CODEWITHSUNDEEP
c++c++11overriding
Masahiro
Masahiro

Reputation: 175

How to identify the vector classes which override from different child classes?

I would like to identify which child classes initialize pointers in a vector.

I prepare a vector that contains different types of override classes. After that, I set it as an argument in the same function. In the function, I would like to identify which classes initialize this argument and apply different processes for each class.

This is the code and current output.

#include <memory>
#include <iostream>
#include <vector>

class Parent
{
public:
    Parent() {};
    virtual ~Parent() {};

    virtual void print() 
    {
        std::cout << "I am parent!" << std::endl;
    }

};


class ChildA : public Parent
{
public:
    ChildA() {};
    ~ChildA() {};

    void print() override
    {
        std::cout << "I am child A!" << std::endl;
    }

};

class ChildB : public Parent
{
public:
    ChildB() {};
    ~ChildB() {};

    void print() override
    {
        std::cout << "I am child B!" << std::endl;
    }
};

void func(std::unique_ptr<Parent>& pa)
{
    pa->print();

    //if (pa is initialized from Parent)
    //{
    //}

    //if (pa is initialized from ChildA)
    //{
    //}

    //if (pa is initialized from ChildB)
    //{ 
    //}

    return;
}

int main(int argc, char** argv)
{
    std::unique_ptr<Parent> pa = std::make_unique<Parent>();
    std::unique_ptr<ChildA> chA = std::make_unique<ChildA>();
    std::unique_ptr<ChildB> chB = std::make_unique<ChildB>();


    std::vector<std::unique_ptr<Parent>> mList;
    mList.push_back(std::move(pa));
    mList.push_back(std::move(chA));
    mList.push_back(std::move(chB));

    for (auto& l : mList)
        func(l);

    return 0;
}

output 

I am parent!
I am child A!
I am child B!

Could you tell me any idea? Thank you.

Upvotes: 0

Views: 54

Answers (1)

Anthony Williams
Anthony Williams

Reputation: 68561

The purpose of doing polymorphic code with virtual functions is usually so you can avoid doing "is this an X" style tests. Instead you create a virtual function doSpecialStuff in the base class and call it via a base class pointer (like print in your code), which then does the appropriate operations for each derived class.

If you really want to test the type, use dynamic_cast:

if(auto child_ptr=dynamic_cast<ChildA*>(pa.get())){
   child_ptr->child_A_function();
}

Upvotes: 1

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