C++ - 智能指针(smarter pointer)自定义删除器(deleter) 的方法 详解 及 代码

智能指针(smarter pointer)自定义删除器(deleter) 的方法 详解 及 代码

 

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智能指针包含两种"shared_ptr"和"unique_ptr", 由于两种指针的实现方式不同, 所以传递删除器的方式也不同;

"shared_ptr"的传递删除器(deleter)方式比较简单, 只需要在参数中添加具体的删除器函数名, 即可; 注意是单参数函数;

"unique_ptr"的删除器是函数模板(function template), 所以需要在模板类型传递删除器的类型(即函数指针(function pointer)), 再在参数中添加具体删除器;

定义函数指针的类型, 包含三种方法(typedef, typedef decltype, using), 也可以直接传递decltype;

参考注释, 具体代码如下:

/*   * cppprimer.cpp   *   *  Created on: 2013.11.24   *      Author: Caroline   */    /*eclipse cdt, gcc 4.8.1*/    #include <iostream>  #include <memory>    using namespace std;    void deleter (int* ptr) {  	delete ptr;  	ptr = nullptr;  	std::clog << "shared_ptr delete the pointer." << std::endl;  }    int main (void) {    	//定义函数类型  	typedef void (*tp) (int*);  	typedef decltype (deleter)* dp;  	using up = void (*) (int*);    	std::shared_ptr<int> spi(new int(10), deleter);  	std::shared_ptr<int> spi2(new int, deleter);  	spi2 = std::make_shared<int>(15);    	std::cout << "*spi = " << *spi << std::endl;  	std::cout << "*spi2 = " << *spi2 << std::endl;    	//unique_ptr是模板函数需要删除器(deleter)类型, 再传入具体的删除器  	std::unique_ptr<int, decltype(deleter)*> upi(new int(20), deleter);  	std::unique_ptr<int, tp> upi2(new int(25), deleter);  	std::unique_ptr<int, dp> upi3(new int(30), deleter);  	std::unique_ptr<int, up> upi4(new int(35), deleter);    	std::cout << "*upi = " << *upi << std::endl;  	std::cout << "*upi2 = " << *upi2 << std::endl;  	std::cout << "*upi3 = " << *upi3 << std::endl;  	std::cout << "*upi4 = " << *upi4 << std::endl;    	return 0;    }  

输出:

shared_ptr delete the pointer.  shared_ptr delete the pointer.  shared_ptr delete the pointer.  shared_ptr delete the pointer.  shared_ptr delete the pointer.  shared_ptr delete the pointer.  *spi = 10  *spi2 = 15  *upi = 20  *upi2 = 25  *upi3 = 30  *upi4 = 35