quite evident use-case
>> when using "const Foo * const * const"  is in the order.
>>
>> And it is also quite in accordance with the recommendations given (links
>> mentioned says "don't use const Foo **, cause it might be dangerous").
>> And what we're doing is not using "const Foo**". We tend to use "const
>> Foo * const * const" instead.
>>
>> "const" is one of the cornerstones of C language, which prevents possible
>> errors and makes programming safer.
>>  So, it should be handled appropriately.
>>
>
> It is handled according to the C standard.
>
> I'm sorry you are unable to accept this, but I'm not going to waste any
> more time replying in this thread.
>
>
>
>
>> Respectfully,
>> Aleksandr G Povaliaev.
>>
>> сб, 22 нояб. 2025 г. в 21:37, Jonathan Wakely <[email protected]>:
>>
>>>
>>>
>>> On Sat, 22 Nov 2025, 15:18 Александр Поваляев, <[email protected]>
>>> wrote:
>>>
>>>> Hi there!
>>>>
>>>> The links you posted are all about "Don't use Foo** → const Foo**, use const
>>>> Foo** to const Foo* const* conversion instead"
>>>> (https://isocpp.org/wiki/faq/const-correctness#constptrptr-conversion,
>>>> https://c-faq.com/ansi/constmismatch.html).
>>>> Also, it is being discussed if it is safe or not to use such kind of
>>>> conversion.
>>>>
>>>> But we don't use "Foo** -> const Foo**" conversion anyhow.
>>>> We use "Foo** -> const Foo * const * const" conversion. So, we just
>>>> follow the recommendation given and not the opposite. :)
>>>>
>>>
>>>
>>> And so your code would compile in C++.
>>>
>>> But like it says in the C FAQ, the rules for C and C++ are different. C
>>> does not allow that conversion, even though it would be safe (and C++ does
>>> allow it).
>>>
>>> Here is the relevant part:
>>>
>>> "C++ has more complicated rules for assigning const-qualified pointers
>>> which let you make more kinds of assignments without incurring warnings,
>>> but still protect against inadvertent attempts to modify const values. C++
>>> would still not allow assigning a char ** to a const char **, but it would
>>> let you get away with assigning a char ** to a const char * const *.)"
>>>
>>>
>>>
>>>
>>>
>>>> Anyway some compilers return an error. And this is not the expected
>>>> behaviour for use. It is A BUG!!!
>>>>
>>>
>>> OK, maybe try a different compiler then.
>>>
>>>
>>>
>>>
>>>>
>>>>>>
>>>>>>