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C++ 智能指針
最近在做Windows上管理USB手機終端的相關程序。
實際情況：
Class Phone *symbian = new Phone();
Class ConnectManager, Class CommManager都需要對symbian指針進行引用和維護(保留一個拷貝)。
但是這樣就導致了symbian何時可以被delete？
在ConnectManager析構函數中delete? 這將導致CommManager無法使用symbian了。
在CommManager中delete symbian也是同樣的道理。
在參考了《C++ Primer》之後，自己動手寫一個智能指針
代碼如下
#include <iostream> using namespace std; class ConnectManager; class CommManager; class Phone { public: Phone() { cout << "Hello World!" << endl; } ~Phone() { cout << "Bye!" << endl; } }; class U_ptr { friend class ConnectManager; friend class CommManager; public: U_ptr(Phone *pH): use(0), pPhone(pH) { } ~U_ptr() { delete pPhone; } private: Phone *pPhone;//這裏是關鍵，轉移數據的宿主 size_t use; }; class ConnectManager { public: ConnectManager(U_ptr *p): pUptr(p) { ++pUptr->use; cout << "ConnectManager: Hi I get the Phone" << endl; cout << pUptr->use << " users" << endl; } ~ConnectManager() { cout << "ConnectManaer: Can I delete the Phone?" << endl; if (--pUptr->use == 0) { cout << "Yes, You can" << endl; delete pUptr; } else { cout << "No, You can't, The Phone is in use" << endl; cout << pUptr->use << " users" << endl; } } private: U_ptr *pUptr; }; class CommManager { public: CommManager(U_ptr *p): pUptr(p) { ++pUptr->use; cout << "CommManager: Hi I get the Phone" << endl; cout << pUptr->use << " users" << endl; } ~CommManager() { cout << "CommManager: Can I delete the Phone" << endl; if (--pUptr->use == 0) { cout << "Yes, You can" << endl; } else { cout << "No, You can't. The Phone is in use" << endl; cout << pUptr->use << " users" << endl; } } private: U_ptr *pUptr; }; int main(void) { Phone *symbian = new Phone(); U_ptr *pU = new U_ptr(symbian); ConnectManager connManager = ConnectManager(pU); CommManager commManager = CommManager(pU); }
運行結果如下：
Hello World!
ConnectManager: Hi I get the Phone
1 users
CommManager: Hi I get the Phone
2 users
CommManager: Can I delete the Phone?
No, You Can't. The Phone is in use;
1 users
ConnectManager: Can I delete the Phone?
Yes. You can
Bye!
代碼中已經注釋出來了。智能指針的關鍵是轉交數據的宿主。雖然Phone是給CommManager和ConnectManager使用，
但是，真正的Phone要由智能指針類去維護。
最後更新：2017-04-02 06:51:37