1 #include<iostream>
 2 using namespace std;
 3 
 4 class Base1{
 5     public:
 6         Base1(int i){
 7             cout<<"Base1 "<<i<<endl;
 8         }
 9 }; 
10 
11 class Base2{
12     public:
13         Base2(int j){
14             cout<<"Base2 "<<j<<endl;
 
15         }
16 }; 
17 
18 class Derived:public Base2, public Base1{
19     public:
20         Derived(int a,int b,int c,int d):Base1(a),member1(c),member2(d),Base2(b){}
21     private:
22         Base1 member1;
23         Base2 member2;
24 };
25 
26 int main()
27 {
28     Derived obj(1,2
 
,3,4);
29 }

這是一個派生類構造函數的例子，照書上打的，簡化了一些。

在Derived類構造函數中，先調用基類的構造函數，然後調用內嵌對象的構造函數。

調用順序先按這裏的順序來

class Derived:public Base2, public Base1{……}
先是Base2,再是Base1

然後是按這邊的順序

private:
         Base1 member1;
         Base2 member2;
先是Base1,再是Base2

 1 #include<iostream>
 2 using namespace
 
 std;
 3 
 4 class Base1{
 5     public:
 6         Base1(int i){
 7             cout<<"Base1 "<<i<<endl;
 8         }
 9 }; 
10 
11 class Base2{
12     public:
13         Base2(int j){
14             cout<<"Base2 "<<j<<endl;
15         }
16 }; 
17 
18 class DD:public Base1, public Base2{
19     public:
20         DD(int a,int b):Base1(a),Base2(b){}
21     private:
22         Base1 member1;
23         Base2 member2;
24 };
25 
26 int main()
27 {
28     DD obj(1,2);
29 }

如果我把代碼改成這樣，只初始化基類，而不初始化內嵌對象，就會報錯no matching function for call to ‘Base1::Base1()’

我在把代碼改一下，變成這樣

 1 #include<iostream>
 2 using namespace std;
 3 
 4 class Base1{
 5     public:
 6         Base1(int i=0){
 7             cout<<"Base1 "<<i<<endl;
 8         }
 9 }; 
10 
11 class Base2{
12     public:
13         Base2(int j=0){
14             cout<<"Base2 "<<j<<endl;
15         }
16 }; 
17 
18 class DD:public Base1, public Base2{
19     public:
20         DD(int a,int b,int c,int d):member1(c),member2(d){}
21     private:
22         Base1 member1;
23         Base2 member2;
24 };
25 
26 int main()
27 {
28     DD obj(1,2,3,4);
29 }

也就是把基類的構造函數的參數初始化了，這也相當於一種默認構造函數。編譯就通過了。
應該是如果初始化列表裏的初始化不完全的話，程序就會去找類的默認構造函數，因為之前代碼的類的構造函數，有參數，且沒有初始化，所以就找不到默認構造函數，於是報錯。

派生類構造函數