C++學習記錄（九）智慧指標、異常處理
阿新 • • 發佈：2022-05-14
這是第九天的學習。
1 #include <iostream> 2 #include <memory> 3 4 using namespace std; 5 class A 6 { 7 int id; 8 public: 9 A(int id) : id(id) { cout << "A" << endl; } 10 ~A() { cout << "~A" << endl; } 11 12 void showInfo() { cout << this->id << endl; } 13 }; 14 15 template <class T> 16 class AutoPtr 17 { 18 private: 19 T* p; 20 public: 21 AutoPtr(T* _p) : p(_p) {} 22 ~AutoPtr() { delete p; } 23 24 T* get() { return this->p; } 25 AutoPtr(AutoPtr& autoptr) 26 { 27 this->p = autoptr.p; 28 autoptr.p = nullptr; 29 } 30 }; 31 32 template<class T> 33 class Count // 定義一個計數器模板 34 { 35 private: 36 T* p; // 定義指標 37 int m_count; // 定義計數值 38 public: 39 Count(T* _p = nullptr) : p(_p)40 { // 建構函式，當指標p不為空時，計數值為1 41 if(p != nullptr) m_count = 1; 42 cout << "Count" << endl; 43 } 44 ~Count() { cout << "~Count" << endl; } 45 46 // 計數器加法 47 void Add() { this->m_count++; } 48 // 計數器減法 49 int Sub() { return --m_count; } 50 int getCount() { return this->m_count; } 51 }; 52 53 template <class T> 54 class SharedPtr // 定義一個共享指標 55 { 56 private: 57 T* p; 58 //static int numb; // 靜態變數所有類共享，不安全 59 Count<T>* count; // 定義計數器 60 public: 61 SharedPtr(T* _p = nullptr) : p(_p) 62 { // 建構函式，新建計數器 63 if (p != nullptr) 64 { 65 count = new Count<T>(p); 66 } 67 } 68 //~SharedPtr() { if (numb == 0) delete p; else numb--; } 69 ~SharedPtr() 70 { 71 if (count->Sub() == 0) 72 { 73 delete this->p; 74 delete this->count; 75 p = nullptr; 76 count = nullptr; 77 } 78 //else numb--; 79 } 80 81 T* get() { return this->p; } 82 SharedPtr(const SharedPtr& sharedptr) : p(sharedptr.p),count(sharedptr.count) 83 { // 拷貝建構函式 84 if (p != nullptr) count->Add(); 85 //numb++; 86 cout << "copy constructor" << endl; 87 } 88 SharedPtr& operator=(const SharedPtr& sharedptr) 89 { 90 this->p = sharedptr.p; 91 this->count = sharedptr.count; 92 count->Add(); 93 return *this; 94 } 95 int useCount() { return count->getCount(); } 96 97 }; 98 99 //template <class T> 100 //int SharedPtr<T>::numb = 0; 101 102 int main() 103 { 104 // -1- 智慧指標，是一個類模板 105 // auto_ptr(棄用),shard_ptr(共享智慧指標),unqiue_ptr(唯一指標) 106 107 A* p1 = new A(123); 108 p1->showInfo(); 109 delete p1; 110 /* 111 auto_ptr<A> p2(new A(456)); // auto_ptr在C++17中被廢棄了 112 p2.get()->showInfo(); 113 114 auto_ptr<A> p3(p2); // 呼叫拷貝構造 115 p3.get()->showInfo(); 116 p2.get()->showInfo(); // p2賦值給p3後變為空指標 117 */ 118 /* 119 AutoPtr<A> p4(new A(789)); 120 p4.get()->showInfo(); 121 122 AutoPtr<A> p5(p4); 123 p5.get()->showInfo(); 124 */ 125 126 // 127 /* 128 shared_ptr<A> p6(new A(147)); 129 p6.get()->showInfo(); 130 shared_ptr<A> p7(p6); 131 p7.get()->showInfo(); 132 p6.get()->showInfo(); 133 */ 134 /* 135 SharedPtr<A> p8(new A(258)); 136 p8.get()->showInfo(); 137 SharedPtr<A> p9(p8); 138 p9.get()->showInfo(); 139 p8.get()->showInfo(); 140 */ 141 // 142 SharedPtr<A> ptr1(new A(100)); 143 SharedPtr<A> ptr2(ptr1); 144 SharedPtr<A> ptr3; 145 ptr3 = ptr2; 146 cout << " " << ptr3.useCount() << endl; 147 148 //cout << "Hello World!" << endl; 149 return 0; 150 }
1 #include <iostream> 2 #include <memory> 3 4 using namespace std; 5 class B; // 前置宣告 6 class A 7 { 8 public: 9 weak_ptr<B> ptr_b; 10 public: 11 A() { cout << "A" << endl; } 12 ~A() { cout << "~A" << endl; } 13 void showInfo() { cout << "ShowInfo" << endl; } 14 }; 15 class B 16 { 17 public: 18 weak_ptr<A> ptr_a; 19 public: 20 B() { cout << "B" << endl; } 21 ~B() { cout << "~B" << endl; } 22 23 void func() 24 { 25 // 提升對物件的許可權 26 shared_ptr<A> temp = this->ptr_a.lock(); 27 if( temp != nullptr ) 28 { 29 temp->showInfo(); 30 } 31 } 32 }; 33 34 int main() 35 { 36 // weak_ptr,沒有物件的訪問權 37 // 定義物件時用shared_ptr,用new,否則用weak_ptr 38 shared_ptr<A> pA(new A); 39 shared_ptr<B> pB(new B); 40 41 pA->ptr_b = pB; 42 pB->ptr_a = pA; 43 44 cout << pA.use_count() << endl; 45 cout << pB.use_count() << endl; 46 47 cout << "Hello World!" << endl; 48 return 0; 49 }
1 #include <iostream> 2 3 using namespace std; 4 5 //class Error 6 //{ 7 //private: 8 // string errorMsg; 9 //public: 10 // Error(string errorMsg) { this->errorMsg = errorMsg; } 11 // string What() { return this->errorMsg; } 12 13 //}; 14 //Error err("b must not be 0"); 15 logic_error err("b must not be 0"); 16 17 float fun_div(int a, int b) 18 { 19 if ( b==0 ) 20 { 21 //throw -1; 22 throw err; 23 } 24 return a/b; 25 } 26 int fun_add(int a, int b) 27 { 28 return fun_div(a,b) + a + b; 29 } 30 int fun_mul(int a, int b) 31 { 32 return fun_add(a,b) * a * b; 33 } 34 35 int main() 36 { 37 // 面向異常處理機制的框架 38 // throw關鍵字：丟擲異常, throw + 類物件 或基本型別的值 39 // 捕捉異常try{...丟擲異常的闡述...}catch() 40 // 處理異常catch(異常數型 異常的物件或變數){...異常處理語句塊...} 41 int data; 42 int a = 10; 43 int b = 0; 44 try 45 { 46 data = fun_mul(a,b); 47 cout << "final data is " << data << endl; 48 } 49 /* 50 catch (int e) 51 { 52 if ( e== -1 ) { cout << "b must not be 0" << endl; } 53 } 54 */ 55 /* 56 catch (Error& e) 57 { 58 cout << e.What() << endl; 59 } 60 */ 61 catch (logic_error& e) 62 { 63 cout << e.what() << endl; 64 } 65 66 cout << "Hello World!" << endl; 67 return 0; 68 }