#include <iostream>

class problem
{
public:
    problem(int val) : m_val(val) { }

    virtual void debug()
    {
        std::cout << "debug problem" << std::endl;
    }

    void trace()
    {
        std::cout << "val: " << m_val << std::endl;
    }

private:
    int m_val;
};

class subproblem : public problem
{
public:
    subproblem(int val) : problem(val) {}

    virtual void debug()
    {
        std::cout << "debug subproblem" << std::endl;
    }
};

int main()
{
    problem* proml = nullptr;
    try {
        proml->debug();
    }
    catch(...) {
        std::cout << "bad call" << std::endl;
    }
    return 0;
}