Re: Unexpected result while constructing strings

[Hermann Peifer]

On 30/10/2010 16:05, Davide Brini wrote:
> On Sat, 30 Oct 2010 16:00:20 +0200 Hermann Peifer<address@hidden>  wrote:
>
> > I think I got it now: `FS ++c' is not (mis)interpreted as `FS + +c', but
> > rather as `FS++ c'. See below. Let's see if Arnold agrees.
> >
> > Hermann
> >
> > $ cat data
> > A
> > B
> > C
> > $ gawk-stable/gawk --dump-variables '{ print FS ++c }' data ; tail -n1
> > awkvars.out
> > 0
> > 1
> > 2
> > c: string ("")
> > $ gawk-stable/gawk --dump-variables '{ print FS++ c }' data ; tail -n1
> > awkvars.out
> > 0
> > 1
> > 2
> > c: string ("")
> Thanks. It seems you're right indeed:
>
> $ gawk 'BEGIN{ c++; print FS ++c ; print FS}'
> 01
> 1
> $ gawk --dump-variables 'BEGIN{ c++; print FS++ c ; print FS}'
> 01
> 1
> $ grep -E '^(c|FS)' awkvars.out
> FS: number (1)
> c: number (1)
>
> That would explain the leading 0 (FS converted to number before the
> postincrement). Still, it seems weird to me that "FS ++c" is parsed
> as being a postincrement for FS, despite the intervening space. A (very)
> quick look at the grammar doesn't seem to allow that.
>
> But yes, it seems that it happily accepts it:
>
> $ gawk 'BEGIN{ print ++   c}'
> 1

Just to add another (somewhat surprising) result:

$ gawk-stable/gawk --dump-variables '{ print -- FS++ c }' data ; egrep 
"^(FS|c)" awkvars.out
-11
-22
-33
FS: number (-3)
c: number (3)

Hermann