PHP mb_strtolower: How to Handle Multibyte Strings Properly

The mb_strtolower() function in PHP turns every letter in a string into lowercase. It works with multibyte encodings like UTF-8.

Understand the PHP mb_strtolower Function

The strtolower() only works with single-byte characters. If you use it on a UTF-8 string, it may break non-English letters. mb_strtolower() fixes that. It handles letters from many languages.

Here is the syntax:

mb_strtolower(string $string, ?string $encoding = null)

Parameters:

• $string
  • The input string you want to convert to lowercase.
  • It must be a multibyte-encoded string if you’re working with non-ASCII characters (e.g., UTF-8).
  • Example: "TÜRKÇE" or "Пример".
• $encoding
  • The character encoding of the string (e.g., "UTF-8", "ISO-8859-1").
  • If set to null, PHP uses the internal character encoding, which you can define using mb_internal_encoding().

It returns the lowercase version of the input string with a string type. It respects the character encoding.

Here is a quick example:

echo mb_strtolower("HELLO WORLD", 'UTF-8'); 

Here are the Use Cases:

• Normalize user input
• Handle email comparisons
• Create case-insensitive search
• Store lowercase data for multilingual apps

Languages like Turkish, Russian, and Chinese use multibyte characters. PHP does not handle them well without help. The mbstring extension helps with that. mb_strtolower() reads each character properly.

To lower UTF-8 text, pass the string and “UTF-8” as encoding:

$text = "GÜNAYDIN"; // Turkish for "Good Morning"
echo mb_strtolower($text, 'UTF-8'); 

The output:

günaydin

Here are key differences of mb_strtolower() vs strtolower() in PHP:

• strtolower() breaks with multibyte strings
• mb_strtolower() handles characters like ü, ğ, ş
• strtolower() works for basic English
• mb_strtolower() supports Unicode

Examples of mb_strtolower Function in PHP

Use mb_strtolower() with the right encoding:

$word = "Straße"; // German for "street"
echo mb_strtolower($word, 'UTF-8'); 

Output:

straße

Lowercase Turkish or German characters with PHP mb_strtolower():

Turkish uses letters like İ and ğ. German has ß. strtolower() does not convert these correctly. mb_strtolower() does:

echo mb_strtolower("İSTANBUL", 'UTF-8'); 

Output:

istanbul

Wrapping Up

In this article, you learned what the mb_strtolower() function does and how it solves the problem of converting multibyte strings to lowercase in PHP. You also saw how it differs from strtolower() and why it works better with non-English letters.

Here is a quick recap:

• mb_strtolower() turns every letter in a string to lowercase and works with multibyte encodings like UTF-8.
• It is better than strtolower() when you deal with languages like Turkish, German, or Russian.
• You must pass the right encoding to make it work as expected.
• It helps normalize user input, compare emails, build search features, and store data in lowercase.
• Always use it when handling non-ASCII text in PHP.

FAQs

Does mb_strtolower() support all languages?

It supports many but not all. It works well with most characters in Unicode.

How to change the default encoding for mb_strtolower()?

Use this:

mb_internal_encoding("UTF-8");

This sets UTF-8 for all mbstring functions.

What are common errors when you use mb_strtolower()?

You may forget to set encoding and may not install the mbstring extension. You may pass null or wrong type.

Can mb_strtolower() be used without the mbstring extension?

No. It comes from mbstring. If mbstring is missing, you get a fatal error.

How do I check if mbstring Is enabled in PHP?

Call:

phpinfo();

Or check:

extension_loaded('mbstring');