Re: A: a new bug to old plain C

Please stop. It's invalid C, C is not C++, and you have been told as much by several people. Please stop spamming everyone on the mailing list with uninformed bickering :/

-------- Original Message --------
On 25/11/2025 16:10, Александр Поваляев via Gcc-help <[email protected]> wrote:

>  Hi there!
>  
>  My code snippet which we're discussing was written in accordance with the
>  code safety recommendations provided by your colleagues :)
>  So, the code snipped is naturally doing what was recommended in that C FAQ:
>  we're converting "Foo**" to "const Foo * const *" to avoid the possible
>  const-violations.
>  
>  Here is a note from some recommendation which has been provided by your
>  colleagues (
>  https://isocpp.org/wiki/faq/const-correctness#constptrptr-conversion) :
>  "The rationale for why that error is a good thing is given below. But
>  first, here is the most common solution: *simply change **const
>  Foo** to const Foo* const**"
>  And we are NOT converting "Foo**" to "const Foo**", we ARE converting
>  "Foo**" to "const Foo * const * const".
>  Please pay some more attention to what I am writing here.
>  
>  Then one more "const" is added since it is going to change neither the
>  value which the variable is pointing to nor the value of the variable
>  itself, since it denotes "end-of-loop iteration".
>  Please, read carefully the use-case which I provided at the very beginning
>  of this e-mail thread. Here it is:
>  "
>  struct zzz const * const * const end_of_arr = arr_of_ptr + count;
>  "
>  And it should work fine. Since it is written in all the recommendations and
>  in accordance to C standard.
>  Nobody and no place and no recommendation forbid us from converting "Foo**"
>  to "const Foo * const * const".
>  So, since it is allowed by C standard, it should work fine with all the GCC
>  toolchains.
>  But with some of them, some of GCC toolchains (like GCC ARM trunk linux) it
>  doesn't.
>  So, it should be fixed.
>  
>  Respectfully,
>  Aleksandr G Povaliaev.
>  
>  
>  
>  вт, 25 нояб. 2025 г. в 14:58, Matthias Pfaller <[email protected]>:
>  
>  > As several people already pointed out to you, this is not a bug in the
>  > compiler. Your code is valid with C++, but invalid with C.  Is this so hard
>  > to understand? What you do is just like insisting on
>  >
>  > void f(int *);
>  > void nonsense(void)
>  > {
>  >   register int x;
>  >   f(&x);
>  > }
>  >
>  > to be valid C code. It might look ok, but it's still invalid code.
>  >
>  > On 2025-11-25 12:28, Александр Поваляев wrote:
>  >
>  > Hi there!
>  >
>  > Yes.
>  > Here is the original message from myself: "
>  > struct zzz {
>  > unsigned x, y;
>  > };
>  > void square(struct zzz ** arr_of_ptr, unsigned count) {
>  > *// The first "const" produce an error (not a warning) within some GCC
>  > toolchains, for example ARM GCC trunk (linux), see goldbolt.org
>  > <http://goldbolt.org>*
>  > struct zzz const * const * const end_of_arr = arr_of_ptr + count;
>  > *// Without the first const "struct zzz * const * const end_of_arr =
>  > arr_of_ptr + count;" it works fine!!!*
>  > }
>  > ".
>  >
>  > So, somebody made this BUG to some GCC toolchains (ARM GCC trunk(linux)
>  > and some others). We need to have it nailed down and fixed somehow.
>  >
>  > Respectfully,
>  > Aleksandr G Povaliev.
>  >
>  >
>  > вт, 25 нояб. 2025 г. в 13:32, Matthias Pfaller <[email protected]>:
>  >
>  >> You are aware, that you are quoting the C++-FAQ? Aren't we talking about
>  >> C?
>  >>
>  >> Congratulations btw, you are (I think) the first person managing to
>  >> exhaust
>  >> Jonathan's patience. I always thought he had a limitless source of
>  >> patience hidden
>  >> somewhere and envied him for it...
>  >>
>  >> On 2025-11-25 11:24, Александр Поваляев via Gcc-help wrote:
>  >> > We're not converting "Foo** -> const Foo**". We are doing "Foo** ->
>  >> const
>  >> > Foo * const * const" conversion and this works fine (according to the
>  >> right
>  >> > the same
>  >> > https://isocpp.org/wiki/faq/const-correctness#constptrptr-conversion
>  >> which
>  >> > was mentioned).
>  >> >
>  >> > So, what we're doing is correct from both language syntax and coding
>  >> > practices (safe coding) points of view.
>  >> > This bug should be reported and fixed!!!
>  >> >
>  >> > Respectfully,
>  >> > Aleksandr G Povaliaev.
