shared

读陈硕书《Linux多线程服务端编程》，有一句话不能理解：析构在创建时被捕获，这意味着虚析构不再是必须的。实际代码操作了一下，发现确实通过shared_ptr去释放派生类对象，无需将析构函数置为virtual，代码如下：

#include <iostream> #include <memory> using namespace std; class base { public: base(){cout << "base construct" << endl;} virtual void print(){cout << "base print" << endl;} ~base(){cout << "base destruct" << endl;} }; class derived: public base { public: derived(){cout << "derived construct " << endl;} void print(){cout << "derived print" << endl;} ~derived(){cout << "derived destruct" << endl;} }; int main() { shared_ptr<base> ptr(new derived()); return 0; }

代码打印为：

base construct derived construct derived destruct base destruct

而后阅读文章[c++ 笔记]shared_ptr 理解创建时即捕获析构动作，感觉该文章给出了一个较为合理的解释，不过模拟shared_ptr原理的代码编译不过，这边稍作修改

#include <iostream> template <typename T> class simple_ptr_internal_interface { public: virtual T* get() = 0; virtual void destruct() = 0; }; // class simple_ptr_internal_interface template <typename T, typename D> class simple_ptr_internal: public simple_ptr_internal_interface<T> { public: struct DefaultDeleter { void operator()(T* t) { delete static_cast<D*>(t); } }; simple_ptr_internal(T* p): pointer(p) {} virtual T* get() override { return pointer; } virtual void destruct() override { deleter(pointer); } private: T* pointer; DefaultDeleter deleter; }; // class simple_ptr_internal template <typename T> class simple_ptr { public: template <typename Derived> simple_ptr(Derived* d): internal(new simple_ptr_internal<T, Derived>{d}) {} ~simple_ptr() { this->destruct(); } private: void destruct() { internal->destruct(); } simple_ptr_internal_interface<T>* internal; }; class base { public: base(){std::cout << "base construct" << std::endl;} ~base(){std::cout << "base destruct" << std::endl;} }; class derived: public base { public: derived(){std::cout << "derived construct " << std::endl;} ~derived(){std::cout << "derived destruct" << std::endl;} }; int main() { simple_ptr<base>(new derived()); return 0; }

代码打印为：

base construct derived construct derived destruct base destruct