utf8mb4 - 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 "??","??","??","??","??","唧","??". The table will popup error or skip the following texts.

How can I programmatically detect 4-byte encoded utf8 characters in PHP and replace them?

Answer 1

This should work:

if (max(array_map('ord', str_split($string))) >= 240) 

The rational being that code points up to and including U+FFFF are encoded as three bytes of the form 1110xxxx 10xxxxxx 10xxxxxx. Higher code points are of the form 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx, i.e. the highest byte has a value of 240 or higher. If there are any such bytes in the string, it's an indicator for a 4-byte sequence.

If you want to remove long characters, this will do:

preg_replace_callback('/./u', function (array $match) {
    return strlen($match[0]) >= 4 ? null : $match[0];
}, $string)

Though there may be a more elegant regex way to express high codepoints directly.