Master PHP’s array_fill(): Quick Guide to Fill Arrays Efficiently

In PHP's function library, the array_fill() function is a useful tool for filling an array with a specified number of elements, allowing you to define both keys and values.

Function Signature

array_fill(int $start_index, int $num, mixed $value): array

Parameter Explanation

$start_index

: The starting index of the array, must be a non‑negative integer. $num: The number of elements to fill, must be a non‑negative integer. $value: The value to fill, can be any scalar type; it must be a scalar.

Return Value

Returns an array containing the filled elements within the specified range.

Usage Examples

Example 1 – Fill an array with ten elements of value 1:

<?php
// Fill an array with 10 elements, each value 1
$arr = array_fill(0, 10, 1);
print_r($arr);
?>

Output:

Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 1
    [4] => 1
    [5] => 1
    [6] => 1
    [7] => 1
    [8] => 1
    [9] => 1
)

Example 2 – Use letters as keys:

<?php
// Use letters as keys to fill the array
$arr = array_fill('a', 5, 'hello');
print_r($arr);
?>

Output:

Array
(
    [a] => hello
    [b] => hello
    [c] => hello
    [d] => hello
    [e] => hello
)

Important Notes

$start_index

must be a non‑negative integer; otherwise a warning is raised. $num must be a non‑negative integer; otherwise a warning is raised. $value must be a scalar; using non‑scalar values triggers a warning.

When using alphabetic keys, ensure the sequence is correct to avoid misalignment.

If the number of elements is zero, the function returns an empty array.

Filling a very large number of elements may consume significant memory.

Conclusion

The array_fill() function provides a quick way to populate arrays without manual loops, requiring only the start index, number of elements, and the fill value. Proper parameter usage prevents errors and optimizes performance.