Hash problem: each() failure

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

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Re: Hash problem: each() failure by Corion (Patriarch) on Feb 22, 2008 at 09:43 UTC
The error is at the top of your code: `my %Cls = {'P','a','N','b','U','c'};` You need to assign a list, not a hash reference to your hash: `my %Cls = ('P','a','N','b','U','c');` [download]	[reply] [d/l]
Re: Hash problem: each() failure by hipowls (Curate) on Feb 22, 2008 at 09:55 UTC
And if warnings had been enabled you would have been told about it. `Reference found where even-sized list expected at Perl-1.pl line 7.` [download]	[reply] [d/l]
Re: Hash problem: each() failure by cdarke (Prior) on Feb 22, 2008 at 14:11 UTC
Further to what Corion said, you actually created a hash with a single key. The key was a hash reference and its value undef. The braces `{...}` create an anonymous hash and return a reference to it. You could have done this: `my $Cls = {'P','a','N','b','U','c'}; print %$Cls,": \n\n"; while ( my ($k, $v) = each(%$Cls) ) { print "$k => $v\n"; }` [download] Note in the print statement I changed the '.' to a ','. The dot operator forces the hash into scalar context, which is rairly useful.	[reply] [d/l] [select]
Re: Hash problem: each() failure by peter (Sexton) on Feb 22, 2008 at 13:14 UTC
A stringified hash will show the capacity of the hash. This is (almost) never a useful value. Peter Stuifzand	[reply]
Re: Hash problem: each() failure by DigitalKitty (Parson) on Feb 23, 2008 at 18:12 UTC
Hi Anonymous Monk. As Corion mentioned, you used the anonymous hash syntax, i.e., `$name_of_hash = { ... };` Assigning a list to a hash variable will result in the key/value pair(s) being created. `use warnings; use strict; my %Cls = qw( P a N b U c ); print %Cls, "\n\n"; while ( my ($k, $v) = each( %Cls ) ) { print "$k => $v\n"; }` [download] Update: Fixed typo by changing `%name_of_hash = { ... };` to `$name_of_hash = { ... };` after ikegami++ noticed it. Thanks. Hope this helps, ~Katie	[reply] [d/l] [select]
Re: Hash problem: each() failure by Anonymous Monk on Feb 24, 2008 at 17:05 UTC
To add to the already great comments made... When you initialize a hash it is standard convention to use '=>' between key/value pairs rather than commas... e.g. {'P' =>'a','N' =>'b','U' =>'c'} it is strictly a readability thing, but since code is written for people, readability is everything Since a hash is just a "special" array, it may be easier to understand the problem by looking at an array example. If you initialiaze an array with square brackets you get a reference to the array. On the other hand, if you initialize with parentheses @x = ('P','a','N','b','U','c'); you will get the actual array. Creating the hash with the {} braces works like the square brackets on an array. Another great comment made was to suggest you should enable warnings on your code. I cannot agree more. You should just get in the automatic habit of adding strict and warnings to everything you write. e.g. #!/usr/bin/perl use strict; use warnings; my 2 bits... Anyone know how to get square brackets to show up in my source listing on the perl monks site?	[reply]
Re: Hash problem: each() failure by Anonymous Monk on Feb 24, 2008 at 16:46 UTC
Was ist rather this you wanted? my %Cls = ('P' => 'a', 'N' => 'b', 'U' => 'c'); print %Cls.": \n\n"; foreach $a (keys(%Cls)) { print "$a => $Cls{$a}\n"; }	[reply]
Re: Hash problem: each() failure by Anonymous Monk on Feb 22, 2008 at 22:26 UTC
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