PHP SplDoublyLinkedList::offsetExists() Method: Usage and Examples

Checks whether a specified numeric list offset is present.

The examples focus on the operation itself, including the important distinction: offsetGet fetches an existing value; offsetExists checks availability first.

What It Does

Use the examples below to observe the behavior on a small dataset before extending it to application code.

Syntax and Return Value

SplDoublyLinkedList::offsetExists($index)

The displayed signature describes the API or identifies any correction or optional dependency. When a parameter is optional, supply it only when the task requires it.

Parameters

• index: required.

Example 1: Basic Use

The list begins with 3 values. Notice how offsetExists changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push('tea');
$list->push('coffee');
$list->push('water');
echo $list->offsetExists(1) ? "present" : "missing";

Output from a successful local PHP 8.4 run:

present

Example 2: Checking Behavior

The list begins with 4 values. Notice how offsetExists changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push('one');
$list->push('two');
$list->push('three');
$list->push('four');
echo $list->offsetExists(1) ? "present" : "missing";

Output from a successful local PHP 8.4 run:

present

Example 3: Practical Example

The list begins with 3 values. Notice how offsetExists changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push(4);
$list->push(8);
$list->push(12);
echo $list->offsetExists(2) ? "present" : "missing";

Output from a successful local PHP 8.4 run:

present

Important Behavior and Edge Cases

Offsets are not associative keys; use numeric positions, not arbitrary strings.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Checks whether a specified numeric list offset is present.
• Offsets are not associative keys; use numeric positions, not arbitrary strings.
• offsetGet fetches an existing value; offsetExists checks availability first.

Use SplDoublyLinkedList::offsetExists when its documented behavior matches the problem. Test the relevant edge cases in your own runtime before deploying it.