title: Can php detect 4-byte encoded utf8 chars?
body: <p>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 <code>"","","","","","唧",""</code>. The table will popup error or skip the following texts.</p>
  
  <p>How can I programmatically detect  4-byte encoded utf8 characters in PHP and replace them?</p>