C++多态的使用

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
class Animal
{
public:
    virtual void speak()
    {
        printf("Animal is Speaking\n");
    }
};
class dog : public Animal
{
public:
    virtual void speak()    //这里的virtual可写可不写
    {
        printf("dog is Speaking\n");
    }
};
class cat : public Animal
{
public:
    virtual void speak()    //这里的virtual可写可不写
    {
        printf("cat is Speaking\n");
    }
};
void test1(Animal &a)
{
    a.speak();
}
void test2(Animal *a)
{
    a->speak();
}
int main()
{
    dog g;
    cat t;
    test1(t);
    dog * ptr = &g;
    test2(ptr);
    return 0;
}