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Re: Incompatible pointer types with GCC

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martin.uecker@med.uni-goettingen.de writes:

> On Friday, December 16, 2016 at 11:02:46 PM UTC+1, August Karlstrom wrote:
>> On 2016-12-16 18:07, Ben Bacarisse wrote:
>> > August Karlstrom <fusionfile@gmail.com> writes:
>> > The [] might confuse some people.  This is simply
>> >
>> >         void P(const Row *A)
>> 
>> I prefer to use brackets when a sequence is expected, it provides more 
>> semantic information.
>> 
>> >> test.c:3:6: note: expected ‘const int (*)[10]’ but argument is of type
>> >> ‘int (*)[10]’
>> >>  void P(const Row A[])
>> >>       ^
>> >
>> > I think gcc is right to complain.
>> >
>> > Whilst the types are not compatible, that's not really the problem here.
>> > For example, you can pass an int * to a function that takes const int *
>> > and those two types are not compatible.  Argument passing is done "as if
>> > by assignment", and in an assignment the pointed-to type on the left can
>> > have extra qualifiers.  But here, the const qualifies the element type,
>> > not the pointed-to type, which is an array type.  (C has not qualified
>> > array types at all).
>> 
>> That's counter-intuitive. I thought const applied to Row.
>
> Yes, I hope (and it seems) that this gets fixed in the next revision
> of the C standard. Arrays should behave like structs with respect
> to const but currently they don't. 
>
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1923.htm

Interesting.  Thanks for posting that.

> Without '-pedantic' gcc will accept this, so I recommend to use
> this non-standard extension instead of adding casts which
> break type safety.

Casts can break type safety, but in this case that cast is really just
permitting a safe operation currently ruled out by the language.  It may
be that the value of -pedantic outweighs the concerns about adding what
is, after all, a safe cast.

-- 
Ben.

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Incompatible pointer types with GCC August Karlstrom <fusionfile@gmail.com> - 2016-12-16 11:41 +0100
  Re: Incompatible pointer types with GCC BartC <bc@freeuk.com> - 2016-12-16 11:06 +0000
  Re: Incompatible pointer types with GCC Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-16 17:07 +0000
    Re: Incompatible pointer types with GCC August Karlstrom <fusionfile@gmail.com> - 2016-12-16 23:02 +0100
      Re: Incompatible pointer types with GCC Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-17 00:48 +0000
      Re: Incompatible pointer types with GCC martin.uecker@med.uni-goettingen.de - 2016-12-18 08:06 -0800
        Re: Incompatible pointer types with GCC Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-18 20:11 +0000
          Re: Incompatible pointer types with GCC supercat@casperkitty.com - 2016-12-18 14:43 -0800
            Re: Incompatible pointer types with GCC Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-29 13:33 -0800

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