Re: "Arithmetic exception" with modulus operator '%'

[Szabolcs Nagy <nsz@port70.net>]

* jounijl@yahoo.co.uk <jounijl@yahoo.co.uk> [2019-02-15 03:35:23 +0000]:
> As in the headline. Program stops and prints "Arithmetic exception" at the
> line where the modulus operator '%' is.
> 
> I'm compiling in Alpine linux with clang installed from apk:s:
> 
> clang -c test.c
> clang -o test test.o
> 
> The code is:
> 
> ----- snip -----
>         unsigned int unum  = 0;
>         unsigned int umod  = 0;
>         unsigned int ures  = 0;
>         ures = unum % umod; // <-- this one

undefined behaviour == anything can happen

the compiler can drop this entirely.

> ----- /snip -----
> 
> The variables have some values other than 0.
> 
> The environment is:
> The Alpine Linux is installed in Oracle Virtualbox in FreeBSD 12, 64-bit
> Intel.

x86_64 traps mod by 0 (in case the compiler didn't
drop the code path because of ub).

> 
> $ uname -a
> Linux localhost 4.14.89-0-vanilla #1-Alpine SMP Tue Dec 18 16:10:10 UTC 2018
> x86_64 GNU/Linux
> 
> $ clang --version
> Alpine clang version 5.0.1 (tags/RELEASE_501/final) (based on LLVM 5.0.1)
> 
> What does this? Do I need to include some library?

what behaviour do you expect?

> 
> w.b.reg., Jouni