http://www.perlmonks.org?node_id=633373

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

I just got bit by a nasty bug and I'm trying to figure out how this error snuck through my checks. The top-level call: 
my $respCodes = $processor->delayedCapture( 
           CCTYPE => $row->{debitacct},                               
+                          
           ORIGID => $row->{auth_code},
           CURRENCY_TYPE_ID => $row->{currency_type_id} );

croak "Failed authorization for TXID $row->{txid} " 
   unless ( $respCodes->{SUCCESS} == 1 );

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I'm performing an equality test, so I would think that if  $responseCode doesn't equal 1, this routine would  croak

But it gets slightly more complicated. The called routine ( processPayment() ) performs a similar hashref key comparison when building up its return value. 

   return { SUCCESS => $response->{RESULT} == 0,
            MESSAGE => $response->{RESPMSG},
           AUTHCODE => $response->{AUTHCODE},
            PNREF   => $response->{PNREF},
            CC_TYPE => $params{CCTYPE},
      TOTAL_PAYMENT => $params{AMOUNT},
      CHECK_DETAILS => $checkInfo,
            };

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If $response is still a scalar (meaning that nothing happened to it after declaring it in the subroutine), shouldn't the value of $response->{SUCCESS} be  undef (due to autovivification) rather than having  $response->{SUCCESS} == 0 evaluate to true?

I see where the caller ( the first calls listed in this entry ) would make the mistake with the hashkey comparison since the error was introduced in  $processor->delayedCapture(). But how can  $foo->{bar} == 0 evaluate to true?

I don't know if my solution is the best one, but I've added a  defined check in the creation of the return value of  delayedCapture(): 

   return { SUCCESS => ( defined $response->{RESULT} && $response->{RE
+SULT} == 0 ),
 ....

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Replies are listed 'Best First'.
Re: hashref value comparison
by kyle (Abbot) on Aug 17, 2007 at 19:29 UTC

    When undef is treated as a number, it's equal to zero. When it's treated as a string, it's equal to ''. 

    $ perl -le 'print "true" if undef == 0;'
true
$ perl -le 'print "true" if undef eq "";'
true

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    Checking to make sure the value is defined before comparing to zero is the right way to go.

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[d/l]
[select]
      Thanks.

      I don't know why I thought  undef acted more like a NULL value ...

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[d/l]

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