Advertisement Jump to content
Sign in to follow this  
BaneTrapper

Making a copy of object from a pointer but dont know its type

This topic is 1737 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hello.

In the main where i make a copy of above objects(bellow that comment) i don't know how to determinate what type the object it is so i wrote (a) for this example

[code]
class a
{
public:
    virtual void Print();
};

class b : public a
{
public:
    void Print();
};

class c : public a
{
public:
    void Print();
};
//////////////////////////////////////////
void a::Print()
{
    std::cout<<"a"<<std::endl;
}
void b::Print()
{
    std::cout<<"b"<<std::endl;
}
void c::Print()
{
    std::cout<<"c"<<std::endl;
}
//////////////////////////////////////////
int main()
{
    std::unique_ptr<a> objA1 = std::unique_ptr<a>(new b);
    std::unique_ptr<a> objA2 = std::unique_ptr<a>(new c);
    //Make a copy of above objects
    std::unique_ptr<a> objA3 = std::unique_ptr<a>(new a/*this a i do not know to to determinate its type*/(*objA1));
    std::unique_ptr<a> objA4 = std::unique_ptr<a>(new a/*also this a i do not know to to determinate*/(*objA2));

    objA1->Print();
    objA2->Print();
    objA3->Print();
    objA4->Print();

    system("pause");
    return 0;
};
[/code]

Output is

b
c
a
a

But i need it to be (b c b c) how can i achieve that?

Share this post


Link to post
Share on other sites
Advertisement
The general solution is to add a 'virtual a* clone() const' function and require that every subclass implements it correctly.

Share this post


Link to post
Share on other sites

You can even automate the process of defining the clone-methods by adding a intermedia templated class:

class a
{
public:

	virtual a* Clone(void) = 0;
	virtual void Print();
}

template<typename Class>
class a1 : public a
{
public:

	a* Clone(void) const override final
	{
		return new Class(*this);
	}
}

class b : public a1<b>
{
public:

	void Print();
}

class c : public a1<c>
{
public:

	void Print();
}

This can be usefull in reducing redundant code, since many/all implementations of clone will probably just call the classes copy-ctor in the first place, specially if you have many classes that derive from "a".

Share this post


Link to post
Share on other sites

Ive bean reading true changes in c++11 and i think i will change the design not to use polymorphism in this part, thanks on help anywai.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

GameDev.net is your game development community. Create an account for your GameDev Portfolio and participate in the largest developer community in the games industry.

Sign me up!