Re: integer divided by zero

On 25/04/2025 17:31, Keith Thompson wrote:

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.
 

Another interesting example
enum {A = ((-2147483647-1) / -1)};
In this case it is a constant expression.
The resulting value is -2147483648 of type int.
The mathematically correct value is 2147483648 that does not fit
in a integer.