error: invalid conversion from 'const XMLCh* {aka const short unsigned int*}' to 'XMLCh* {aka short unsigned int*}' [-fpermissive]
 #define X(str) XStr(str).unicodeForm()
                                      ^
------------------------
using namespace xercesc;
using namespace std;

class XStr
{
public :
    XStr(const char* const toTranscode)
    {
        // Call the private transcoding method
        fUnicodeForm = XMLString::transcode(toTranscode);
    }

    ~XStr()
    {
        XMLString::release(&fUnicodeForm);
    }

    const XMLCh* unicodeForm() const
    {
        return fUnicodeForm;
    }

private :
    XMLCh*   fUnicodeForm;
};

#define X(str) XStr(str).unicodeForm()