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1,如果基类没有default构造函数,则意味着其不能自己初始化。如果其被派生,派生类的构造函数要负责调用基类的构造函数,并传递给它需要的参数。下例中Base
2,如果类成员没有默认构造函数。下例中Elem4
2,如果类的成员变量中含有const成员变量,如果不使用列表,在构造函数中是不能对其赋值的,会导致编译失败。下例中b
3,如果类的成员变量中含有引用,引用必须被初始化。下例中c
4,需要提高效率的时候,如果不使用初始化列表,而放在构造函数体内赋值的方法,则变量先被默认构造函数初始化,然后又调用copy构造函数。
1 /////////////////////////////////////////////////////////////////////////////// 2 // 3 // FileName : constructor.h 4 // Version : 0.10 created 2013/11/09 00:00:00 5 // Author : Jimmy Han 6 // Comment : 7 // 8 /////////////////////////////////////////////////////////////////////////////// 9 #include <iostream> 10 using namespace std; 11 12 class Elem1{ 13 public: 14 Elem1(int x){ 15 cout << "Elem1() was called." << endl; 16 } 17 ~Elem1(){ 18 cout << "~Elem1() was called." << endl; 19 } 20 }; 21 22 class Elem2{ 23 public: 24 Elem2(int x){ 25 cout << "Elem2() was called." << endl; 26 } 27 ~Elem2(){ 28 cout << "~Elem2() was called." << endl; 29 } 30 }; 31 32 class Elem3{ 33 public: 34 Elem3(int x){ 35 cout << "Elem3() was called." << endl; 36 } 37 ~Elem3(){ 38 cout << "~Elem3() was called." << endl; 39 } 40 }; 41 42 class Elem4{ 43 public: 44 Elem4(int x){ 45 cout << "Elem4() was called." << endl; 46 } 47 ~Elem4(){ 48 cout << "~Elem4() was called." << endl; 49 } 50 }; 51 52 53 class Base{ 54 public: 55 Base(int):_elem2(Elem2(2)), _elem1(Elem1(1)), _elem3(Elem3(3)){ 56 cout << "Base() was called." << endl; 57 } 58 ~Base(){ 59 cout << "~Base() was called." << endl; 60 } 61 private: 62 Elem1 _elem1; 63 Elem2 _elem2; 64 Elem3 _elem3; 65 }; 66 67 class Derive : public Base{ 68 public: 69 //if there is no default constructor for base class, it has to be called explicit in derive class 70 //four scenarios to use initialization list must: 71 //1. Base. base class don‘t have Base(); 72 //2. const int b. class member is const 73 //3. int& c. class member is reference 74 //4. _elem4. class member dont‘ have default constructor. 75 Derive():Base(1), _elem4(Elem4(4)), b(3), c(b){ 76 cout << "Derive() was called." << endl; 77 } 78 private: 79 Elem4 _elem4; 80 const int b; 81 const int& c; 82 83 };
1 /////////////////////////////////////////////////////////////////////////////// 2 // 3 // FileName : constructor_client.cc 4 // Version : 0.10 5 // Author : Ryan Han 6 // Date : 2013/11/19 7 // Comment : 8 // Elem1() was called. 9 // Elem2() was called. 10 // Elem3() was called. 11 // Base() was called. 12 // Elem4() was called. 13 // Derive() was called. 14 // ~Elem4() was called. 15 // ~Base() was called. 16 // ~Elem3() was called. 17 // ~Elem2() was called. 18 // ~Elem1() was called. 19 // 20 /////////////////////////////////////////////////////////////////////////////// 21 #include <iostream> 22 #include "constructor.h" 23 using namespace std; 24 25 int main(){ 26 Derive d1; 27 28 return 0; 29 }
什么时候需要在类的构造函数中使用初始化列表,布布扣,bubuko.com
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原文地址:http://www.cnblogs.com/dracohan/p/3807304.html