郑莉cpp习题7-11

代码

#include <iostream>
using namespace std;

class BaseClass{
public:
    void fn1();
    void fn2();
};

void BaseClass::fn1(){
    cout << "调用基类的函数 fn1()" << endl;
}

void BaseClass::fn2(){
    cout << "调用基类的函数 fn2()" << endl;
}

class DerivedClass : public BaseClass{
public:
    void fn1();
    void fn2();
};

void DerivedClass::fn1(){
    cout << "调用派生类的函数 fn1()" << endl;
}

void DerivedClass::fn2(){
cout << "调用派生类的函数 fn2()" << endl;
}

int main()
{
    DerivedClass aDerivedClass;
    DerivedClass *pDerivedClass = &aDerivedClass;
    BaseClass *pBaseClass = &aDerivedClass;
    aDerivedClass.fn1();
    aDerivedClass.fn2();
    cout << "--------------" << endl;
    pBaseClass->fn1();
    pBaseClass->fn2();
    cout << "--------------" << endl;
    pDerivedClass->fn1();
    pDerivedClass->fn2();
}

结果可见，把子类的对象的地址赋值给父类的指针，执行同名的函数体只会执行父类的。因为赋值的过程中发生的向上转型。

调用派生类的函数 fn1()
调用派生类的函数 fn2()
--------------
调用基类的函数 fn1()
调用基类的函数 fn2()
--------------
调用派生类的函数 fn1()
调用派生类的函数 fn2()