The SplDoublyLinkedList::valid() function is an inbuilt function in PHP which is used to check whether the doubly linked list contains more nodes or not.
Syntax:
bool SplDoublyLinkedList::valid( void )
Parameters: This function does not accept any parameters.
Return Value: This function returns TRUE if the doubly linked list contains any more nodes and FALSE otherwise.
Below programs illustrate the SplDoublyLinkedList::valid() function in PHP:
Program 1:
<?php    // Declare an empty SplDoublyLinkedList $list = new SplDoublyLinkedList();    // Use SplDoublyLinkedList::push() function to  // add elements to the SplDoublyLinkedList $list->push(1); $list->push(2); $list->push(3); $list->push(8); $list->push(5);   $list->rewind();   for($i = 0; $i < 5; $i++) {     if($list->valid())         echo $list->current() . " ";           $list->next(); }   ?> |
Output:
1 2 3 8 5
Program 2:
<?php    // Declare an empty SplDoublyLinkedList $list = new SplDoublyLinkedList();    // Use SplDoublyLinkedList::add() function // to add the element into the list $list->add(0, "Welcome"); $list->add(1, "to"); $list->add(2, "neveropen"); $list->add(3, "A"); $list->add(4, 'Computer'); $list->add(5, "Science"); $list->add(6, 'Portal');    $list->rewind();   for($i = 0; $i < 7; $i++) {     if($list->valid())         echo $list->current() . " ";           $list->next(); }   ?> |
Output:
Welcome to neveropen A Computer Science Portal
Reference: https://www.php.net/manual/en/spldoublylinkedlist.valid.php
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