类成员是另一个类时会默认初始化

 1 #include <iostream>
 2 using namespace std;
 3 
 4 class SlaveClass
 5 {
 6 public:
 7     SlaveClass()
 8     {
 9         cout << "The construction of slave class" << endl;
10     }
11 };
12 
13 
14 class MasterClass
15 {
16 public:
17     MasterClass()
18     {
19         cout << "The construction of master class" << endl;
20     }
21 private:
22     int m;
23     SlaveClass sc;
24 };
25 
26 
27 
28 int main()
29 {
30     MasterClass mc = MasterClass();
31 };

输出

The construction of slave class

The construction of master class