On Thu, Dec 29, 2022 at 06:23:09PM +0100, Steffen Nurpmeso wrote:
> Hello.
>
> Name: bash
> Path: /usr/ports/core
> Version: 5.2.15
> Release: 1
>
> $ i=10 j=20;echo $(( i += j += i += j ));echo $i,$j
> 60
> 60,50
> $ i=10 j=20;echo $(( i += j += i += i ));echo $i,$j
> 50
> 50,40
You are modifying something that is used elsewhere in an expression. I am not
surprised that you do not get what you expect; others might expect something
different.
At most there should be a note in the documentation that this sort of thing
leads to undefined behaviour -- that is what happens in other languages.
This is very much not a bug in bash.
C does it differently. I would not be surprised to see different C compilers
produce different results or different results with different levels of
optimisation.
> $ cat t.c
> #include <stdio.h>
> int main(void){
>
> int i, j;
>
> i = 10, j = 20;
> i += j += i += j;
> printf("%d,%d\n", i, j);
>
> i = 10, j = 20;
> i += j += i += i;
> printf("%d,%d\n", i, j);
>
> return 0;
> }
> $ tcc -run t.c
> 80,50
> 60,40
>
> --steffen
> |
> |Der Kragenbaer, The moon bear,
> |der holt sich munter he cheerfully and one by one
> |einen nach dem anderen runter wa.ks himself off
> |(By Robert Gernhardt)
>
--
Alain Williams
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Lecturer.
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