模板学习实践二 pointer

c++ template学习记录

使用模板将实际类型的指针进行封装

当变量退出作用域 自动delete

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// 1111.cpp : 定义控制台应用程序的入口点。 //   #include "stdafx.h"   template <typename T> class Holder { private:     T* ptr;    // refers to the object it holds (if any)   public:     // default constructor: let the holder refer to nothing     Holder() : ptr(0) {     }       // constructor for a pointer: let the holder refer to where the pointer refers     explicit Holder(T* p) : ptr(p) {     }       // destructor: releases the object to which it refers (if any)     ~Holder() {         delete ptr;     }       // assignment of new pointer     Holder<T>& operator= (T* p) {         delete ptr;         ptr = p;         return *this;     }       // pointer operators     T& operator* () const {         return *ptr;     }       T* operator-> () const {         return ptr;     }       // get referenced object (if any)     T* get() const {         return ptr;     }       // release ownership of referenced object     void release() {         ptr = 0;     }       // exchange ownership with other holder     void exchange_with(Holder<T>& h) {         std::swap(ptr, h.ptr);     }       // exchange ownership with other pointer     void exchange_with(T*& p) {         std::swap(ptr, p);     }   private:     // no copying and copy assignment allowed     Holder(Holder<T> const&);     Holder<T>& operator= (Holder<T> const&); };   class Something { public:     void perform() const {     } };   void do_two_things() {     Holder<Something> first(new Something);     first->perform();       Holder<Something> second(new Something);     second->perform(); }   int main() {     do_two_things(); }

　　

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// 1111111.cpp : 定义控制台应用程序的入口点。 //   #include "stdafx.h" #include <stddef.h> #include <iostream> #include <vector>   using namespace std;   size_t* alloc_counter() {     return ::new size_t; }   void dealloc_counter(size_t* ptr) {     ::delete ptr; }   class SimpleReferenceCount { private:     size_t* counter;    // the allocated counter public:     SimpleReferenceCount() {         counter = NULL;     }       // default copy constructor and copy-assignment operator     // are fine in that they just copy the shared counter   public:     // allocate the counter and initialize its value to one:     template<typename T> void init(T*) {         counter = alloc_counter();         *counter = 1;     }       // dispose of the counter:     template<typename T> void dispose(T*) {         dealloc_counter(counter);     }       // increment by one:     template<typename T> void increment(T*) {         ++*counter;     }       // decrement by one:     template<typename T> void decrement(T*) {         --*counter;     }       // test for zero:     template<typename T> bool is_zero(T*) {         return *counter == 0;     } };   class StandardArrayPolicy { public:     template<typename T> void dispose(T* array) {         delete[] array;     } };   class StandardObjectPolicy { public:     template<typename T> void dispose(T* object) {         delete object;     } };   template<typename T,     typename CounterPolicy = SimpleReferenceCount,     typename ObjectPolicy = StandardObjectPolicy>     class CountingPtr : private CounterPolicy, private ObjectPolicy {     private:         // shortcuts:         typedef CounterPolicy CP;         typedef ObjectPolicy  OP;           T* object_pointed_to;      // the object referred to (or NULL if none)       public:         // default constructor (no explicit initialization):         CountingPtr() {             this->object_pointed_to = NULL;         }           // a converting constructor (from a built-in pointer):         explicit CountingPtr(T* p) {             this->init(p);         // init with ordinary pointer         }           // copy constructor:         CountingPtr(CountingPtr<T, CP, OP> const& cp)             : CP((CP const&)cp),      // copy policies             OP((OP const&)cp) {             this->attach(cp);      // copy pointer and increment counter         }           // destructor:         ~CountingPtr() {             this->detach();        // decrement counter                                    //  (and dispose counter if last owner)         }           // assignment of a built-in pointer         CountingPtr<T, CP, OP>& operator= (T* p) {             // no counting pointer should point to *p yet:             assert(p != this->object_pointed_to);             this->detach();        // decrement counter                                    //  (and dispose counter if last owner)             this->init(p);         // init with ordinary pointer             return *this;         }           // copy assignment (beware of self-assignment):         CountingPtr<T, CP, OP>&             operator= (CountingPtr<T, CP, OP> const& cp) {             if (this->object_pointed_to != cp.object_pointed_to) {                 this->detach();    // decrement counter                                    //  (and dispose counter if last owner)                 CP::operator=((CP const&)cp);  // assign policies                 OP::operator=((OP const&)cp);                 this->attach(cp);  // copy pointer and increment counter             }             return *this;         }           // the operators that make this a smart pointer:         T* operator-> () const {             return this->object_pointed_to;         }           T& operator* () const {             return *this->object_pointed_to;         }           // additional interfaces will be added later         //...       private:         // helpers:         // - init with ordinary pointer (if any)         void init(T* p) {             if (p != NULL) {                 CounterPolicy::init(p);             }             this->object_pointed_to = p;         }           // - copy pointer and increment counter (if any)         void attach(CountingPtr<T, CP, OP> const& cp) {             this->object_pointed_to = cp.object_pointed_to;             if (cp.object_pointed_to != NULL) {                 CounterPolicy::increment(cp.object_pointed_to);             }         }           // - decrement counter (and dispose counter if last owner)         void detach() {             if (this->object_pointed_to != NULL) {                 CounterPolicy::decrement(this->object_pointed_to);                 if (CounterPolicy::is_zero(this->object_pointed_to)) {                     // dispose counter, if necessary:                     CounterPolicy::dispose(this->object_pointed_to);                     // use object policy to dispose the object pointed to:                     ObjectPolicy::dispose(this->object_pointed_to);                 }             }         } };         void test1()     {         std::cout << "\ntest1():\n";         CountingPtr<int> p0;         {             CountingPtr<int> p1(new int(42));             std::cout << "*p1: " << *p1 << std::endl;               *p1 = 17;             std::cout << "*p1: " << *p1 << std::endl;               CountingPtr<int> p2 = p1;             std::cout << "*p2: " << *p2 << std::endl;               *p1 = 33;             std::cout << "*p2: " << *p2 << std::endl;               p0 = p2;             std::cout << "*p0: " << *p0 << std::endl;               ++*p0;             ++*p1;             ++*p2;             std::cout << "*p0: " << *p0 << std::endl;             std::cout << "*p1: " << *p1 << std::endl;             std::cout << "*p2: " << *p2 << std::endl;         }         std::cout << "after block: *p0: " << *p0 << std::endl;     }       void test2()     {         std::cout << "\ntest2():\n";         { CountingPtr<int> p0(new int(42));         CountingPtr<int> p2 = p0;         }         CountingPtr<int> p1(new int(42));           std::cout << "qqq" << std::endl;           std::vector<CountingPtr<int> > coll;         std::cout << "qqq" << std::endl;         coll.push_back(p1);         std::cout << "qqq" << std::endl;         coll.push_back(p1);         std::cout << "qqq" << std::endl;           std::cout << "qqq" << std::endl;           ++*p1;         ++*coll[0];         std::cout << *coll[1] << std::endl;     }         int main()     {         test1();         test2();     }