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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: "Conversions" of types
Date: Mon, 10 Jun 2019 14:00:02 -0700
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unidef <jon@unidef-systems.com> writes:
> Keith Thompson <kst-u@mib.org> wrote:
>> ram@zedat.fu-berlin.de (Stefan Ram) writes:
>>> |Any pointer type may be converted to an integer type.
>>> N2310, 6.3.2.3p6
>>> 
>>> If this is true, then may I ask: Which integer type
>>> is the result of the conversion of the pointer type
>>> »double *« to an integer type?
>>> 
>>> Don't they mean:
>>> 
>>> Any /value of/ an expression of pointer type may be 
>>> converted to a /value of/ an integer type.
>> 
>> Yes.
>> 
>>> ? Or does it really make sense to say that a /type/
>>> can be converted to another type?
>> 
>> No.  The wording in the standard is slightly informal.  The intent is
>> clear enough that I don't have a problem with it, though I wouldn't
>> mind if it were changed to refer to values.
>> 
>
> You gotta look into the machines native assembly code to make sense out of
> casting. I don’t know assembly that well :(

No, you don't have to look at assembly code to make sense out
of casting.  The semantics of casts, and more generally of
type conversions, are defined by the standard (and are left
implementation-defined in some cases).

For pointer conversions (pointer-to-pointer, pointer-to-integer, or
integer-to-pointer), it helps to know how pointers are represented,
but knowing about the CPU instructions instructions that act on them
is not particularly helpful.  On most systems, pointer conversions
just copy the bits; the only slightly tricky part is making sure
that the source and target have consistent sizes.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */