如何运行抽象class函数和继承的函数？

Question

刚学了abstractclass，但不是很懂。是否有可能运行抽象 class 函数和继承函数一次全部？..

例如，

class Animals
{
 public:
    virtual void Display() = 0;
};

class Dog : public Animals
{
    void Display()
    {
        cout << "This is Dog!" << endl;
};

class Cat : public Animals
{
    void Display()
    {
        cout << "This is Cat!" << endl;
    }
};

我还有另一个名为 Zoo 的 class，它将运行 class Animals

中的抽象函数

class Zoo : public Animals
{
   Animals* animal;
   animal->Display();
}

我想要的输出是

This is Dog!
This is Cat!

当我运行这个时，它有错误..还有其他方法可以得到这个输出吗？谢谢:)

Answer 1

首先，有一个语法错误：

 class Animals
{
 public:
    virtual void Display() = 0;
};

class Dog : public Animals
{
    void Display()
    {
        cout << "This is Dog!" << endl;
    }
};

class Cat : public Animals
{
    void Display()
    {
        cout << "This is Cat!" << endl;
    }
};

然后，如果你想创建 Dog 和 Cat 实例，你可以为它们调用新的运算符类:

class Zoo : public Animals
{
   void Display() 
   {
       Animals* animal1;
       animal1 = new Cat();
       animal1->Display();
       delete animal1;

       Animals* animal2;
       animal2 = new Dog();
       animal2->Display();
       delete animal2;
   }

}

这应该会得到您想要的输出。

Answer 2

Is there a way to only call the base class and run the inherited classes too?

我想你想要这个：

#include <iostream>
#include <memory>

class Animals
{
public:
    virtual void Display() = 0;
    virtual ~Animals() = default;
};

class Dog : public Animals
{
    void Display() override
    {
        std::cout << "This is Dog!" << std::endl;
    }
};

class Cat : public Animals
{
    void Display() override
    {
        std::cout << "This is Cat!" << std::endl;
    }
};

class Goat : public Animals
{
    void Display() override
    {
        std::cout << "This is Goat!" << std::endl;
    }
};

int main()
{
    Animals* animal = new Dog;
    animal->Display();
    delete animal; // delete at some point to avoid memory leak as Dog is allocated on the heap

    Cat cat;
    animal = &cat;
    animal->Display(); // no delete needed, as Cat is allocated on the stack and will cleared when goes out of scope

    std::unique_ptr<Animals> animal2 = std::make_unique<Goat>();
    animal2->Display(); // no delete needed, Goat is allocated on the heap but will be cleared when goes out of scope

    return 0;
}

https://ideone.com/yoVt4G

加入 std::unique_ptr 以增加多样性

Answer 3

animal->Display(); 导致未定义行为，因为 animal 未初始化，因此首先将其初始化为

    Cat my_cat;
    Animals* animal = &my_cat;
    animal->Display();

或

 Animals* animal = new Cat();
 animal->Display();
 ....
 delete  animal;

这是你的代码，解释在评论中。

class Animals {
        public:
                virtual void Display() = 0;/*its a PVF , in every derived class it should be re-defined */
};

class Dog : public Animals {
        void Display() {
                cout << "This is Dog!" << endl;
        };
};
class Cat : public Animals {
        void Display() {
                cout << "This is Cat!" << endl;
        }
};

class Zoo : public Animals {
        public :
                void Display() {
                        #if 1
                        Dog my_dog;
                        Animals *animal = &my_dog; /** Display() of Animal class will be invoked  bcz Display() is declared as  virtual */
                        animal->Display();
                        #endif
                        #if 0
                        Animals* animal = new Cat(); /** Display() of Cat class  eill be invoked */
                        animal->Display();
                        delete animal;
                        #endif
                }
};
int main() {
        Zoo my_zoo;
        my_zoo.Display();
        return 0;
}

希望对你有帮助。

如何运行抽象class函数和继承的函数？

How to run abstract class functions and the inherited functions?

c++

inheritance

class

abstract