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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: So You Think You Can Const?
Date: Thu, 09 Jan 2025 17:48:08 -0800
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Kaz Kylheku <643-408-1753@kylheku.com> writes:

> On 2025-01-09, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>
>> Julio Di Egidio <julio@diegidio.name> writes:
>>
>>> On 08/01/2025 17:48, Andrey Tarasevich wrote:
>>
>> [...]
>>
>>>> It is perfectly safe.  One can even argue that standard declaration
>>>> if `free` as `void free(void *)` is defective.  It should have been
>>>> `void free(const void *)` from the very beginning.
>>>
>>> I do not understand that:  `free` is changing the pointed data, so
>>> how can `const void *` even be "correct"?
>>
>> No, `free` doesn't (necessarily) change the pointed-to data.
>> Any attempt to access the allocated data after free() has undefined
>> behavior, so it might be modified, but all free() needs to do is
>> make it available for further allocation.  It might do so without
>> touching the data itself.
>
> It doesn't matter because if free were to change the pointed-to
> data, that would be only wrong if the effective type were const.
> [...]

Effective type is irrelevant.  This particular undefined behavior
occurs only when an object _defined_ with a const-qualified type
is changed.  There are no objects defined in a block of memory
allocated by malloc().