PHP – Case folding in a string using mb_convert_case()

The mb_convert_case() function is an inbuilt PHP function used to perform case folding on a given string. It supports multibyte character encodings and offers various conversion modes for different case transformations.

Syntax

string mb_convert_case(string $string, int $mode, ?string $encoding = null)

Parameters

The mb_convert_case() function accepts three parameters ?

• $string − The input string to be converted.

• $mode − The conversion mode. Available constants include:

  • MB_CASE_UPPER − Convert to uppercase
  • MB_CASE_LOWER − Convert to lowercase
  • MB_CASE_TITLE − Convert to title case
  • MB_CASE_FOLD − Case folding (PHP 7.3+)
  • MB_CASE_UPPER_SIMPLE − Simple uppercase (PHP 7.3+)
  • MB_CASE_LOWER_SIMPLE − Simple lowercase (PHP 7.3+)

• $encoding − Optional character encoding. If omitted, the internal character encoding is used.

Return Value

Returns the converted string according to the specified mode.

Example 1 - Basic Case Conversion

<?php
    $string = "Hello World!, Welcome to the online Tutorial";

    // Convert to uppercase
    $upper = mb_convert_case($string, MB_CASE_UPPER, "UTF-8");
    echo "Uppercase: " . $upper . "<br>";

    // Convert to lowercase
    $lower = mb_convert_case($string, MB_CASE_LOWER, "UTF-8");
    echo "Lowercase: " . $lower . "<br>";
?>

Uppercase: HELLO WORLD!, WELCOME TO THE ONLINE TUTORIAL
Lowercase: hello world!, welcome to the online tutorial

Example 2 - Title Case and Simple Conversions

<?php
    $string = "hello world!, welcome to the online tutorial";

    // Convert to title case
    $title = mb_convert_case($string, MB_CASE_TITLE, "UTF-8");
    echo "Title Case: " . $title . "<br>";

    // Simple uppercase conversion (PHP 7.3+)
    $upperSimple = mb_convert_case($string, MB_CASE_UPPER_SIMPLE, "UTF-8");
    echo "Upper Simple: " . $upperSimple . "<br>";
?>

Title Case: Hello World!, Welcome To The Online Tutorial
Upper Simple: HELLO WORLD!, WELCOME TO THE ONLINE TUTORIAL

Conclusion

The mb_convert_case() function provides robust case conversion for multibyte strings. Use appropriate mode constants based on your needs and always specify encoding for consistent results across different character sets.