什么时候需要在类的构造函数中使用初始化列表

 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 }