How to Use str_pad in PHP: Syntax and Examples

Use str_pad in PHP to add characters to a string until it reaches a specified length. It takes the original string, target length, padding string, and padding type (left, right, or both) as arguments.

Syntax

The str_pad function has four parameters:

• input: The original string you want to pad.
• pad_length: The total length of the resulting string after padding.
• pad_string (optional): The string used for padding. Defaults to a space.
• pad_type (optional): Where to add the padding. Use STR_PAD_RIGHT (default), STR_PAD_LEFT, or STR_PAD_BOTH.

php

str_pad(string $input, int $pad_length, string $pad_string = " ", int $pad_type = STR_PAD_RIGHT): string

Example

This example shows how to pad the string "cat" to length 7 using different padding types and characters.

php

<?php
// Original string
$word = "cat";

// Pad right with spaces (default)
echo str_pad($word, 7) . "\n";

// Pad left with dots
echo str_pad($word, 7, ".", STR_PAD_LEFT) . "\n";

// Pad both sides with dashes
echo str_pad($word, 7, "-", STR_PAD_BOTH) . "\n";
?>

Output

cat    
....cat
--cat--

Common Pitfalls

Common mistakes include:

• Setting pad_length shorter than the original string length, which returns the original string unchanged.
• Using an empty string for pad_string, which causes a warning and no padding.
• Forgetting to specify pad_type when you want padding on the left or both sides.

php

<?php
// Wrong: pad_length less than string length
echo str_pad("hello", 3, "*") . "\n"; // outputs 'hello'

// Wrong: empty pad_string
// echo str_pad("hi", 5, "") . "\n"; // Warning: pad_string cannot be empty

// Right: specify pad_type for left padding
echo str_pad("hi", 5, "*", STR_PAD_LEFT) . "\n";
?>

Output

hello
***hi

Quick Reference

Parameter	Description	Default
input	The string to pad	Required
pad_length	Length of the final string	Required
pad_string	String used for padding	Space (" ")
pad_type	Where to pad: right, left, or both	STR_PAD_RIGHT

Key Takeaways

Use str_pad to extend a string to a desired length by adding characters.

Specify pad_type to control padding direction: right, left, or both sides.

pad_string defaults to space but can be any string of characters.

If pad_length is less than the string length, the original string is returned.

Avoid empty pad_string to prevent warnings.