>  >> >
>  >> > пн, 24 нояб. 2025 г. в 20:49, Henrik Holst <
>  >> [email protected]>:
>  >> >
>  >> >> no they are not, they are a WIKIfication of the C specification, in
>  >> >> particular the heading "Why am I getting an error converting a Foo** →
>  >> >> const Foo**?" in an official FAQ from the C Standards Committee should
>  >> make
>  >> >> you realize this.
>  >> >>
>  >> >> /HH
>  >> >>
>  >> >> Den mån 24 nov. 2025 kl 18:45 skrev Александр Поваляев <
>  >> >> [email protected]>:
>  >> >>
>  >> >>> The articles mentioned are all about coding practices ("safe" and
>  >> >>> "unsafe"). They are not about bugs in compilers and hard restrictions
>  >> being
>  >> >>> placed on where I can use "const" in my code and where I can't. :)
>  >> >>>
>  >> >>> The links mentioned earlier just give a recommendation to use "Foo**
>  >> ->
>  >> >>> const Foo * const *" conversion instead of "Foo** -> const Foo**".
>  >> >>> Literally, what I am saying is that: "if you can use const, you should
>  >> >>> use it". And this is the case which just confirms my attitude.
>  >> >>> But again, this is about coding practices and recommendations. There
>  >> is
>  >> >>> no place in C and C++ standards saying "DON"T USE CONST EVEN IF YOU
>  >> CAN DO
>  >> >>> IT. WE'RE PROHIBITING THIS".
>  >> >>>
>  >> >>> And so, what GCC compiler (+ some SDKs) is doing now is just the
>  >> opposite
>  >> >>> to the recommendation mentioned. It restricts the places where "const"
>  >> >>> might be used.
>  >> >>> Anyway, it is a BUG (BIG BUG!!!) in the GCC + SDK. And the BUG was not
>  >> >>> made intentionally to protect software engineers from using "unsafe
>  >> coding
>  >> >>> practices" :)))))
>  >> >>> For such kind of practices, there are warnings with information
>  >> messages.
>  >> >>> And the bug in GCC should be (1) reported; (2) nailed down and (3)
>  >> fixed.
>  >> >>>
>  >> >>> Respectfully,
>  >> >>> Aleksandr G Povaliaev.
>  >> >>>
>  >> >>>
>  >> >>> пн, 24 нояб. 2025 г. в 16:10, Henrik Holst <
>  >> [email protected]
>  >> >>>> :
>  >> >>>>
>  >> >>>> Den mån 24 nov. 2025 kl 13:40 skrev Александр Поваляев <
>  >> >>>> [email protected]>:
>  >> >>>>
>  >> >>>>> Hi there!
>  >> >>>>>
>  >> >>>>> "False sense of security". Const is a hint to any C compiler to make
>  >> >>>>> code more error-prone. So, it is always better to use as much
>  >> "const" as
>  >> >>>>> possible.
>  >> >>>>> My point is that "if const might be used, it SHOULD be used". That
>  >> is
>  >> >>>>> the cornerstone.
>  >> >>>>> I want to use it, so GCC compiler + SDK should make it possible. It
>  >> is
>  >> >>>>> my code and my design decisions being undertaken.
>  >> >>>>>
>  >> >>>>> All discussions if it is possible to overcome or not "Const"
>  >> >>>>> restriction is irrelivant here.
>  >> >>>>>
>  >> >>>> no it is not irrelevant here because if I declare a variable as
>  >> const in
>  >> >>>> my local code the value should not be changed by other code either,
>  >> look at
>  >> >>>> the code in the link given to you earlier which shows just such a
>  >> case as
>  >> >>>> an example on why this is not allowed in C.
>  >> >>>>
>  >> >>>> /HH
>  >> >>>>
>  >> >>>>> Respectfully,
>  >> >>>>> Aleksandr G Povaliaev.
>  >> >>>>>
>  >> >>>>> пн, 24 нояб. 2025 г. в 13:46, Henrik Holst <
>  >> >>>>> [email protected]>:
>  >> >>>>>
>  >> >>>>>> The things is that this is unsafe and invalid due to it creating a
>  >> >>>>>> false sense of security. Aka your "const Foo *" can change under
>  >> your feet
>  >> >>>>>> by _other_ code leading to your const here giving you a false
>  >> sense of
>  >> >>>>>> security. Yes it prevents you from modifying it locally but not
>  >> some other
>  >> >>>>>> code or thread from modifying your const pointer to now point to
>  >> something
>  >> >>>>>> else, hence the compiler issues an error here since you do not get
>  >> what you
>  >> >>>>>> think you are getting.
>  >> >>>>>>
>  >> >>>>>> /HH
>  >> >>>>>>
>  >> >>>>>> Den mån 24 nov. 2025 kl 11:10 skrev Александр Поваляев via
>  >> Gcc-help <
>  >> >>>>>> [email protected]>:
>  >> >>>>>>
>  >> >>>>>>> Hi there!
