C++ exeption sample

exeption.cc

#include <iostream>
#include <stdexcept>

using namespace std;

class my_exception_t : public exception
{
        const char * str;
        public:
        int data = 10;
        int test2(){
                return data;
        }
        explicit my_exception_t(char * c){
                str = c; 
        }

        virtual const char* what() const throw() {
                return "Hello, world!"; 
        }

        const char * hello() throw(){
                return "hello";
        }
        const char * test() throw(){
                return str;
        }
};

int main()
{
        my_exception_t ex = my_exception_t("test: ");
        ex.data = 20;
        ex.test2();
        try {
                throw ex;
        } catch (my_exception_t& error){
                cerr << "Exception: " << error.what() << endl;
                cerr << error.hello() << endl;
                cerr << error.test() << error.data << endl;
        } catch (exception& error){
                cerr << "Exception: " << error.what() << endl;
        } catch (...) {
                cerr << "Exception: unknown" << endl;
        }

        return 0;
}