Mine

                class LexError : public std::exception
                {
                        unsigned int myLineNumber;
                        public:
                                LexError(const unsigned int lineNumber) :
                                        myLineNumber(lineNumber) {};
                                virtual const char* what() const throw()
                                {
                                        std::string errorMessage;
                                        std::stringstream ss(std::stringstream::in
                                        | std::stringstream::out);

                                        ss << "Line " << (char *)lineNumber << ": General Error";

                                        errorMessage = ss.str();
                                        return errorMessage.c_str();
                                }
                                ~LexError() throw() {};
                };