>  >> >>>>>>>
>  >> >>>>>>> The code is not invalid and neither of the links posted saying
>  >> that
>  >> >>>>>>> "const
>  >> >>>>>>> Foo * const * const" is invalid construction for C.
>  >> >>>>>>> The links posted just are discussing that it might be UNSAFE to
>  >> cast
>  >> >>>>>>> "Foo
>  >> >>>>>>> **" -> "const Foo **" and recommending usage of "Foo **" -> "const
>  >> >>>>>>> Foo *
>  >> >>>>>>> const *" instead.
>  >> >>>>>>> It's OK. If you feel that it is unsafe, please don't use it. It is
>  >> >>>>>>> your own
>  >> >>>>>>> decision.
>  >> >>>>>>>
>  >> >>>>>>> But the syntax itself "const Foo * const * const" is correct and
>  >> the
>  >> >>>>>>> use-case I mentioned is quite simple and evident.
>  >> >>>>>>> And so I need this code snipped to be compiled transparently over
>  >> all
>  >> >>>>>>> the
>  >> >>>>>>> GCC (and platform SDKs) available versions.
>  >> >>>>>>>
>  >> >>>>>>> Respectfully,
>  >> >>>>>>> Aleksandr G Povaliaev.
>  >> >>>>>>>
>  >> >>>>>>>
>  >> >>>>>>> пн, 24 нояб. 2025 г. в 01:48, David Brown <
>  >> [email protected]>:
>  >> >>>>>>>
>  >> >>>>>>>> On 23/11/2025 21:45, Александр Поваляев via Gcc-help wrote:
>  >> >>>>>>>>> Hi there!
>  >> >>>>>>>>>
>  >> >>>>>>>> This is getting /extremely/ frustrating.  /Please/ find some way
>  >> to
>  >> >>>>>>>> learn the C programming language - courses, books, good online
>  >> >>>>>>> resources.
>  >> >>>>>>>> And /please/ believe me when I say that people who have worked
>  >> with
>  >> >>>>>>> C
>  >> >>>>>>>> and C++ for decades, studied the standards, who serve on the
>  >> >>>>>>> standards
>  >> >>>>>>>> committee, know better about these things than you do.  (I'm
>  >> talking
>  >> >>>>>>>> about Jonathan here, not myself - he really is a world-class
>  >> expert
>  >> >>>>>>> here.)
>  >> >>>>>>>>> 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.
>  >> >>>>>>>>>
>  >> >>>>>>>> The links are highly relevant.  They explain why you cannot
>  >> convert
>  >> >>>>>>> from
>  >> >>>>>>>> "char **" to "const char **".  That also explains why you cannot
>  >> >>>>>>> convert
>  >> >>>>>>>> from "char **" to "const char * const * const".  Adding even more
>  >> >>>>>>>> "const" qualifiers to the invalid conversion does not somehow
>  >> >>>>>>> magically
>  >> >>>>>>>> make it work.
>  >> >>>>>>>>
>  >> >>>>>>>>> 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.
>  >> >>>>>>>>>
>  >> >>>>>>>> The compiler is generating an error message because you wrote
>  >> >>>>>>> invalid
>  >> >>>>>>>> code.  The error - or bug, if you like - is in /your/ code.  Not
>  >> the
>  >> >>>>>>>> compiler.  GCC is doing its job correctly here.
>  >> >>>>>>>>
>  >> >>>>>>>>> Respectfully,
>  >> >>>>>>>>> Aleksandr G Povaliaev.
>  >> >>>>>>>>>
>  >> >>>>>>>> I'm sorry, but signing the post with "respectfully" does not
>  >> make it
>  >> >>>>>>>> respectful.  You started the thread disrespectfully - insisting
>  >> that
>  >> >>>>>>>> there is a bug in GCC when you simply do not understand the
>  >> relevant
>  >> >>>>>>>> aspects of the C programming language.  And you have gone
>  >> downhill
>  >> >>>>>>> since
>  >> >>>>>>>> then, ignoring and rejecting the help and advice you have been
>  >> >>>>>>> given.
>  >> >>>>>>>> Getting things wrong once is entirely understandable - this is a
>  >> >>>>>>> subtle
>  >> >>>>>>>> point of the C language, and you are posting to a "help" list.
>  >> >>>>>>> Doubling
>  >> >>>>>>>> down on your ignorance when you have received the help and
>  >> >>>>>>> information
>  >> >>>>>>>> you need, is a different matter entirely.
>  >> >>>>>>>>
>  >> >>>>>>>> Your code is flawed.  You need to fix it.  Mindlessly repeating
>  >> your
>  >> >>>>>>>> misunderstandings about how you think C works will not do
>  >> anything
>  >> >>>>>>> but
>  >> >>>>>>>> annoy people.
>  >> >>>>>>>>
>  >> >>>>>>>> David
>  >> >>>>>>>>
>  >> >>>>>>>>
>  >>
>  >
>