FIFO table

I want to have table with just 3 records (rows) and i want work it as FIFO

if i add 100
it will go on 1st row
and then if i add 200
it will go in 1st row and 100 should go in 2nd row
and then if i add 300
it will go in 1st row and 200 will go in 2nd row and 100 will go in 3rd row

and when i would add 400 then it would go in 1st row with 300 in 2nd row and 200 in 3rd row but 100 should be deleted.

little complex :)

But i am finding here an easy way to do it.
Thank You.

array_shift()

thanks for the post visualad
but this function doesn't relate to the problem because i want to keep 3 rows (records) in the table and when new record is added last record should be dropped automatically.

Sorry, the function I meant to post was array_unshift. This prepends an element to the front of an array. The type of FIFO you are asking for is a pipe as a normal FIFO structure grows in size similar to how a queue inside a shop grows.

If you were to describe this pipe using an object, you could have something like this:

PHP Code:

---

class Pipe
{
    private $pipeArray;
    private $size;
    private $pointer = 0;

    public function __construct($size)
    {
        $this->size = (int) $size;
        $this->pipeArray = Array($this->size);
    }

    /**
     * Adds data to the pipe. If the pipe has reached its maximum
     * size the first element in the pipe is returned and removed from the
     * pipe to make room for the new element.
     */
    public function push($data)
    {
        $first = null;

        if ($this->pointer == $this->size - 1) { // pipe is full
            $first = array_pop($this->pipeArray);
        } else {
            ++$this->pointer;
        }         

        array_unshift($this->pipeArray, $data); // add the data    

        return $first;
    }

    /**
     * Pulls the first element from the pipe, reducing its contents by 1.
     */
    public function pop()
    {
        $data = null;

        if ($this->pointer != 0) {
            --$this->pointer;
            $data = array_pop($this->pipeArray);
        }

        return $data;
    }

    /**
     * Returns the current pipe as an array.
     */
    public function get_pipe_as_array()
    {
        return array_reverse($this->pipeArray);
    }
} 


---

The object can then be used as follows:

PHP Code:

---

$pipe = new Pipe(3); // makes a pipe containing 3 elements
$pipe->push(100);
$pipe->push(200);
$pipe->push(300); // pipe should now be full
$pipe->push(400);

print_r($pipe->get_pipe_as_array()); 


---

Note, that the array is returned in reverse order, so you can traverse it using a foreach loop and it will maintain the FIFO nature of the pipe.