error but code works

[Gary Stainburn]

Hi folks,

I've got the following code which works, but generates the error message
following it. I've tried varying the code to eliminate the error but I only
manage to get either the working code with error or non-working code without
error.

(Line 95 is the while line)

print "checking file $fname...";
open DAT,"<$fname" ||die "cannot open $fname: $!\n";
my $found=0;
while ((my $line=<DAT>) && (! $found)) {
print "line=$line" if ($DEBUG > 0);
$found=1 if $line=~/$localpart:/;
}
close DAT;

root@stan input]# tidy-mailq|gvim -
Value of <HANDLE> construct can be "0"; test with defined() at
/root/bin/tidy-mailq line 95.
Vim: Reading from stdin...
[root@stan input]#
--
Gary Stainburn

This email does not contain private or confidential material as it
may be snooped on by interested government parties for unknown
and undisclosed purposes - Regulation of Investigatory Powers Act, 2000

[Bob Showalter]

Gary Stainburn wrote:

> Hi folks,
>
> I've got the following code which works, but generates the error
> message following it. I've tried varying the code to eliminate the
> error but I only manage to get either the working code with error or
> non-working code without error.
>
> (Line 95 is the while line)
>
> print "checking file $fname...";
> open DAT,"<$fname" ||die "cannot open $fname: $!\n";
> my $found=0;
> while ((my $line=<DAT>) && (! $found)) {
> print "line=$line" if ($DEBUG > 0);
> $found=1 if $line=~/$localpart:/;
> }
> close DAT;
>
> root@stan input]# tidy-mailq|gvim -
> Value of <HANDLE> construct can be "0"; test with defined() at
> /root/bin/tidy-mailq line 95.
> Vim: Reading from stdin...
> [root@stan input]#

From perldoc perldiag:

Value of %s can be ""0""; test with defined()
(W misc) In a conditional expression, you used <HANDLE>, <*>
(glob), "each()", or "readdir()" as a boolean value. Each of these
constructs can return a value of "0"; that would make the condi-
tional expression false, which is probably not what you intended.
When using these constructs in conditional expressions, test their
values with the "defined" operator.

changing:
while ((my $line=<DAT>) && (! $found)) {

to
while (defined(my $line=<DAT>) && (! $found)) {

should make the warning go away.

[James Edward Gray II]

On Jan 29, 2004, at 8:07 AM, Gary Stainburn wrote:

> Hi folks,
>
> I've got the following code which works, but generates the error
> message
> following it. I've tried varying the code to eliminate the error but
> I only
> manage to get either the working code with error or non-working code
> without
> error.
>
> (Line 95 is the while line)
>
> print "checking file $fname...";
> open DAT,"<$fname" ||die "cannot open $fname: $!\n";
> my $found=0;
> while ((my $line=<DAT>) && (! $found)) {
> print "line=$line" if ($DEBUG > 0);
> $found=1 if $line=~/$localpart:/;
> }
>

How about we simplify that loop a little:

while (<DAT>) {
print "line=$_" if $DEBUG;
last if /$localpart/;
}

That's a little easier on the eyes, I think. It means the same and it
will remove the error.

Hope that helps.

James

> close DAT;
>
> root@stan input]# tidy-mailq|gvim -
> Value of <HANDLE> construct can be "0"; test with defined() at
> /root/bin/tidy-mailq line 95.
> Vim: Reading from stdin...
> [root@stan input]#
> --
> Gary Stainburn
>
> This email does not contain private or confidential material as it
> may be snooped on by interested government parties for unknown
> and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
>
>
> --
> To unsubscribe, e-mail: [email]beginners-unsubscribe@perl.org[/email]
> For additional commands, e-mail: [email]beginners-help@perl.org[/email]
> <http://learn.perl.org/> <http://learn.perl.org/first-response>
>
>
>

[Jeff 'Japhy' Pinyan]

On Jan 29, Gary Stainburn said:

>I've got the following code which works, but generates the error message
>following it. I've tried varying the code to eliminate the error but I only
>manage to get either the working code with error or non-working code without
>error.

It's not an error message, it's a warning. And it tells you what to do.

> open DAT,"<$fname" ||die "cannot open $fname: $!\n";
> my $found=0;
> while ((my $line=<DAT>) && (! $found)) {
> print "line=$line" if ($DEBUG > 0);
> $found=1 if $line=~/$localpart:/;
> }
> close DAT;

>Value of <HANDLE> construct can be "0"; test with defined() at

If you turn on 'use diagnostics', it will explain more about this warning.
Suffice to say, reading from a filehandle can return JUST the string '0',
which is technically false, and this will stop your while loop. If you
don't want that to happen, you wrap the assignment in defined():

while (defined(my $line = <DAT>) and not $found) { ... }

But I'd suggest rewriting your code thus:

while (<DAT>) {
print "line=$_" if $DEBUG > 0;
$found = 1, last if /$localpart:/;
}

Here, we exit the loop immediately when $found is set. This lets us use a
simply while clause (<DAT>) which assigns to $_ and tests for defined-ness
implicitly.

--
Jeff "japhy" Pinyan [email]japhy@pobox.com[/email] [url]http://www.pobox.com/~japhy/[/url]
RPI Acacia brother #734 [url]http://www.perlmonks.org/[/url] [url]http://www.cpan.org/[/url]
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]

[Gary Stainburn]

On Thursday 29 Jan 2004 2:25 pm, James Edward Gray II wrote:

> On Jan 29, 2004, at 8:07 AM, Gary Stainburn wrote:

> > Hi folks,
> >
> > I've got the following code which works, but generates the error
> > message
> > following it. I've tried varying the code to eliminate the error but
> > I only
> > manage to get either the working code with error or non-working code
> > without
> > error.
> >
> > (Line 95 is the while line)
> >
> > print "checking file $fname...";
> > open DAT,"<$fname" ||die "cannot open $fname: $!\n";
> > my $found=0;
> > while ((my $line=<DAT>) && (! $found)) {
> > print "line=$line" if ($DEBUG > 0);
> > $found=1 if $line=~/$localpart:/;
> > }

>
> How about we simplify that loop a little:
>
> while (<DAT>) {
> print "line=$_" if $DEBUG;
> last if /$localpart/;
> }

Hi James,

my problem was having the result in $found after the loop ended, I've amended
your code so that I have

if (/$localpart:/) { $found=1; last;}

Thanks for the help.

Gary

>
> That's a little easier on the eyes, I think. It means the same and it
> will remove the error.
>
> Hope that helps.
>
> James
>

> > close DAT;
> >
> > root@stan input]# tidy-mailq|gvim -
> > Value of <HANDLE> construct can be "0"; test with defined() at
> > /root/bin/tidy-mailq line 95.
> > Vim: Reading from stdin...
> > [root@stan input]#
> > --
> > Gary Stainburn
> >
> > This email does not contain private or confidential material as it
> > may be snooped on by interested government parties for unknown
> > and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
> >
> >
> > --
> > To unsubscribe, e-mail: [email]beginners-unsubscribe@perl.org[/email]
> > For additional commands, e-mail: [email]beginners-help@perl.org[/email]
> > <http://learn.perl.org/> <http://learn.perl.org/first-response>

--
Gary Stainburn

This email does not contain private or confidential material as it
may be snooped on by interested government parties for unknown
and undisclosed purposes - Regulation of Investigatory Powers Act, 2000