mb_strtolower

Function name: mb_strtolower()

Applicable version: PHP 4 >= 4.3.0, PHP 5, PHP 7

Usage: mb_strtolower(string $str, string|null $encoding = null): string

Function Description: The mb_strtolower() function converts all characters in a string to lowercase. The difference between this function and the strtolower() function is that it correctly handles non-ASCII characters and multi-byte characters.

parameter:

• $str (required): A string to be converted to lowercase.
• $encoding (optional): The character encoding to use. If not specified, internal character encoding is used.

Return value: Returns a string converted to lowercase.

Example:

 $str = "HELLO WORLD!"; $lowercase = mb_strtolower($str); echo $lowercase; // 输出：hello world! $str = "你好，世界！"; $lowercase = mb_strtolower($str, "UTF-8"); echo $lowercase; // 输出：你好，世界！（由于中文字符没有大小写之分，所以不会改变）

In the example above, we first convert the string "HELLO WORLD!" to lowercase using the mb_strtolower() function and store the result in the variable $lowercase. Then, we use the echo statement to output the result to the screen, with the output as "hello world!".

In the second example, we use the mb_strtolower() function to convert the string "Hello, World!" containing Chinese characters to lowercase. Since Chinese characters do not have a case distinction, the result is the same as the original string. Note that we also specified the character encoding as "UTF-8" to ensure that multibyte characters are processed correctly.