CODEWITHSUNDEEP
perlhashcodeperl-data-structures
OpenSourceEnthusiast
OpenSourceEnthusiast

Reputation: 101

Initialize hash elements to 0

I declare a hash in Perl by doing this:

my %hash = ();

I go on adding elements to the hashes. Sometimes, $hash{$x} is not defined, meaning it probably is null. So when I try to print it, I do not get anything. I expect to see a 0 in case that entry $x is not defined. Can someone tell me how do I do this? How do I initialize hash elements to 0 initially?

Upvotes: 2

Views: 1872

Answers (4)

Glitch
Glitch

Reputation: 1

It is possible to initialise the hash.

my %hash = ();
@hash{@keys} = (0) x @keys;

This will create a hash, give it an element for each key and then set the values to an array of 0's as long as the key array.

Upvotes: 0

SamIam
SamIam

Reputation: 1

Note that one doesn't test if a key is defined, but if a key exists using the exists key word. One tests to see if the value is defined with the defined keyword.

print "Exists\n"    if exists $hash{$key};
print "Defined\n"   if defined $hash{$key};
print "True\n"      if $hash{$key};

The first tests if the key exists, the 2nd if the value is defined and the 3rd if the value returns a true value.

Upvotes: 0

Xtof
Xtof

Reputation: 222

There is no such of thing as default value for non defined hash key

the correct way to manipulate hash is to test if your key is defined, with 'defined' function (see perl defined)

[~]=> perl -e '%x = (a=>1, c=>5); for (a..d) { print "$_ => "  . (defined $x{$_} ? $x{$_} :0) . "\n"  }'
a => 1
b => 0
c => 5
d => 0

Upvotes: 0

Benjamin W.
Benjamin W.

Reputation: 52506

Instead of trying to set a default value, you can print a default value when you encounter an undefined value by using the defined-or operator, // (works for Perl 5.10 and higher).

In this example, when you print your hash elements, you either print the element, or if it is not defined, 0:

use 5.010;

say $hash{$x} // 0;

Upvotes: 6

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