class SplDoublyLinkedList implements Iterator, Traversable, Countable, ArrayAccess {
        const IT_MODE_LIFO = 2;
        const IT_MODE_FIFO = 0;
        const IT_MODE_DELETE = 1;
        const IT_MODE_KEEP = 0;


        /**
         * Add/insert a new value at the specified index
         * @param mixed $index The index where the new value is to be inserted.
         * @param mixed $newval The new value for the index.
         * @link http://php.net/spldoublylinkedlist.add
         * @return void
         * @since 5.5.0
         */
        public function add($index, $newval) {}

        /**
         * Pops a node from the end of the doubly linked list  
         * @link http://php.net/manual/en/spldoublylinkedlist.pop.php
         * @return mixed The value of the popped node.
         * @since 5.3.0
         */
        public function pop () {}

        /**
         * Shifts a node from the beginning of the doubly linked list  
         * @link http://php.net/manual/en/spldoublylinkedlist.shift.php
         * @return mixed The value of the shifted node.
         * @since 5.3.0
         */
        public function shift () {}

        /**
         * Pushes an element at the end of the doubly linked list
         * @link http://php.net/manual/en/spldoublylinkedlist.push.php
         * @param mixed $value <p>
         * The value to push.
         * </p>
         * @return void 
         * @since 5.3.0
         */
        public function push ($value) {}

        /**
         * Prepends the doubly linked list with an element
         * @link http://php.net/manual/en/spldoublylinkedlist.unshift.php
         * @param mixed $value <p>
         * The value to unshift.
         * </p>
         * @return void 
         * @since 5.3.0
         */
        public function unshift ($value) {}

        /**
         * Peeks at the node from the end of the doubly linked list
         * @link http://php.net/manual/en/spldoublylinkedlist.top.php
         * @return mixed The value of the last node.
         * @since 5.3.0
         */
        public function top () {}

        /**
         * Peeks at the node from the beginning of the doubly linked list
         * @link http://php.net/manual/en/spldoublylinkedlist.bottom.php
         * @return mixed The value of the first node.
         * @since 5.3.0
         */
        public function bottom () {}

        /**
         * Counts the number of elements in the doubly linked list.
         * @link http://php.net/manual/en/spldoublylinkedlist.count.php
         * @return int the number of elements in the doubly linked list.
         * @since 5.3.0
         */
        public function count () {}

        /**
         * Checks whether the doubly linked list is empty.
         * @link http://php.net/manual/en/spldoublylinkedlist.isempty.php
         * @return bool whether the doubly linked list is empty.
         * @since 5.3.0
         */
        public function isEmpty () {}

        /**
         * Sets the mode of iteration
         * @link http://php.net/manual/en/spldoublylinkedlist.setiteratormode.php
         * @param int $mode <p>
         * There are two orthogonal sets of modes that can be set:
         * </p>
         * The direction of the iteration (either one or the other):
     * <b>SplDoublyLinkedList::IT_MODE_LIFO</b> (Stack style)
         * @return void 
         * @since 5.3.0
         */
        public function setIteratorMode ($mode) {}

        /**
         * Returns the mode of iteration
         * @link http://php.net/manual/en/spldoublylinkedlist.getiteratormode.php
         * @return int the different modes and flags that affect the iteration.
         * @since 5.3.0
         */
        public function getIteratorMode () {}

        /**
         * Returns whether the requested $index exists
         * @link http://php.net/manual/en/spldoublylinkedlist.offsetexists.php
         * @param mixed $index <p>
         * The index being checked.
         * </p>
     * @return bool true if the requested <i>index</i> exists, otherwise false
         * @since 5.3.0
         */
        public function offsetExists ($index) {}

        /**
         * Returns the value at the specified $index
         * @link http://php.net/manual/en/spldoublylinkedlist.offsetget.php
         * @param mixed $index <p>
         * The index with the value.
         * </p>
     * @return mixed The value at the specified <i>index</i>.
         * @since 5.3.0
         */
        public function offsetGet ($index) {}

        /**
         * Sets the value at the specified $index to $newval
         * @link http://php.net/manual/en/spldoublylinkedlist.offsetset.php
         * @param mixed $index <p>
         * The index being set.
         * </p>
         * @param mixed $newval <p>
     * The new value for the <i>index</i>.
         * </p>
         * @return void 
         * @since 5.3.0
         */
        public function offsetSet ($index, $newval) {}

        /**
         * Unsets the value at the specified $index
         * @link http://php.net/manual/en/spldoublylinkedlist.offsetunset.php
         * @param mixed $index <p>
         * The index being unset.
         * </p>
         * @return void 
         * @since 5.3.0
         */
        public function offsetUnset ($index) {}

        /**
         * Rewind iterator back to the start
         * @link http://php.net/manual/en/spldoublylinkedlist.rewind.php
         * @return void 
         * @since 5.3.0
         */
        public function rewind () {}

        /**
         * Return current array entry
         * @link http://php.net/manual/en/spldoublylinkedlist.current.php
         * @return mixed The current node value.
         * @since 5.3.0
         */
        public function current () {}

        /**
         * Return current node index
         * @link http://php.net/manual/en/spldoublylinkedlist.key.php
         * @return mixed The current node index.
         * @since 5.3.0
         */
        public function key () {}

        /**
         * Move to next entry
         * @link http://php.net/manual/en/spldoublylinkedlist.next.php
         * @return void 
         * @since 5.3.0
         */
        public function next () {}

        /**
         * Move to previous entry
         * @link http://php.net/manual/en/spldoublylinkedlist.prev.php
         * @return void 
         * @since 5.3.0
         */
        public function prev () {}

        /**
         * Check whether the doubly linked list contains more nodes  当前指针处元素是否有效
         * @link http://php.net/manual/en/spldoublylinkedlist.valid.php
         * @return bool true if the doubly linked list contains any more nodes, false otherwise.
         * @since 5.3.0
         */
        public function valid () {}

        /**
         * Unserializes the storage
         * @link http://php.net/manual/ru/spldoublylinkedlist.serialize.php
         * @param string $serialized The serialized string.
         * @return void
         * @since 5.4.0
         */
         public function unserialize($serialized) {}

         /**
         * Serializes the storage
         * @link http://php.net/manual/ru/spldoublylinkedlist.unserialize.php
         * @return string The serialized string.
         * @since 5.4.0
         */
         public function  serialize () {}

}

<?php
header("Content-type: text/html; charset=gb2312");
$doubly=new SplDoublyLinkedList();
$doubly->push(‘a‘);
$doubly->push(‘b‘);
$doubly->push(‘c‘);
$doubly->push(‘d‘);
$doubly->add(1,‘e‘);

echo ‘Original:‘."\n";
var_dump($doubly);

echo ‘FIFO|KEEP:‘."\n";
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO | SplDoublyLinkedList::IT_MODE_KEEP);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
    echo $key.‘ ‘.$value."\n";
}

echo ‘LIFO|KEEP:‘."\n";
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_KEEP);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
    echo $key.‘ ‘.$value."\n";
}

echo ‘LIFO|DELETE:‘."\n";
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_DELETE);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
    if($key == 1) break;
    echo $key.‘ ‘.$value."\n";
}
echo ‘List after Delete‘."\n";
var_dump($doubly);
?>