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Constructor usgae in the base type and the derived type

• When the constructor of the derived class is defined, we should consider and ensure how the base type is initialized:
  • If the base type has default constructor, the constructor in the derived class may ignore the initialization for the memebers in base type.
  • If the base type have no default constructor, the constructor in the derived class should explict initialize the base type in the initialization list via the user defined base type constructor.

// testing.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "stdio.h"
#include <iostream>

using namespace std;

class BASE
{
public:
    BASE(int x):i(x){};
    BASE(){};
private:
    int i;
};

class derived: public BASE
{
public:
    derived(int x):BASE(x)
    {
        j = x;
        //this->BASE::BASE(x);
    };
private:
    int j;
};

class grandson: public derived
{
public:
    grandson(int x, int y):derived(y),j(x){}; //use the defined constructor for derived because no defual contructor defined
private:
    int j;
};

int _tmain(int argc, _TCHAR* argv[])
{
    int a = 0;
    cout <<"debugging";

    BASE base_obj(5);
    BASE base_obj_2(7);

    BASE *ptr = &base_obj;
    BASE *ptr_b = ptr;

    int sizeofobj = (int)sizeof(base_obj);

    ptr = (BASE*)((char*)ptr + sizeofobj);

    derived der_obj(6);
    derived der_obj_2(9);

    //der_obj_2 = base_obj; //there is no acceptable conversion from BASE -> Derived

    base_obj_2 = der_obj;

    return 0;
}

posted on 2007-10-21 23:29 everspring79 閱讀(277) 評論(0)  編輯 收藏 引用 所屬分類: Notes