mbstrtolower

mb_strtolower is a PHP function provided by the mbstring extension that converts a string to lowercase in a multibyte-aware manner. It is designed to correctly handle non-ASCII characters by using the specified encoding’s case mappings, making it suitable for international text.

Syntax and parameters

The function signature is mb_strtolower(string $str [, string $encoding = mb_internal_encoding()]). The default encoding is the value returned by mb_internal_encoding(). The first argument $str is the input string. The optional $encoding parameter selects the character encoding to apply when determining lowercase mappings, with common choices including UTF-8, ISO-8859-1, and EUC-JP. The function is encoding-aware rather than locale-based.

Return value and behavior

mb_strtolower returns a string in which all alphabetic characters have been converted to lowercase according to the specified encoding. Characters without a lowercase mapping or that are not letters remain unchanged. If the encoding is unsupported or an error occurs, the function returns false.

Notes and context

mb_strtolower is part of the mbstring extension and requires it to be enabled in the PHP installation. It is multibyte-safe and commonly used to normalize text for comparisons, storage, or display. It differs from the non-multibyte strtolower function in that it correctly handles multibyte character sets rather than relying on locale-dependent behavior.

See also

mb_strtoupper, mb_convert_case, and related mbstring functions for case conversion and encoding handling.