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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Loops (was Re: do { quit; } else { })
Date: Tue, 13 May 2025 15:10:56 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>
>> On 12.05.2025 17:08, David Brown wrote:
>>
>>> On 11/05/2025 23:43, James Kuyper wrote:
>>
>> [...]
>>
>>>> More precisely, it makes it undefined behavior for values to point to an
>>>> array of less than 10 doubles.
>>>
>>> The wording of the C standard (C11, as that's what I have open at the
>>> moment) is :
>>>
>>> """
>>> If the keyword static also appears within the [ and ] of the array type
>>> derivation, then for each call to the function, the value of the
>>> corresponding actual argument shall provide access to the first element
>>> of an array with at least as many elements as specified by the size
>>> expression.
>>> """
>>
>> Oh! - This is somewhat surprising to me. - When I first read about
>> the "arr[static N]" I assumed that it would be possible to pass any
>> sub-array, say "&arr[8]" (or "arr+8") as long as it's large enough
>> to still have N elements from the starting point, but the quote says
>> explicitly "access to the _first_ element of an array" (which I'd
>> interpret as "&arr[0]" (or "arr"). - Unless I misinterpreted that;
>> what would be the reason for that?
>
> My personal interpretation is that this:
>
> void func(int arr[static 5]) {
> }
>
> int main(void) {
>     int arr[10];
>     func(arr+5);    // OK
>     // func(arr+6); // UB
> }
>
> is valid, because, for example, the last 5 elements of a 10-element
> array object can be treated as a 5-element array object.  gcc seems
> to agree, based on the fact that it warns about func(arr+6) but
> not about func(arr+5).
>
> This is a fundamental part of my mental model of C, but in a few
> minutes of searching I wasn't able to find explicit wording in the
> standard that supports it.

In N1570, 6.7.6.3 p7.