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Defined and Exists, but what about neither?

by c (Hermit)
on Aug 21, 2002 at 13:27 UTC ( #191725=perlquestion: print w/replies, xml ) Need Help??

c has asked for the wisdom of the Perl Monks concerning the following question:

I have a subroutine that a hash reference passed to it...

&log_action(\%args);

In my mains code, I test for an error and then stuff the value into $args{err} (This is being done through a Net::SNMP function)

$args{err} = $s->error();

Now, within the log_action subroutine, I pull in my hash reference

sub log_action { my $args = shift;

And I test to see if there is was an error message

if ($args->{err}) { # do something...

Is this a suitable method? I read through defined and exists and it seems as though

if (defined $args->{err}) {

may be more appropriate. How does perl judge if (args->{err}) when neither is used?

And as a follow up question regarding whether defined or exists is the better to use... If there is no error returned via the Net::SNMP call, according to its documentation, it "returns an empty string". Please correct me if I am wrong, but this means that there will be a hash key present called $args{err} but there will be no value associated with it?

Thanks -c

Replies are listed 'Best First'.
Re: Defined and Exists, but what about neither?
by Abigail-II (Bishop) on Aug 21, 2002 at 13:42 UTC
    No, that is not possible. If there is a key present there is also a value. The value could be undefined though.
    exists $hash {key} && print "Key is present, value may be undefined." +; defined $hash {key} && print "Key is present, and its value is defined +."; $hash {key} && print "Key is present, its value is defined and + true.";
    Of course, this is also documented in the manual: perldoc -f exists.

    Abigail

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