Defined (2)

The function is defined in the following location(s).

/wp-includes/compat.php  

function mb_strlen( $str, $encoding = null ) { 
    return _mb_strlen( $str, $encoding ); 
} 

function _mb_strlen( $str, $encoding = null ) { 
    if ( null === $encoding ) { 
        $encoding = get_option( 'blog_charset' ); 
    } 
 
    /** 
     * The solution below works only for UTF-8, so in case of a different charset 
     * just use built-in strlen(). 
     */ 
    if ( ! in_array( $encoding, array( 'utf8', 'utf-8', 'UTF8', 'UTF-8' ) ) ) { 
        return strlen( $str ); 
    } 
 
    if ( _wp_can_use_pcre_u() ) { 
        // Use the regex unicode support to separate the UTF-8 characters into an array. 
        preg_match_all( '/./us', $str, $match ); 
        return count( $match[0] ); 
    } 
 
    $regex = '/(?: 
          [\x00-\x7F]                  # single-byte sequences   0xxxxxxx 
        | [\xC2-\xDF][\x80-\xBF]       # double-byte sequences   110xxxxx 10xxxxxx 
        | \xE0[\xA0-\xBF][\x80-\xBF]   # triple-byte sequences   1110xxxx 10xxxxxx * 2 
        | [\xE1-\xEC][\x80-\xBF]{2} 
        | \xED[\x80-\x9F][\x80-\xBF] 
        | [\xEE-\xEF][\x80-\xBF]{2} 
        | \xF0[\x90-\xBF][\x80-\xBF]{2} # four-byte sequences   11110xxx 10xxxxxx * 3 
        | [\xF1-\xF3][\x80-\xBF]{3} 
        | \xF4[\x80-\x8F][\x80-\xBF]{2} 
 )/x'; 
 
    // Start at 1 instead of 0 since the first thing we do is decrement. 
    $count = 1; 
    do { 
        // We had some string left over from the last round, but we counted it in that last round. 
        $count--; 
 
        /** 
         * Split by UTF-8 character, limit to 1000 characters (last array element will contain 
         * the rest of the string). 
         */ 
        $pieces = preg_split( $regex, $str, 1000 ); 
 
        // Increment. 
        $count += count( $pieces ); 
 
    // If there's anything left over, repeat the loop. 
    } while ( $str = array_pop( $pieces ) ); 
 
    // Fencepost: preg_split() always returns one extra item in the array. 
    return --$count; 
}