C++11补充：智能指针如std::unique_ptr如何添加自定义的deleter

关于智能指针的问题，有时候为了方便，需要在析构时附加一些清理操作，或者，有的指针本身来自C的库文件中，这时候，就非常期望能够使用自定义的deleter，

但是标准C++创建函数如std::make_unique / std::make_shared 等不支持创建带有自定义deleter的智能指针，这时，我们只能使用自己的办法，

cpp 复制代码

#include <memory>
#include <iostream>

class myclass {
public:
	myclass() {
		std::cout << "myclass" << std::endl;
	}

	~myclass() {
		std::cout << "~myclass" << std::endl;
	}

	void doSomething() {
		std::cout << "myclass is doing something" << std::endl;
	}
};

class A {
public:
	A(){
		std::cout << "A" << std::endl;
	}

	~A(){
		std::cout << "~A" << std::endl;
	}

	void doSomething() {
		std::cout << "A is doing something" << std::endl;
	}
};

struct my_creator_s {
	myclass* p = new myclass();
	A* a = new A();
};
struct my_deleter_s {
	void operator()(myclass* p) { delete p; }

};
struct my_deleter_s2 {
	void operator()(my_creator_s* s) { delete s->p; delete s->a; }
};

myclass* mycreator() {
	return new myclass();
}
void mydeleter(myclass* p){
	delete p;
};

int Test1() {
	std::cout << "----------------------------Test Method 1-----------------------------" << std::endl;
	myclass* myptr = new myclass;
	std::unique_ptr<myclass, decltype(&mydeleter)> ptr{ myptr,  &mydeleter };
	ptr->doSomething();
	return 0;
}

int Test2() {
	std::cout << "----------------------------Test Method 2-----------------------------" << std::endl;
	std::unique_ptr<myclass, my_deleter_s> ptr2 = std::unique_ptr<myclass, my_deleter_s>(new myclass(), my_deleter_s());
	ptr2.get()->doSomething();
	return 0;
}

int Test3() {
	std::cout << "----------------------------Test Method 3-----------------------------" << std::endl;
	std::unique_ptr<my_creator_s, my_deleter_s2> ptr3 = std::unique_ptr<my_creator_s, my_deleter_s2>(new my_creator_s(), my_deleter_s2());
	ptr3.get()->a->doSomething();
	return 0;
}

int main() {
	Test1();
	Test2();
	Test3();
	return 0;
}

这段代码的输出如下，

----------------------------Test Method 1-----------------------------

myclass

myclass is doing something

~myclass

----------------------------Test Method 2-----------------------------

myclass

myclass is doing something

~myclass

----------------------------Test Method 3-----------------------------

myclass

A is doing something

~myclass

说明：这里写了两个creator，函数mycreator没有用到；deleter一个采用了struct的办法，一个是采用了void函数的办法，大家可以自己尝试；对于需要同时处理多个参数或变量的形式，建议采用struct或class的形式，Test Ｍethod3展示了如何使用creator或者说constructor创建的办法，写成这种方式是因为智能指针的deleter中只接受一个参数，例如，不能写成这样的，

cpp 复制代码

struct my_deleter_s2 {
	void operator()(myclass* p, A* a) { delete p; delete a; }
};

参考附录：

Custom Deleter for C++ Smart Pointers - Lei Mao's Log Book

本文结束