error when passing hash as reference causes

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

I tried my best to read copious threads on this site regarding the subject of passing hashes. To say the least, this subject has been hashed and rehashed (sorry).

I cannot seem to correctly pass hashes as references. I will need to do this in order to pass more than one hash or a hash along with other parms.

I keep getting errors along the likes of:

Not a CODE reference at ./hashTest.pl line 33.

or:

Can't use string ("me") as a HASH ref while "strict refs" in use ...

The code resembles most of the reference examples on this site. I get the errors on Linux and IRIX.

#!/usr/bin/perl -w

use strict;

my %hash = (
   's'   => '1',
   'e'   => '200',
   'b'   => '1', 
   'me'  => '0',
   'mf'  => '0',
   'im'  => '/usr/tmp/cache/ccarden/earth/images/earth',
   'pad' => '4',
   'yh'  => '191',
   'yl'  => '0',
   'of'  => 'jpg',
   'x'   => '1024',
   'y'   => '768'
);

sub print_h {
    my %new_hash = @_;

    foreach (keys %new_hash) {
        print "  Key: $_,\t Value: $new_hash{$_}\n";
    }
}

sub print_h_byref {
    my $href = shift;
    my ($value, $key);

    foreach $key (keys %$href) {
        $value = $href->($key);
        print "  Key: $key,\t Value: $value\n";
    }
}

print_h (%hash);
print "\n";
print_h_byref (\%hash);
[download]

I don't know if anyone else will get the errors. Judging by the examples I've seen, I think not. But any elucidation and correction would be much appreciated. Thanks.

Comment on error when passing hash as reference causes Download Code

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Re: error when passing hash as reference causes by dmitri (Priest) on Sep 11, 2003 at 21:33 UTC
This code: `$value = $href->($key);` [download] should use curly braces (indicating that `$hash` is a reference to a hash), not parentheses (indicating that `$hash` is a reference to a function). The line in question tries to call a subroutine referenced by `$hash`, hence the error message.	[reply] [d/l]
Re: error when passing hash as reference causes by NetWallah (Canon) on Sep 11, 2003 at 23:54 UTC
You can also make your print_h_byref code a little easier to read by using the example from the documentation of the "each" function: `sub print_h_byref { my $href = shift; while (my ($key, $value) = each %$href) { print " Key: $key,\t Value: $value\n"; } }` [download] Your print_h function makes a local copy of the hash. You should be aware that this may become an issue for large hashes, or if it is called a large number of times.	[reply] [d/l]
Re: error when passing hash as reference causes by jdtoronto (Prior) on Sep 12, 2003 at 03:09 UTC
This will work: #!/usr/bin/perl -w use strict; my %hash = ( 's' => '1', 'e' => '200', 'b' => '1', 'me' => '0', 'mf' => '0', 'im' => '/usr/tmp/cache/ccarden/earth/images/earth', 'pad' => '4', 'yh' => '191', 'yl' => '0', 'of' => 'jpg', 'x' => '1024', 'y' => '768' ); sub print_h { my %new_hash = @_; foreach (keys %new_hash) { print " Key: $_,\t Value: $new_hash{$_}\n"; } } sub print_h_byref { my $href = shift; while (my ($key, $value) = each %$href) { print " Key: $key,\t Value: $value\n"; } } print_h (%hash); print "\n"; print_h_byref (\%hash); [download] Which is, I think, close to what somebody else suggested. You can tidy up that sub and also avoid the error you made :) jdtoronto	[reply] [d/l]