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

How Can I reset the internal pointer of a while loop back to the first element in the list? I'm trying to use a redo from a for loop to another for loop which has a while loop in between them, but the internal pointer of the while loop remains the same instead of starting at the beginning element again. udpate: code follows 
MASK: while (my($defNet,$defKey) = each (%defMaskArray)){
    print OUT "Starting new Subnet - $defNet\n";
    $boundary = $defKey; # set boundary to key by default and allow fo
+r it to be modified
    print OUT "Working:  $defNet maskKey $boundary for $subCount{$defN
+et} hosts\n";
    my $refHandle = $subArray{$defNet}; # create a hash reference for 
+the subnet subHash
    my $hostsN = $subCount{$defNet}; # get number of hosts from subCou
+nt hash
    HOST:  for ($b = 1; $b <= $hostsN; $b++){ # track number of hosts 
+in Subnet so we know when to stop
        print OUT "Current iteration is $b\n";
        NET:  while (my($n, $host) = each %$refHandle){ # loop through
+ hosts in subnet subhash
            print OUT "| Subnet:  ".$defNet."| Original Mask:  $defKey
+"."| Current Mask:  ".$boundary."| IP:  ".$host."| host #:  $b"."\n";
            TEST:  for ($i = 0; $i <= 256; $i = ($i + $boundary)){ # e
+valuate boundaries
                if ($i == $host || (($i + $boundary) - 1) == $host){
                    print OUT "$defNet for $host fell on a boundary fo
+r mask - $boundary\n";
                    if ($boundary == 256){
                        print OUT "Current Sub: $defNet Mask: 256\n";
                        push (@routeArray, $defNet."/24")
                    }
                    else{
                        $boundary = ($boundary * 2);
                        print OUT "test for $host failed - retrying wi
+th $boundary after $b hosts attempted - original was $defKey\n";
                        $i = 0;
                        redo HOST;
                    }
                }
                elsif ($i > $host){
                    print OUT "$i is Greater then $host, no need to te
+st further. Value of B is $b. Next Host.\n";
                    next HOST;
                }
                else{
                    print OUT "Host $host passed for $i - this is host
+ # $b with a default of $defKey\n";
                }
            }
        }
        print OUT "# of Hosts:  ".$b." Original Mask:  ".$defKey." New
+ Mask:  ".$boundary."\n";
        print OUT "#################################################\n
+";
        $trueMaskArray{$defNet} = $boundary;
    }
}

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Replies are listed 'Best First'.
Re: Resetting Internal Loop Pointers
by moritz (Cardinal) on Nov 28, 2007 at 19:35 UTC
    Since while only tests a condition, perl has no knowledge of what you consider the "loop pointer".

    You'll have to reset it yourself, of use a for loop (perhaps with a label) instead. Or rethink your code...

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Re: Resetting Internal Loop Pointers
by wind (Priest) on Nov 28, 2007 at 20:02 UTC
    Simply change your while to a for loop if each is giving you problems with redo: 
    MASK:
for my $defNet (keys %defMaskArray) {
    my $defKey = $defMaskArray{$defNet};
    
    #...
    
    redo MASK if $defKey eq 'foobar';
    
    #...
}

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    - Miller
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Re: Resetting Internal Loop Pointers
by jrsimmon (Hermit) on Nov 28, 2007 at 20:24 UTC
    If you want a finer level of control than a redo, you can pull the keys function out of the loop and then iterate over an array with a counter. Then you will have the ability to manipulate the counter however you wish. Here's a simplistic example:
    use strict;

my %hash = (test1 => 1, test2 => 2, test3 => 3, test4 => 4);
my @array = sort(keys(%hash));
my $counter = 0;
my $resetter = undef;
my $resets = 0;

while($counter <= $#array){
  if(defined($resetter)){
    $counter = 0;
    $resets++;
  }
  $resetter = undef;
  print $hash{@array[$counter]};
  $counter++;
  $resetter = 1 if $counter > 2 and $resets < 2;
}

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    If all you need is the ability to restart the loop, the for/redo suggestion above requires a smaller code change.
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Re: Resetting Internal Loop Pointers
by GrandFather (Saint) on Nov 29, 2007 at 00:18 UTC

    You need to reset the each iterator. Using keys does that. Refactoring your code a little may help see what's going on. Consider:

    use strict;

while (my ($defNet, $defKey) = each (%defMaskArray)) {
    ...

HOST:
    for (my $bCount = 1; $bCount <= $hostsN; $bCount++) {
        ...
        while (my ($n, $host) = each %$refHandle) {
            ...
        
        my $testResult = test ($bCount, $boundary, $host, $defNet, $de
+fKey, \@routeArray);
        
        keys %$refHandle if $testResult ne 'ok'; # Reset each
        redo HOST if $testResult eq 'retry';
        next HOST if $testResult eq 'greater';
        }
        
        ...
    }
}

sub test {
    my ($bCount, $boundary, $host, $defNet, $defKey, $routeArray, ) = 
+@_;
    
    for (my $iCount = 0; $iCount <= 256; $iCount = ($iCount + $boundar
+y)) {
        # evaluate boundaries
        if ($iCount == $host || (($iCount + $boundary) - 1) == $host) 
+{
            print OUT
                "$defNet for $host fell on a boundary for mask - $boun
+dary\n";
            if ($boundary == 256) {
                ...
            } else {
                ...
                return 'retry';
            }
        } elsif ($iCount > $host) {
            ...
            return 'greater';
        } else {
            ...
        }
    }
    
    return 'ok';
}

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    Note too that you should use strictures (use strict; use warnings;) and generally avoid using $a and $b except for their magical use in the context of sort.

    Perl is environmentally friendly - it saves trees
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