PHP array_fill Function

last modified March 13, 2025

The PHP array_fill function creates an array filled with a specified value. It's useful for initializing arrays with default values.

Basic Definition

The array_fill function generates an array with values. It starts at a specified index and fills the array with the given value.

Syntax: array_fill(int $start_index, int $count, mixed $value): array. The function returns a new array with $count elements.

Basic array_fill Example

This demonstrates creating a simple array filled with a default value.

basic_array_fill.php

<?php

$filledArray = array_fill(0, 5, 'default');

print_r($filledArray);

This creates an array with 5 elements, all set to 'default'. The array starts at index 0. The output shows all elements have the same value.

Negative Start Index

array_fill can create arrays with negative starting indices.

negative_index.php

<?php

$negativeArray = array_fill(-3, 4, 'item');

print_r($negativeArray);

This creates an array starting at index -3 with 4 elements. The resulting array will have keys -3, -2, -1, and 0, all filled with 'item'.

Filling with Different Data Types

The function can fill arrays with any data type, including objects.

data_types.php

<?php

$numberArray = array_fill(0, 3, 42);
$boolArray = array_fill(0, 2, true);
$objectArray = array_fill(0, 2, new stdClass());

print_r($numberArray);
print_r($boolArray);
print_r($objectArray);

This shows arrays filled with integers, booleans, and objects. Note that object elements will be references to the same object instance.

Multi-dimensional Arrays

array_fill can be used to create multi-dimensional arrays.

multi_dimensional.php

<?php

$matrix = array_fill(0, 3, array_fill(0, 3, 0));

print_r($matrix);

This creates a 3x3 matrix filled with zeros. The outer array_fill creates an array where each element is another array filled with zeros.

Combining with array_fill_keys

array_fill can be combined with other array functions.

combined.php

<?php

$keys = ['a', 'b', 'c'];
$filled = array_fill_keys($keys, array_fill(0, 3, null));

print_r($filled);

This creates an associative array where each key maps to a sub-array filled with null values. It demonstrates combining array_fill with array_fill_keys.

Best Practices

Memory Usage: Be cautious with large arrays as they consume memory.
Object References: Remember all object elements reference the same instance.
Negative Indices: Useful for specific use cases but can be confusing.
Performance: Faster than manual loops for array initialization.

Source

PHP array_fill Documentation

This tutorial covered the PHP array_fill function with practical examples showing its usage for array initialization 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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