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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: =?UTF-8?Q?Re=3A_technology_discussion_=E2=86=92_does_the_world_need?=
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Date: Wed, 10 Jul 2024 00:04:40 +0100
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On 09/07/2024 23:32, Kaz Kylheku wrote:
> On 2024-07-09, bart <bc@freeuk.com> wrote:
>> On 09/07/2024 16:58, Ben Bacarisse wrote:
>>> bart <bc@freeuk.com> writes:
>>>
>>>> Arrays are passed by reference:
>>>>
>>>>     void F(int a[20]) {}
>>>>
>>>>     int main(void) {
>>>>       int x[20];
>>>>       F(x);
>>>>     }
>>>
>>> This is the sort of thing that bad tutors say to students so that they
>>> never learn C properly.  All parameter passing in C is by value.  All of
>>> it.  You just have to know (a) what the syntax means and (b) what values
>>> get passed.
>>
>> The end result is that a parameter declared with value-array syntax is
>> passed using a reference rather than by value.
>>
>> And it does so because the language says, not because the ABI requires
>> it. A 2-byte array is also passed by reference.
> 
> In C, arrays are not passed to functions, period.

Arrays can be passed by explicit reference:

   void F(int(*A)[20]) {
       printf("%zu\n", sizeof(*A)/sizeof((*A)[0]));    // shows 20
   }


That can be called like this:

   int a[20];
   F(&a);


Here, an actual array type is involved, which is passed by an actual 
pointer to array, not a pointer to its elements.

> Therefore ABIs do not say anything about array parameters,
> (or if they do, it's not in relation to C).

That makes a change; most people think that C invented ABIs, which were 
created in its image.

The Win64 ABI talks about aggregate types.