vinoth.ree has asked for the wisdom of the Perl Monks concerning the following question: 

 use strict;
use warnings;
use Data::Dumper;
my $hash_ref={1002=>[1,2,3,4,5],1001=>[6,7,8,9,10],3=>[2]};
my ($key,$val);
foreach(($key,$val)=each %$hash_ref){
    print "Each()=======================>$key=>$val<==================
+=====\n";
    print "Default>>>>>>>>>>>>>>>>$_<<<<<<<<<<<<<<<<<<\n";
}

[download]

I just tried to get the pair of key and value from the hash reference, I got what I want using the while loop, when I go for 'foreach' I count not understand what is happening ? Any idea pl!

Update

Title changed.

Replies are listed 'Best First'.
Re: What is happening ?
by tilly (Archbishop) on Aug 19, 2009 at 05:48 UTC
    You are assigning a single key/value pair to $key and $value, then making a list of 2 elements out of that list, then iterating over that list of 2 elements.

    The next time you call each you'll get the next pair out of the hash.

    The usual way to do what you likely want is: 

    foreach my $key (keys %$hash_ref) {
    my $value = $hash_ref->{$key};
    ...
}

    [download]
[reply]
[d/l]
      The next time you call each you'll get the next pair out of the hash.

      I get printed only, what the each returns and foreach get ends.

      Update:
      Title updated
[reply]
        Yes, executing that loop only called each once. But if after that loop you put a second loop that calls each, then that second loop will get a second pair out of the hash. Or if you try to iterate through with a while/each loop, you'll get every pair except the one already consumed in the for loop.

        In other words the hash has been left in a potentially bad state.

[reply]
        You most likely want to use something like this: 
        while (($key, $value) = each %$hash_ref) {
    # do something...
}

        [download]
        An example like this is also mentioned in the documentation for each. tilly already explained the reason your loop ends after the first key and value.
[reply]
[d/l]
Re: What is happening ?
by Marshall (Canon) on Aug 19, 2009 at 09:37 UTC
    Not sure what you want:
    There are lots of ways to sort this stuff once we agree on the data to be output. Since $rHol is a reference, you need the -> operator to deference the key, normal hash would be just $Hol{$key}, but you need $rHoL->{$key}. Then you need {} around that whole thing to tell the @ operator what to operate upon.

    #!/usr/bin/perl -w
use strict;

my $hash_ref= {1002=>[1,2,3,4,5],
               1001=>[6,7,8,9,10],
               3   =>[2]};
               
print_HoL($hash_ref);

sub print_HoL
{
   my $rHoL = shift;
   foreach my $key (keys %$rHoL) 
   {
      print "$key: @{$rHoL->{$key}}\n"; 
   }
}
__END__
Prints:
1001: 6 7 8 9 10
1002: 1 2 3 4 5
3: 2

    [download]
[reply]
[d/l]
[select]
Re: problem using foreach and each with hash ref
by sanku (Beadle) on Aug 21, 2009 at 12:34 UTC
    hi, I think it's not that much easy to both key and value pair for hash but you can get either key or value. In my code i used the keys indexes to get the values of hash reference. 
    use strict;
use warnings;
use Data::Dumper;
my $hash_ref={1002=>[1,2,3,4,5],1001=>[6,7,8,9,10],3=>[2]};
my ($hashref,$array_ref,@array,);
foreach $hashref( keys %$hash_ref){
$array_ref=$$hash_ref{$hashref};
@array=@$array_ref;
print "Key = ".$hashref."\tValue = ";
foreach (@array){
print "$_ \t";
}
print "\n";
}

    [download]
[reply]
[d/l]

Back to Seekers of Perl Wisdom