unique_ptr的大小探讨

unique_ptr大小和删除器有很大关系，具体区别看如下代码的分析。不要让unique_ptr占用的空间太大，否则不会达到裸指针同样的效果。

#include <iostream>
#include <memory>
using namespace std;

class Widget {
    
    
	int m_x;
	int m_y;
	int m_z;

public:
	Widget(int x, int y, int z) :
		m_x(x), m_y(y), m_z(z)
	{
    
    }

	void print() {
    
    
		cout << m_x << "," << m_y << "," << m_z << endl;
	}

	~Widget()
	{
    
    
		cout << "Widget dtor" << endl;
	}
};


struct DeleteWithLog {
    
    
	void operator()(Widget* w) {
    
    
		data++;
		delete w;
		cout << "------ DeleteWithLog delete w" << endl;
	}

	int data;
};

void deleteFunction(Widget* w) {
    
    
	delete w;
	cout << "------ deleteFunction delete w" << endl;
}


int main()
{
    
    
	{
    
    

		unique_ptr<Widget> w1(new Widget(1, 2, 3));
		w1->print();
		cout <<"sizeof(w1) = " <<sizeof(w1) << endl;
		cout << "------ default delete" << endl;
	}

	{
    
    
		DeleteWithLog dw;
		unique_ptr<Widget, DeleteWithLog> w2(new Widget(10, 20, 30));
		w2->print();
		cout << "sizeof(w2) = " << sizeof(w2) << endl;
	}
	
	int data1, data2, data3;
	{
    
    
		auto lambda = [=](Widget * w) {
    
    
			cout << data1 << data2 << data3 << endl;
			delete w;
			cout << "------ lambda delete w" << endl;
		};
		unique_ptr<Widget, decltype(lambda)> w3(new Widget(100, 200, 300), lambda);
		w3->print();
		cout << "sizeof(w3) = " << sizeof(w3) << endl;
	}

	{
    
    
		unique_ptr<Widget, void(*)(Widget*)>
			w4(new Widget(1000, 2000, 3000), deleteFunction);
		w4->print();
		cout << "sizeof(w4) = " << sizeof(w4) << endl;
	}


	system("pause");
}

结果：