mbinternalencoding

mb_internal_encoding is a function in PHP’s mbstring extension that gets or sets the internal character encoding used by multibyte string functions. It determines the default encoding for mbstring functions that do not receive an explicit encoding parameter, such as mb_strlen, mb_substr, and mb_strpos. The function is commonly referenced as mb_internal_encoding() in documentation.

When called without arguments, it returns the current internal encoding as a string. When called with a string argument specifying an encoding (for example 'UTF-8'), it sets the internal encoding to that value and returns the previous encoding. This change affects subsequent calls to many mbstring functions that rely on the internal encoding.

The internal encoding can be configured via the mbstring.internal_encoding directive in php.ini, or at runtime with mb_internal_encoding(). Common values include 'UTF-8' and legacy encodings such as 'ISO-8859-1' or 'Shift_JIS'. It is generally recommended to use UTF-8 for modern applications to maximize compatibility and avoid multibyte parsing issues.

Note that mb_internal_encoding() requires the mbstring extension. If mbstring is not loaded, the function is unavailable and multibyte-aware functions may default to byte-oriented behavior. When dealing with unknown input, mb_detect_encoding can help determine a suitable encoding before processing.

Example: $enc = mb_internal_encoding(); mb_internal_encoding('UTF-8'); // now mbstring functions use UTF-8 by default. See also mb_detect_encoding and mbstring.