when i run VC for printing my own dom example, i encounter a runtime virtual function call error.

what i do is as following:

Inherit my own class MyXMLFormatTarget from XMLFormatTarget
then add a function :
 
 void writeChars(const char* const toWrite,
     const unsigned int count,
                    XMLFormatter* const formatter
 );

for there is only a similar function 

 void writeChars
    (
        const   XMLByte* const  toWrite
        , const unsigned int    count
        , XMLFormatter* const   formatter
    );

in which the first argument is XMLByte*, does not support my dom model.
In such way, it does work, but when it prints all the document, there is a runtime error
saying a virtual function is called, i do not know why.