c++基础 类的声明与使用

[wuyuedefeng]

#include <iostream>

class Animal {
public:
    virtual void speak() {
        std::cout << "Animal speak" << std::endl;
    }
protected:
    std::string name;
    int age;
};

// virtual 解决菱形继承, B -> A, C -> A, D -> B&C, 使D只保留一份A
class Dog: public /*virtual*/ Animal {
    // 友元 该函数内可以访问私有变量
    friend void printDogInfo(Dog &dog);
public:
    // 构造函数
    Dog() {
        std::cout << "默认构造函数" << std::endl;
        name = "unknown";
        age = 0;
    }
    Dog(std::string name, int age = 0) {
        std::cout << "有参构造函数" << std::endl;
        this -> name = name;
        this -> age = age;
    }
    void speak() {
        std::cout << "Dog speak" << std::endl;
    }

    ~Dog() {
        std::cout << "析构函数: " << name << std::endl;
    }
};

void printDogInfo(Dog &dog) {
    std::cout << "name: " << dog.name << " age: " << dog.age << std::endl;
}


int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";

    Dog dog;
    dog.speak();
    printDogInfo(dog);

    {
        Animal *dog2 = new Dog("二哈");
        // 这里期望调用Dog的speak，所以Animal内的speak需要使用虚函数
        dog2 -> speak();

        delete dog2;
    }

    return 0;
}