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Linked list data structure in PHP?

I'm wondering how can I use pointers in PHP. I've experience in C with pointers and creating data structures like lists, linked lists (chains) and similar, and now I want to do these in PHP. The first thing I've read about references are that they ARE NOT pointers :)
I'm interested if PHP can do structs?
*sigh* Why all PHP learning books write only about making SQL queries and writing HTML :(

In PHP4 or 5 you would set up a class, which would give you an object. You can use the object like a struct, if that is what you want to do. You also can do indirection with PHP. The syntax is not nearly so elegant as C pointer syntax, but it is possible.

In PHP 5, everything is now passed-by-reference, which is good, because it makes making data structures simpler. In PHP4, when you would pass an object to a function, it only passed a value (a copy, essentially). So, any where you wanted to pass an object by reference, you had to use an & (ampersand), but, with PHP, it becamse pretty easy to accidently make a copy instead. The main point is, if you plan on supporting PHP4, it'll take a bit more work and be a bit uglier. PHP5 references are not pointers per se, no, but they are used in the way you expect. Anyways, here is part of a simple linked list in PHP5.

Code:

class LinkedList {

  private $head = null;

  private $tail = null;

  private $size = 0;



  public function __construct()

  {

  }



  public function add($data)

  {

    $node = new Node($data);

    if (is_null($this->tail)) {

      $this->head = $this->tail = $data;

      $this->size++;

      return;

    }



    $this->tail->next = $node;

    $node->prev = $this->tail;

    $this->tail = $node;

    $this->size++;

  }



  // ... more functionality goes here

}



class Node {

  public $data = null;

  public $prev = null;

  public $next = null;



  public function __construct($data = null)

  { 

    $this->data = $data;

  }

}

Quote:

Originally Posted by ivanatora (Post 2867959)

*sigh* Why all PHP learning books write only about making SQL queries and writing HTML :(

98% of the people who are programming with PHP only want to do that.

Thank you!
I'd better sit on these classes.

In the strict sense of the definition a reference is not a pointer, however it is a way of referring to another variable and so from a data structures view point it performs the task of a pointer. Many years ago I wrote some code in PHP illustrating how the basic data structures work, so it's possible, and yes I used the class approach suggested by the previous posters.

Just for clearance, I believe that line of your code:

Code:

$this->head = $this->tail = $data;

Must be changed with that:

Code:

$this->head = $this->tail = $node;

If I'm right, I've began to get the point :)

Yahoo! My first PHP stack:

Code:

<?php

class Node {

        var $next,$data;

        function Node($data){

                $this->next = null;

                $this->data = $data;

        }

}      



class Stack {

        function Stack(){

        }

        var $sp = null;

        function push($data){

                $node = new Node($data);

                $node->next = $this->sp;

                $this->sp = $node;

        }

        function pop(){

                if ($this->sp == null) return;

                $tmp = $this->sp;

                //print $tmp->data . "\n";

                $this->sp = $this->sp->next;

                return $tmp->data;

        }

}

$st = new Stack();



$str = "begin";

while (strcmp("end",$str) != 0){

        print "IN: ";

        $str = trim(fgets(STDIN));

        $st->push($str);

}

print_r($st);

$tmp = $st->pop();

while ($tmp != null){

        print $tmp . "\n";

        $tmp = $st->pop();

}

?>

That looks correct to me, although I've not tried to run it! What I would say is that the constructor you are using is PHP4 syntax, in PHP5 they changed it to be __construct(), if you have access to PHP5 I'd use that because it has much better OO support.