Syntax:

void SplDoublyLinkedList::add ($index, $newval)

Parameters:It contains two parameters as above and described below:

• $index:stores the index value at which the new element should be inserted.
• $newval:contains an element to be inserted or added.

Returned value:does not return any value.The following programs illustrate the SplDoublyLinkedList::add()function in PHP:Program 1:  
// Declare an empty SplDoublyLinkedList $list = new SplDoublyLinkedList;  
// Use the SplDoublyLinkedList::add() function for
// add elements to SplDoublyLinkedList $list -> add (0, 1); $list -> add (1, " Geeks " ); $list -> add (2, " G " ); $list -> add (3, 10); print_r ( $list ); ?> Exit:

SplDoublyLinkedList Object ( [flags: SplDoublyLinkedList: private] = > 0 [dllist: SplDoublyLinkedList: private] = > Array ([0] = > 1 [1] = > Geeks [2] = > G [3] = > 10))

Program 2:  
// Declare empty SplDoublyLinkedList $list = new SplDoublyLinkedList;  
// Use the SplDoublyLinkedList::add() function for
// add elements to SplDoublyLinkedList $list -> add (0, 30); $list -> add (1, 20); $list -> add (2, 30); $list -> add (3, " Geeks " ); $list -> add (4, ` G` ); print_r ( $list ); ?> Exit:

SplDoublyLinkedList Object ( [flags: SplDoublyLinkedList: private] = > 0 [dllist: SplDoublyLinkedList: private] = > Array ([0] = > 30 [1] = > 20 [2] = > 30 [3] = > Geeks [4] = > G))

Link: https://www.php.net/manual/en/spldoublylinkedlist.add.php