1:看上去像多态
答案:
#include <iostream>
using namespace std;
class B {
private:
int nBVal;
public:
void Print()
{ cout << "nBVal="<< nBVal << endl; }
void Fun()
{cout << "B::Fun" << endl; }
B ( int n ) { nBVal = n;}
};
class D:public B{
private:
int tt;
public:
void Print(){
B::Print();
cout<<"nDVal="<<tt<<endl;
}
void Fun(){
cout<<"D:Fun"<<endl;
}
D(int t_):B(3*t_), tt(t_){}
};
int main() {
B * pb; D * pd;
D d(4); d.Fun();//D的带参构造函数,调用d的fun
pb = new B(2); pd = new D(8);
pb -> Fun(); pd->Fun();
pb->Print ();
pd->Print ();//这里是24,这里调用了pd的Print,如果不重写,就只能调用B的了
pb = & d;
pb->Fun();//B::Fun
pb->Print();//nBVal=12
return 0;
}
/*
D::Fun
B::Fun
D::Fun
nBVal=2
nBVal=24
nDVal=8
B::Fun
nBVal=12
*/
2、fun和do
#include <iostream>
using namespace std;
class A {
private:
int nVal;
public:
void Fun()
{ cout << "A::Fun" << endl; };
void Do()
{ cout << "A::Do" << endl; }
};
class B:public A {
public:
virtual void Do()
{ cout << "B::Do" << endl;}
};
class C:public B {
public:
void Do( ) //这里是一个虚函数
{ cout <<"C::Do"<<endl; }
void Fun()
{ cout << "C::Fun" << endl; }
};
void Call(
B &p // 这个位置,设置为B的引用,由于B的Do是虚函数,因此C的函数D也是虚函数,调用C的do函数,
// 但是调用Fun是由于继承,因此调用到了A的Fun方法。
) {
p.Fun(); p.Do();
}
int main() {
C c;
Call( c);
return 0;
}
/*
A::Fun
C::Do
*/
3、这是什么鬼delete
#include <iostream>
using namespace std;
class A
{
public:
A() { }
virtual ~A(){
cout<<"destructor A"<<endl;//这里设置为虚析够函数,才可以在delete的时候先消子类在消父类
}
};
class B:public A {
public:
~B() { cout << "destructor B" << endl; }
};
int main()
{
A * pa;
pa = new B;
delete pa;
return 0;
}
/*
destructor B
destructor A
*/
4、怎么又是fun和do
#include <iostream>
using namespace std;
class A {
private:
int nVal;
public:
void Fun()
{ cout << "A::Fun" << endl; };
virtual void Do()
{ cout << "A::Do" << endl; }
};
class B:public A {
public:
virtual void Do()
{ cout << "B::Do" << endl;}
};
class C:public B {
public:
void Do( )
{ cout <<"C::Do"<<endl; }
void Fun()
{ cout << "C::Fun" << endl; }
};
void Call(A *p) {
p->Fun(); p->Do();//这里传入c类的时候,由于Do一直都是虚函数,因此会按照继承的顺序向上找,因此会输出A:Do了
}
int main() {
Call( new A());
Call( new C());
return 0;
}
/*
A::Fun
A::Do
A::Fun
C::Do
*/