SPUG: Something to loose sleep over
David Waring
dwaring at nwsr.com
Fri Apr 28 03:19:50 CDT 2000
Warning this is a demonstration of a bug that only appears in certain
installations of Perl. It is a weird bug and I am really pointing it
out as a topic of conversation. Ignore this if you are not interested
in really yucky stuff.
We have recently had a problem with passing parameters to a
subroutine. It only appears on one of our many boxes that are all
running the same version of Perl (can't remember the version but it
is pre 5.6) All boxes are running AIX.
To paraphrase the code as closely as possible
.....
# call a subroutine several times with different parameters
asubroutine(\@A,"B","C");
asubroutine(\@D,"E","F");
asubroutine(\@X,"Y","Z");
sub asubroutine{
print @_,\n";
$x= shift @_;
$y= shift @_;
$z= shift @_;
}
RESULTS
ABC
ABC
ABC
whoa thats weird the subroutine is acting like it was called three
times with the same parameters
Now we can fix this in several ways. All of the following changes
behaved properly an had the expected results of
ABC
DEF
XYZ
1) get rid of the multiple shifts and instead grab all the incoming
params at once as any normal person would do
($x,$y,$z) = @_;
2) forget about $z and only shift in the x y values leaving @_ with a
single value
3) stop passing the reference in the params just pass the 'normal' scalars;
4) removing all the shifts and just printing @_
I mean how on earth can what is done later with @_ affect the values
in it?????????
Doing #1 but then setting @_ = (); -- which should be pretty damn
close to shifting out all the values from @_ worked normally.
The Print statement before the shifts was not important. The wrong
values were being set for x y z anyway.
We will be reinstalling Perl on this box but does anyone have any
idea what in the deepest bowels of Perl could be going on here????
David Waring
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
POST TO: spug-list at pm.org PROBLEMS: owner-spug-list at pm.org
Seattle Perl Users Group (SPUG) Home Page: http://www.halcyon.com/spug/
SUBSCRIBE/UNSUBSCRIBE: Replace "action" below by subscribe or unsubscribe
Email to majordomo at pm.org: "action" spug-list your_address
More information about the spug-list
mailing list