Do not add to hash if it does not exist

[Zhris]

Hey,

I run the following code:

#! /usr/bin/perl
use strict;
use Data::Dumper;

my %products;
my $category = 'Category';
my $product = 'Product';
my $colour = 'Colour';

print Dumper(\%products);
my $productsquantity = (exists $products{$category}{$product}{$colour}) ? $products{$category}{$product}{$colour}{'Quantity'} : '';
print Dumper(\%products);

The first hash dump obviously shows that there is nothing in %products.

The second hash dump shows that $VAR1 = { 'Category' => { 'Product' => {} } } has now been pushed into %products.

However I don't want to push anything into the hash if it doesn't exist. Thats why I have tried to use an exists condition.

How can I ensure that the hash remains empty after attempting to pass a quantity into $productsquantity?

Thanks alot,

Chris

 

[rharsh]

That behavior is called autovivification. There's no easy way to disable it that I know of.

With the example you posted, using exists may give you some unwanted results, you might consider using defined instead.

 

[Zhris]

Thank you,

I have heard of autovivification before but never read up on it. I understand whats happening now.

Your right about using defined instead, within the example. This was what I began with:

my $productsquantity = $products{$category}{$product}{$colour}{'Quantity'};

I think I will simply check if 'Quantity' is defined whilst printing so that any problematic data isn't displayed.

Chris

 

[prex1]

Not sure to understand what you want to do.
If you don't want to create an entry for [tt]'Quantity'[/tt], whatever the value, if any of the upper keys doesn't exist, you possibly want this:

if(exists$products{$category} && exists$products{$category}{$product} && exists$products{$category}{$product}{$colour} && exists$products{$category}{$product}{$colour}{'Quantity'}){
  $productsquantity = $products{$category}{$product}{$colour}{'Quantity'};
}

This construct won't produce autovivification.

Franco

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[Zhris]

Thanks prex1,

Your code works great.

The example I posted is an isolated section from a larger program, having no relevence on its own.

Chris