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From: Julio Di Egidio <julio@diegidio.name>
Newsgroups: comp.lang.c
Subject: So You Think You Can Const?
Date: Tue, 7 Jan 2025 20:32:50 +0100
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Hi everybody,

I am back to programming in C after many years:
indeed I have forgotten so many things, including
how much I love this language. :)

In particular, I am using C90, and compiling with
`gcc ... -ansi -pedantic -Wall -Wextra` (as I have
the requirement to ideally support any device).

To the question, I was reading this, but I am not
sure what the quoted passage means:

Matt Stancliff, "So You Think You Can Const?",
<https://matt.sh/sytycc>
<< Your compiler, at its discretion, may also choose
    to place any const declarations in read-only storage,
    so if you attempt to hack around the const blocks,
    you could get undefined behavior. >>

I do not understand if just declaring that a pointer
is to constant data may incur in that problem even
if the pointed data was in fact allocated with malloc.
I would say of course not, but I am not sure.

E.g. consider this little internal helper of mine
(which implements an interface that is public to
do an internal thing...), where I am casting to
pointer to non-constant data in order to free the
pointed data (i.e. without warning):

```c
static int MyStruct_free_(MyStruct_t const *pT) {
     assert(pT);

     free((MyStruct_t *)pT);

     return 0;
}
```

Assuming, as said, that the data was originally
allocated with malloc, is that code safe or
something can go wrong even in that case?

Thank in advance for any help/insight,

Julio