Re: Function pointers conversions and UB

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: Function pointers conversions and UB
Date	2017-01-12 13:45 +0000
Organization	A noiseless patient Spider
Message-ID	<87pojsqtmx.fsf@bsb.me.uk> (permalink)
References	<o564ak$fjf$1@dont-email.me> <o57rhu$ioj$1@dont-email.me>

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Noob <root@127.0.0.1> writes:

> On 11/01/2017 21:26, Noob wrote:
<snip>
> Are "void (*)(void *)" and "void (*)(struct s *)" compatible types?
>
> It boils down to the function parameter:
>
> Are "void *" and "struct s *" compatible types?
>
> I think: "no", but I can't find definitive C&V... unless this?

Definitely no.  Type compatibility is very strict: char is not even
compatible with one of signed char and unsigned char.

> 6.2.7 p1 Compatible type and composite type

> "Two types have compatible type if their types are the
> same. Additional rules for determining whether two types are
> compatible are described in 6.7.2 for type specifiers, in 6.7.3 for
> type qualifiers, and in 6.7.5 for declarators."
>
> A type has a type? /me brain exploded

I think that's a typo that comes from incomplete editing.  Maybe it once
said something like "[t]wo values have compatible type if their types
are the same" and someone decided to focus on the types (since types
exists independently of values or objects) and failed to change "their"
to "the".

tl;dr: type compatibility is exact type equality with a few tweaks.

-- 
Ben.

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Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-11 21:26 +0100
  Re: Function pointers conversions and UB "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 15:57 -0500
    Re: Function pointers conversions and UB supercat@casperkitty.com - 2017-01-11 14:37 -0800
  Re: Function pointers conversions and UB jt@toerring.de (Jens Thoms Toerring) - 2017-01-11 21:46 +0000
  Re: Function pointers conversions and UB Keith Thompson <kst-u@mib.org> - 2017-01-11 13:51 -0800
    Re: Function pointers conversions and UB "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 17:06 -0500
  Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 00:29 +0100
    Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-11 23:37 +0000
      Re: Function pointers conversions and UB supercat@casperkitty.com - 2017-01-11 21:49 -0800
        Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 09:41 +0000
      Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 10:52 +0100
        Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 09:58 +0000
  Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 13:08 +0100
    Re: Function pointers conversions and UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-12 13:45 +0000

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