Question

My question is this: why does the following code:

class A
{
public:
    A()
    {
        test[0] = "three";
        test[5] = "five";
        test2[3] = 5.55;
    }
    void foo(int j)
    {
        for(int i = j+1; i <= 7; ++i)
        {
            try
            {
                std::cout<<test.at(i)<<"\n";
            }
            catch(const std::out_of_range&)
            {
                try
                {
                    std::cout<<test2.at(i)<<"\n";
                }
                catch(const std::out_of_range&)
                {
                    throw i;
                }
            }
        }
    }
    virtual void bar()
    {

    }
    std::map< int, float > test2;
    std::map<int, std::string> test;
};

class B : public A
{
public:
    B()
    {
        test3[6] = 15;
        test3[7] = 42;
        bar();
    }

    void bar()
    {
        int k = -1;
        label:
        try
        {
            foo(k);
        }
        catch(int i)
        {
            try
            {
                std::cout<<test3.at(i)<<"\n";
            }
            catch(const std::out_of_range&)
            {
                k = i;
                goto label;
            }
        }
    }

std::map<int, int> test3;
};

print

three
5.55
five
15

and not

three
5.55
five
15
42

?

What I’m trying to do is iterate over a number of maps containing different data types that can’t be held in 1 container and this is what I came up with

Answer 1

My understanding is that what you need is:

• You want to print all values contained in different maps over a certain range of keys.
• The maps have different types of values. Not all keys are present in all maps.
• A derived class may contain additional maps.

Instead of this convoluted exception+goto design, why not use a simpler design based on a virtual method for printing a specific value:

class A {
public:
    virtual void showValue(int key) {
        if (map1.count(key))
            std::cout << map1[key];
        else if (map2.count(key))
            std::cout << map2[key];
    }

    void showAll() {
        for (int i=0; i<=7; i++)
            showValue(i);
    }

    std::map<int, float> map1;
    std::map<int, std::string> map2;
};

class B : public A {
public:
    virtual void showValue(int key) {
        if (map3.count(key))
            std::cout << map3[key];
        else
            A::showValue(key);
    }

    std::map<int, int> map3;
};