[xml] How xmlXPathEvalExpression() eval CHINESE xpath expression?

[canbaby <canbaby 21cn com>]

Hello:
   help me, How could I  use xmlXPathEvalExpression()  to eval a xpath 
that contain CHINESE?
I test it, but error message:
   xpath error: encoding error
I thinks it's the problem encoding, but I'm a newbie, so want your help.
give some code better

   thanks