CODEWITHSUNDEEP
perlhashreferenceexists
DarenW
DarenW

Reputation: 16906

Why is testing if a key exists in a hash not working for ref to hash?

How do tell if a key exists in a has, when I have a reference to the hash? The following seemed simple and obvious (at my level of expertise) but prints out something other than expected:

%simple = (a => 8, b=> 9);
print  0+exists $simple{a},  0+exists $simple{c},   "\n";    # prints 10

%href = \%simple;
print  0+exists $href{a},  0+exists $href{c},  "\n";        # expect fail; bad syntax
print  0+exists $href->{a},  0+exists $href->{c},  "\n";    # should work
print  0+exists ${$href}{a},  0+exists ${$href}{c},  "\n";  #  should work
print  0+exists $$href{a},  0+exists $$href{c},  "\n";      # not sure

# see if attempt to ask about {c} accidently created it
print %simple, "\n";

This prints out 

10
00
00
00
00
a8b9

I expect (being very optimistic):

10
10
10
10
10
a8b9

I don't expect all the ways I tried to work but at least one should. I've gone over perldoc, other SO questions, and Googling all over, and all I come up with is that the syntax I use in some of these lines should work.

Upvotes: 0

Views: 826

Answers (1)

geekosaur
geekosaur

Reputation: 61369

The line

%href = \%simple;

doesn't do what you think it does; perl -w (or use warnings;) would give you a warning about an odd number of hash elements, which should be a sufficient hint as to what it tried to do (and, if you think about it, why your "bad syntax" isn't). Try

$href = \%simple;

Also, learn to use use warnings; and use strict;, and always use them.

Upvotes: 2

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