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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: question about linker
Date: Thu, 28 Nov 2024 01:25:48 -0800
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Thiago Adams <thiago.adams@gmail.com> writes:
> On 27/11/2024 07:29, Waldek Hebisch wrote:
[...]
>> 1) campilers for embedded targets care very much about const.  const
>>     qualified arrays go into read-only data section which is typically
>>     located in flash.  Other arrays go to RAM.  Embedded targets
>>     frequently have very small RAM and larger flash, so after
>>     dropping const program may no longer fit in available RAM.
>
> I think your comment applies for const in declarations like
>
> const int i = 1;
>
> I used to find const confusing, as it sometimes meant 'read-only' and
> other times 'immutable.'

I'm not sure what you mean.  My understanding is that const means
read-only, and nothing else.

> Now, it seems less confusing to me. When const is used with variables
> that can be initialized (init-declarator), it acts as 'immutable',
> meaning the storage is constant.

What exactly do you mean by "the storage is constant"?  Are you talking
about memory that is marked as read-only by the OS?

Given something like:

    const int r = rand();

at block scope, the object will almost certainly be stored in ordinary
read/write memory.  The compiler will flag code that attempts to modify
it (unless you play tricks with pointer casts, which can introduce
undefined behavior).  But if I do something like `*(int*)&r = 42;`,
it's likely to "work".

Defining an object as const can *enable* a compiler to store it in
read-only memory (enforced by the OS, or maybe even physical RAM on some
systems), but that's an implementation choice, not part of the semantics
of const.

[...]

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */