sharedptr2.cpp

/*
	Author: Raúl Roa
	
	Description
	-----------
	This program is meant to demonstrate how shared pointers allow for transfer of ownership.
	Two lists contain a reference to the same pointer; remove operations are applied separately 
	and data integrity remains.
	
	References
	-----------
	std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer.
	http://en.cppreference.com/w/cpp/memory/shared_ptr
*/

#include <iostream>
#include <memory>
#include <list>
#include <cassert>
#include <algorithm>

#define SINGLE_REF 0

struct Bar;
struct Foo;

std::list<std::shared_ptr<Bar>> bars;
std::list<std::shared_ptr<Foo>> foos;

struct Bar
{	
	~Bar() { std::cout << "Bar desct!\n"; }
	void sayHi() { std::cout << "Hi Bar\n"; }
};

struct Foo : Bar
{
	void sayHi() { std::cout << "Hi Foo\n"; }
};

void Init()
{
	std::shared_ptr<Foo> ptr(new Foo);
	bars.push_back(ptr);
	foos.push_back(ptr);
}

void Cleanup()
{	
	#if SINGLE_REF
		bars.clear();
	#else
		for (std::list <std::shared_ptr<Bar>>::iterator iter = bars.begin(); iter != bars.end(); ++iter)
		{
			bars.remove((*iter));
			break;
		}
	#endif
}

int main()
{				
	Init();
	Cleanup();

	#if !SINGLE_REF
		for (std::list <std::shared_ptr<Foo>>::iterator iter = foos.begin(); iter != foos.end(); ++iter)
		{
			(*iter)->sayHi();
		}
		assert(foos.size() == 1);
	#endif
	
	assert(bars.size() == 0);

	std::cout << "Bars: " << bars.size() << std::endl;
	std::cout << "Foos: " << foos.size() << std::endl;

	std::cin.get();

	return 0;
}