简单的问题求解答
本帖最后由 yuanhaosh 于 2013-01-28 14:20:07 编辑 问题在1，2还望大家不吝惜赐教

#include <iostream.h>
class Base
{
public:
void f(int x){ cout << "Base::f(int) " << x << endl; }
void f(float x){ cout << "Base::f(float) " << x << endl; }
virtual void g(void){ cout << "Base::g(void)" << endl;}
};
class Derived : public Base
{
public:
virtual void g(void){ cout << "Derived::g(void)" << endl;}
};
void main(void)
{

Derived d; //直接用d.g()也行啊，为什么要这样 ？1111111111111111111
Base *pb = &d; //这样做的好处是什么？22222222222222222222222


pb->f(42); // Base::f(int) 42

pb->f(3.14f); // Base::f(float) 3.14
pb->g(); // Derived::g(void)

d.g();
        d.f(324);
d.f(324.00f);
}

[解决办法]
C++的精华可谓就在于多态了。多态的实现只能靠指针和引用。
[解决办法]
利用引用和指针来实现多态
[解决办法]
简单的代码，是看不出多态的好处的。

# include <iostream>
# include <vector>

using namespace std;

class Shape {
public:
    virtual double area() = 0;
    virtual ~Shape() {}
};

class Square : public Shape {
    double side;
public:
    Square(double side) { this->side = side; }
    double area() {
        return side * side;
    }
};

class Rectangle : public Shape {
    double a, b;
public:
    Rectangle(double a, double b) { this->a = a; this->b = b; }
    double area() {
        return a * b;
    }
};

class Circle : public Shape {
    double r;
public:
    Circle(double r) { this->r = r; }
    double area() {
        return 3.14 * r * r;
    }
};

int main()
{
    vector<Shape *> v;
    v.push_back(new Square(4));
    v.push_back(new Rectangle(3, 4));
    v.push_back(new Circle(4));

    vector<Shape *>::iterator it = v.begin();
    for (; it != v.end(); it++)
        cout << (*it)->area() << endl;

    it = v.begin();
    for (; it != v.end(); it++) 
 
        delete (*it);

    return 0;
}