PHP sizeof Function

last modified March 13, 2025

The PHP sizeof function returns the number of elements in an array. It's an alias of count and works identically.

Basic Definition

The sizeof function counts all elements in an array or countable object. It returns the number of elements as an integer.

Syntax: sizeof(array|Countable $value, int $mode = COUNT_NORMAL): int. The optional mode parameter can be COUNT_RECURSIVE for multidimensional arrays.

Basic sizeof Example

This demonstrates counting elements in a simple indexed array.

basic_sizeof.php

<?php

$fruits = ['apple', 'banana', 'orange'];
$count = sizeof($fruits);

echo "The array contains $count fruits";

This counts the elements in the $fruits array. The function returns 3, which matches the number of elements in the array.

Associative Array Size

sizeof works with associative arrays the same way as with indexed arrays.

associative_array.php

<?php

$user = [
    'name' => 'John Doe',
    'email' => 'john@example.com',
    'age' => 30
];

$fieldCount = sizeof($user);

echo "User has $fieldCount fields";

This counts the key-value pairs in an associative array. The function returns 3 regardless of whether the array is indexed or associative.

Multidimensional Array Counting

Using COUNT_RECURSIVE mode counts all elements in nested arrays.

multidimensional_array.php

<?php

$matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];

$normalCount = sizeof($matrix);
$recursiveCount = sizeof($matrix, COUNT_RECURSIVE);

echo "Normal count: $normalCount\n"; 
echo "Recursive count: $recursiveCount";

Normal mode counts only the top-level arrays (3). Recursive mode counts all elements including nested ones (9 numbers + 3 arrays = 12).

Empty Array Behavior

sizeof returns 0 for empty arrays, which is useful for checking.

empty_array.php

<?php

$emptyArray = [];
$count = sizeof($emptyArray);

if ($count === 0) {
    echo "The array is empty"; 
}

This demonstrates that sizeof correctly identifies empty arrays by returning 0. This is helpful for validation checks in code.

Counting Objects

sizeof can count objects that implement the Countable interface.

countable_object.php

<?php

class Cart implements Countable {
    private $items = [];
    
    public function add($item) {
        $this->items[] = $item;
    }
    
    public function count(): int {
        return sizeof($this->items);
    }
}

$cart = new Cart();
$cart->add('Product 1');
$cart->add('Product 2');

echo "Cart has " . sizeof($cart) . " items";

This shows sizeof working with a Countable object. The Cart class implements the interface and provides its own counting logic.

Best Practices

Consistency: Prefer count for readability.
Performance: Both sizeof and count are O(1).
Type Safety: Check is_countable() before counting.
Empty Checks: Use empty() when just checking for emptiness.

Source

PHP sizeof Documentation

This tutorial covered the PHP sizeof function with practical examples showing its usage for counting array elements in various scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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