How to add padding to a string with str_pad
Jul 13, 2025 am 01:56 AMThe str_pad() function of PHP is used to add padding characters at both ends of a string to reach the specified length. Its syntax is str_pad($input, $pad_length, $pad_string = " ", $pad_type = STR_PAD_RIGHT); 1. The basic usage is to make up the length, such as str_pad("42", 5, "0", STR_PAD_LEFT) and output "00042"; 2. The filling direction can be controlled, including the right (default), left or both sides, such as str_pad("hello", 10, "-", STR_PAD_BOTH) and output "--hello---"; 3. The padding character can be any character, such as str_pad("Warning!", 15, "*", STR_PAD_BOTH) output "***Warning!****"; 4. Notes include: setting the length is less than the original string without truncation, the order when multi-character filling, and multi-byte characters are recommended to use mb_str_pad() to handle it.
Sometimes you need to add some extra characters at the beginning or end of the string, such as zeroing or aligning text. PHP provides a very convenient function str_pad()
to complete this task, which is simple but practical.

Let’s take a look at some common usage methods.
1. Basic usage: add fixed length padding to strings
The most basic function of str_pad()
is to make the string reach a specified length, and the insufficient parts are filled with the characters you provide. The syntax is as follows:

str_pad($input, $pad_length, $pad_string = " ", $pad_type = STR_PAD_RIGHT)
For example, suppose you want a numeric string to always display as a 5-digit number:
echo str_pad("42", 5, "0", STR_PAD_LEFT); // Output "00042"
This allows for easy numbering, time alignment and other operations.

2. Control the filling direction: left, right or both sides?
By default, padding is added to the right of the string. But you can control the position of the padding through the fourth parameter:
-
STR_PAD_RIGHT
(default): Fill on the right -
STR_PAD_LEFT
: Fill on the left -
STR_PAD_BOTH
: The two sides are filled evenly. If the total length is not enough to be averaged, the left side will be less
for example:
echo str_pad("hello", 10, "-", STR_PAD_BOTH); // Output "--hello---"
Note that the two sides are not completely symmetrical, because 10 - 5 = 5, add two and three symbols on each left and right.
3. Filling content is not just spaces or numbers
Although the most common use is space or zero, you can use any character as fill content. For example:
echo str_pad("Warning!", 15, "*", STR_PAD_BOTH); // Output "***Warning!****"
It can also be used to create simple text borders or decorative effects, suitable for command line output or log information beautification.
4. Precautions and FAQs
There are a few small details that are prone to errors:
- If the set length is shorter than the original string, it will not be truncated, but will directly return to the original string.
- The third parameter can be multiple characters, such as
"*-"
, but pay attention to the loop order. - Multi-byte characters (such as Chinese) may cause inconsistent calculation lengths. It is recommended to use them in conjunction with
mb_str_pad()
at this time.
So before using it, confirm whether your string encoding is unified to avoid unexpected results.
Basically, that's not complicated to use but practical, especially when dealing with formatted output, it can save a lot of trouble.
The above is the detailed content of How to add padding to a string with str_pad. For more information, please follow other related articles on the PHP Chinese website!

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