Can php detect 4-byte encoded utf8 chars?

Question

I am using a utf8 charset mysql tables in a mysql 5.1 server, which does not support utf8mb4 encoding in tables. When inserting 4-byte encoded utf8 characters like \"

Answer 1

The following regular expression will replace 4-byte UTF-8 characters:

function replace4byte($string, $replacement = '') {
    return preg_replace('%(?:
          \xF0[\x90-\xBF][\x80-\xBF]{2}      # planes 1-3
        | [\xF1-\xF3][\x80-\xBF]{3}          # planes 4-15
        | \xF4[\x80-\x8F][\x80-\xBF]{2}      # plane 16
    )%xs', $replacement, $string);    
}

var_dump(replace4byte('d'), replace4byte('d