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UniquePtr_SmartPointer.cpp
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UniquePtr_SmartPointer.cpp
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/**
* Demonstrate usage of std::unique_ptr smart pointer.
*
* This program uses std::make_unique which is available since c++14.
* Compile it with `g++ -std=c++14 ...`.
*/
#include <iostream>
#include <memory>
#include <vector>
#include <algorithm>
class Widget
{
public:
Widget(): a(0)
{
std::cout << "Widget - ctor1" << std::endl;
}
Widget(const int a): a(a)
{
std::cout << "Widget - ctor2" << std::endl;
}
~Widget()
{
std::cout << "Widget - dtor(" << a << ")" << std::endl;
}
const int GetA() const
{
return a;
}
void SetA(const int a)
{
this->a = a;
}
private:
int a;
};
int main()
{
std::cout << "sizeof(std::unique_ptr<Widget>) = " << sizeof(std::unique_ptr<Widget>) << std::endl;
// support both single or array of objects as managed objects
std::unique_ptr<Widget> u1( new Widget(1) );
std::unique_ptr<Widget[]> u2( new Widget[5] );
Widget* w = new Widget(3);
std::unique_ptr<Widget> u3( w );
std::cout << w->GetA() << std::endl;
std::cout << u3->GetA() << std::endl;
u3.reset();
// should not call any methods from managed object, or smart pointer again
//std::cout << w->GetA() << std::endl;
//std::cout << u3->GetA() << std::endl;
// access element in array of objects of unique_ptr
u2[0].SetA(0);
u2[1].SetA(1);
u2[2].SetA(2);
u2[3].SetA(3);
u2[4].SetA(4);
for (int i=0; i<5; ++i)
{
std::cout << "u2[" << i << "] = " << u2[i].GetA() << std::endl;
}
// move (to transfer ownership)
std::unique_ptr<Widget> u4 = std::move(u1);
if (u4.get() == nullptr)
{
std::cout << "u4.get() is nullptr" << std::endl;
}
if (u1.get() == nullptr)
{
std::cout << "u1.get() is nullptr" << std::endl;
}
// move (of array of objects type, to transfer ownership)
std::unique_ptr<Widget[]> u5 = std::move(u2);
std::cout << "u5[4] = " << u5[4].GetA() << std::endl;
if (u2.get() == nullptr)
{
std::cout << "u2.get() is nullptr" << std::endl;
}
// use std::make_unique
// note: available only since C++14
std::unique_ptr<Widget> u6 = std::make_unique<Widget>(6);
return 0;
}