[xslt] Abt Libxslt use in replace function

[bhushan <sonawanebhushan gmail com>]

i have written code which will convert XML file to some other format 
in this conversion i want to read some nodes data character by character 
so i hv used fn:replace function with this name space
   xmlns:fn="
http://www.w3.org/2005/xpath-functions" (added line in header)
 & use replace function of 
fn namespace .
       when i compile code it says 

xmlXPathCompOpEval: function replace not found
XPath error : Unregistered function
xmlXPathCompOpEval: function date not found
XPath error : Unregistered function

 so how to register this function .
 i am using 1.1.17 version of libxslt 

Plz Plz help me out of this 

Regards 
-- bhushan. E . Sonawane