play_with_shared_ptr.cpp

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

class Base
{
public:
   virtual void print(){}	
};

class ChildA : public Base
{
public:
	void print() override
	{
		std::cout << "ChildA::print() shows x=" << x << std::endl;
	}
	int x = 0;
};

class ChildB : public Base
{
public:
	void print() override
	{
		std::cout << "ChildB::print() shows y=" << y << std::endl;
	}
	int y = 10;
};

void accessChildProperties(std::shared_ptr<Base> basePtr)
{
	std::shared_ptr<ChildA> childA = std::dynamic_pointer_cast<ChildA>(basePtr); 
	if(childA != nullptr)
	{
		std::cout<< "successfully cast to ChildA. Num refs = " << childA.use_count() << ". Retrieved value of x = " << childA->x << std::endl;
	}
	std::shared_ptr<ChildB> childB = std::dynamic_pointer_cast<ChildB>(basePtr); 
	if(childB != nullptr)
	{
		std::cout<< "successfully cast to ChildB. Num refs = " << childB.use_count() << ". Retrieved value of y = " << childB->y << std::endl;
	}
}

int main()
{
	std::vector<std::shared_ptr<Base>> vec;
	vec.push_back(std::make_shared<ChildA>());
	vec.push_back(std::make_shared<ChildB>());
	vec.push_back(std::make_shared<ChildB>());
	vec.push_back(std::make_shared<ChildB>());
	vec.push_back(std::make_shared<ChildB>());
	vec.push_back(std::make_shared<ChildB>());
	std::shared_ptr<Base> childA_ptr  = *(vec.begin());	
	for(auto it = vec.begin(); it != vec.end(); ++it)
	{
		(*it)->print();
		accessChildProperties(*it);
	}
	std::cout << "Num references to child a = " << childA_ptr.use_count() << std::endl;
	vec.erase(vec.begin());
	vec.erase(vec.begin());
	vec.erase(vec.begin());
	vec.erase(vec.begin());
	vec.erase(vec.begin());
	vec.erase(vec.begin());
	std::cout << "Num references to child a after erasing vector contents = " << childA_ptr.use_count() << std::endl;
	childA_ptr.reset();
	std::cout << "Num references to child a after reset = " << childA_ptr.use_count() << std::endl;
}