geeksforgeeks 027-默认构造函数

#include <iostream>
using namespace std;
 
class Base
{
public:
    
};
 
class A
{
public:
    // User defined constructor
    A()
    {
        cout << "A Constructor" << endl;
    }
 
    // uninitialized
    int size;
};
 
class B : public A
{
    // compiler defines default constructor of B, and
    // inserts stub to call A constructor
 
    // compiler won't initialize any data of A
};
 
class C : public A
{
public:
    C()
    {
        // User defined default constructor of C
        // Compiler inserts stub to call A's construtor
        cout << "B Constructor" << endl;
 
        // compiler won't initialize any data of A
    }
};
 
class D
{
public:
    D()
    {
        // User defined default constructor of D
        // a - constructor to be called, compiler inserts
        // stub to call A constructor
        cout << "D Constructor" << endl;
 
        // compiler won't initialize any data of 'a'
    }
 
private:
    A a;
};
 
int ()
{
    Base base;
 
    B b;
    C c;
    D d;
 
    return 0;
}

A Constructor
A Constructor
B Constructor
A Constructor
D Constructor