substr of chinese charactor error ?/b>

[queensumiv]

Any one know about using substr($chinesechar,0,4) when the
$chinesechar="123Äã";

It comes out the error ? symbol when under :

<b><?echo $chinesechar?></b>

the error was: 123?/b>

Trying to use the mb_substr but don't know why it said no such function in my php 4.3.3 under window 2k.

Try tested the ? with a "?", but no match, may be the php don't like me recently as I use it very very often lately.

Any one knows an answer to test this ? symbols or error code.