Re: A: a new bug to old plain C

LIU Hao via Gcc-help <[email protected]> Thu, 27 Nov 2025 19:29:37 +0800
Newsgroups	gmane.comp.gcc.help
Message-ID	<[email protected]>
在 2025-11-27 18:28, Александр Поваляев 写道:
> 2) Second, there is no explicit prohibition of such conversion ("Foo**" -> "const Foo*const*const) in C 
> standard.

How hard for you would it be to comprehend that the paragraph which starts with 'one of the following 
shall hold' has a bold word 'Constraints' in front of it so your code is identified as a constraint 
violation and is such undefined behavior?

Oh maybe you are not willing to read the standard so I quote it for you:

    5.1.1.3 Diagnostics
    1 A conforming implementation shall produce at least one diagnostic message
      (identified in an implementation-defined manner) if a preprocessing
      translation unit or translation unit contains >>>>>>> a violation of any
      syntax rule or constraint <<<<<<<, even if the behavior is also explicitly
      specified as undefined or implementation-defined. Diagnostic messages need
      not be produced in other circumstances.


> 3) Half of well-known compilers don't treat such conversion ("Foo**" -> "const Foo*const*const) as an 
> error. They might show a warning or doesn't show it.

It's undefined behavior so compilers are free to accept it (with a warning) or reject it (with an error).


> 4) I showed a use-case where such conversion might be useful and why. I think all the participants have 
> read that post.

I understand it's useful. Right. But no matter how weird it looks, it's C. The standard says it's 
undefined behavior, and what you think does not matter, at, all.


> 5) IF WE ARE TALKING ABOUT UNIFYING OF C STANDARD IMPLEMENTATION OVER ALL THE COMPILERS AVAILABLE, WE 
> CAN'T MAKE A PROHIBITION AS A GENERAL RULE, SINCE
>      WE WILL FACE OUT BACK-COMPATIBILITY ISSUE WITH THE COMPILERS WHICH HAVE ALREADY HAD SUPPORT OF SUCH 
> CONVERSION.

So it seems that you are unable to agree with what others agree, you are proactively violating the C 
standard, and you are claiming that your disability is causing *your* issue. Oh, maybe that's just you.



-- 
Best regards,
LIU Hao
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