Re: Question about a programme

On 18 Feb., 15:14, Ed Morton <mor...@[EMAIL PROTECTED]
> wrote:
> On 2/18/2008 6:57 AM, Spiros Bousbouras wrote:
>
> > On page 194 of "Effective AWK programming" we see the
> > following programme:
>
> > # rewind.awk --- rewind the current file and start over
> > function rewind( =A0 =A0i)
> > {
> > =A0 =A0 # ****ft remaining arguments up
> > =A0 =A0 for (i =3D ARGC; i > ARGIND; i--)
> > =A0 =A0 =A0 =A0 ARGV[i] =3D ARGV[i-1]
> > =A0 =A0 # make sure gawk knows to keep going
> > =A0 =A0 ARGC++
> > =A0 =A0 # make current file next to get done
> > =A0 =A0 ARGV[ARGIND+1] =3D FILENAME
> > =A0 =A0 # do it
> > =A0 =A0 nextfile
> > }
>
> > Isn't the statement ARGV[ARGIND+1] =3D FILENAME
> > superfluous ? In the loop when i gets the
> > value ARGIND + 1 then the assignment
> > ARGV[ARGIND + 1] =3D ARGV[ARGIND] will be executed
> > and ARGV[ARGIND] always has the same value as
> > FILENAME
>
> But what if the current file is the last one? Then i =3D ARGC =3D ARGIND
a=
t the
> start of the loop, so the loop's never entered so THEN that final
assignme=
nt is
> required. Although that works in this context since the functiona name
imp=
lies
> it MUST be called while parsing a file, use of FILENAME meanse you can't
e=
xecute
> this type of general "****ft the arguments" function in a BEGIN section
so =
I'm
> not a big fan.

While filename is just unset in the BEGIN block it seems there's a
more fatal problem with 'nextfile' in rewind()...

$ xgawk 'BEGIN{nextfile}'
xgawk: error: `nextfile' used in BEGIN action

Note: I've just xgawk at hand but suppose that error is inherited
from gawk.

Janis

>
> Personally, I expect I'd have written it as:
>
> # rewind.awk --- rewind the current file and start over
> function rewind( =A0 =A0i)
> {
> =A0 =A0 # ****ft remaining arguments up
> =A0 =A0 for (i =3D ++ARGC; i > ARGIND; i--)
> =A0 =A0 =A0 =A0 ARGV[i] =3D ARGV[i-1]
> =A0 =A0 # do it
> =A0 =A0 nextfile
>
> }
>
> (leaving out the "nextfile" for a general "****ft" function) but I
haven't
> thought about it much and maybe there was something else the author was
tr=
ying
> to show with that example...
>
> =A0 =A0 =A0 =A0 Ed.