SplDoublyLinkedList::valid

(PHP 5 >= 5.3.0, PHP 7)

SplDoublyLinkedList::valid — Check whether the doubly linked list contains more nodes

说明

public SplDoublyLinkedList::valid ( void ) : bool

Checks if the doubly linked list contains any more nodes.

参数

此函数没有参数。

返回值

Returns TRUE if the doubly linked list contains any more nodes, FALSE otherwise.

User Contributed Notes

phpdude at zootal dot com 23-Aug-2017 09:40
The docs say "Check whether the doubly linked list contains more nodes". I do not believe this is correct.

Example:

$dlist = new SplDoublyLinkedList;
$data=[1,2,3,4,5];

foreach($data as $d)
    $dlist->push($d);
$dlist->rewind();

for($i=0;$i<6;$i++)
{
    $currentValue = $dlist->current();
    $currentValid = $dlist->valid();

    $status = $currentValid ? 'True' : 'False';
    echo 'Current value is: ' . $currentValue . ' Valid status is: ' . $status . "\n";

    $dlist->next();
}

Output:

Current value is: 1 Valid status is: True
Current value is: 2 Valid status is: True
Current value is: 3 Valid status is: True
Current value is: 4 Valid status is: True
Current value is: 5 Valid status is: True
Current value is:  Valid status is: False

Note that when we are on the last node of the list, value = 5, the valid() function returns true. Yet we are on the last node of the list, and there are no more nodes. If the valid() function were checking to see if there were any more nodes on the list, it would return false, not true.

If you look at the docs for Iterator::valid, they say "Checks if current position is valid". I believe that is in fact what valid() does, it checks to see if the *current* position is valid, *not* if there are any more nodes.

Be aware of this or it will bite you. You can happily iterate to the end of the list, run valid(), think there is one more node, do a next(), grab the value, and you get null instead of the last node of the list.
lincoln dot du dot j at gmail dot com 11-Jul-2017 05:39
$a = new SplDoublyLinkedList;
$arr=[1,2,3,4,5,6,7,8,9];

for($i=0;$i<count($arr);$i++){
    $a->add($i,$arr[$i]);
}

$a->rewind();

while($a->valid()){
    echo 'key ', $a->key(), ' value ', $a->current(),"\n";
    $a->next();
}