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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: integer divided by zero
Date: Fri, 25 Apr 2025 13:31:25 -0700
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Thiago Adams <thiago.adams@gmail.com> writes:
> Em 4/25/2025 4:05 PM, Keith Thompson escreveu:
>> Thiago Adams <thiago.adams@gmail.com> writes:
>>> Does anyone know of any platform where integer division by zero
>>> returns a number, or in other words, where it's not treated as an
>>> error? I'm asking because division by zero is undefined behaviour, but
>>> I think division by a constant zero should be a constraint instead.
>> Division by a constant zero is a constraint violation in a context
>> that requires a constant expression.
>
> Consider this sample
>
> int main(){
>     int a[1/0];
> }
>
> 1/0 does not have a value in compile time,
> So I believe compilers are making "a" a VLA because 1/0 is
> not constant.

1/0 is not a constant expression.

A conforming compiler that supports VLAs (C99, or optionally C11 or
later) would make `a` a VLA, with undefined behavior at runtime when
1/0 is evaluated.  For a conforming compiler that doesn't support
VLAs (C89/C90, or optionally C11 or later) the declaration is a
constraint violation.

> (But what old c89 compilers where doing in this case?)
>
> This sample is a motivation to make integer divided by
> zero a constrain.

I consider it motivation not to write code like that.

Sure, I wouldn't mind if using / or % with a right operand
that's a constant expression with value zero (either integer or
floating-point) were a constraint violation, but some compilers
are going to warn about it anyway, and I doubt that such a language
change would catch many errors.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */