Hello, I do have a follow up question regarding node insertion in doubly linked list. so my intent is to insert a node after the head node and before the last node.
Although I am able to do the insert correctly , when I try to print the output starting from the head . I do not see node that I had inserted before the tail node.
Similarly when I print the output starting from the tail node , I do not see node that I inserted after the head node.

Observe the values printed in the "current" field from my output.

Any corrections/ suggestions which you can provide will be very helpful

here is my code 

#!/usr/bin/perl

use strict;
use warnings;

my $head = {data => 0, prev => undef, next => undef};
my $previous = $head;

open FILE, "<datastored.txt" or die $!;

while (<FILE>){
    chomp;
    $previous->{next} = {
                "data" => $_ , 
                "next" => undef,
                "prev" => $previous,
            };
    $previous = $previous->{next};
    
}

### Inserting element at the beginning of the list after the head node
my $curr = $head;
$curr->{next}= {
                 "data" => 30, 
                "next" => $curr->{next},
                "prev" => $curr,    
};


### Inserting element at the end of the list before the tail node
$curr = $previous;
$curr->{prev}= {
                 "data" => 40, 
                "next" => $curr,
                "prev" => $curr->{prev},    
};


## Printing from head
print "printing from head \n";

 $curr = $head;
while (1) {
    last unless defined $curr->{next};
    print "Current: ", $curr->{data}, 
          "\tPrevious: ", $curr->{prev}{data} // "", 
          "\tNext: ", $curr->{next}{data} // "", "\n";
    $curr = $curr->{next};
}


## printing from tail


print "Printing From tail \n";

while (1) {
    last unless defined $curr->{prev};
    print "Current: ", $curr->{data}, 
          "\tPrevious: ", $curr->{prev}{data} // "", 
          "\tNext: ", $curr->{next}{data} // "", "\n";
    $curr = $curr->{prev};
}

[download]
Output form this program 

printing from head 
Current: 0    Previous:     Next: 30
Current: 30    Previous: 0    Next: line1
Current: line1    Previous: 0    Next: line2
Current: line2    Previous: line1    Next: line3
Current: line3    Previous: line2    Next: line4
Current: line4    Previous: line3    Next: line5


Printing From tail 
Current: line5    Previous: 40    Next: 
Current: 40    Previous: line4    Next: line5
Current: line4    Previous: line3    Next: line5
Current: line3    Previous: line2    Next: line4
Current: line2    Previous: line1    Next: line3
Current: line1    Previous: 0    Next: line2
Current: 0    Previous:     Next: 30

[download]
content of datastored.txt 
line1
line2
line3
line4
line5

[download]

In reply to Re^3: Doubly link list implementation by punitpawar
in thread Doubly link list implementation by punitpawar

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