C++构造函数初始化列表与赋值_c++ 类构造函数参数列表

class Animal
{
public:
    Animal(int weight,int height):       //A初始化列表
      m_weight(weight),
      m_height(height)
    {
    }
    Animal(int weight,int height)       //B函数体内初始化
    {
        m_weight = weight;
        m_height = height;
    }
private:
    int m_weight;
    int m_height;
};

class Animal
{
public:
    Animal(int weight,int height):        //没有提供无参的构造函数 
      m_weight(weight),
      m_height(height)
    {
}
private:
    int m_weight;
    int m_height;
};

class Dog: public Animal
{
public:
    Dog(int weight,int height,int type)   //error 构造函数 父类Animal无合适构造函数
    {
    }
private:
    int m_type;
};

class Dog: public Animal
{
public:
    Dog(int weight,int height,int type):
        Animal(weight,height)         //必须使用初始化列表增加对父类的初始化
    {
        ;
    }
private:
    int m_type;
};

class Dog: public Animal
{
public:
    Dog(int weight,int height,int type):
        Animal(weight,height), 
        LEGS(4)                //必须在初始化列表中初始化
    {
        //LEGS = 4;           //error
    }
private:
    int m_type;
    const int LEGS;
};

class Food
{
public:
    Food(int type = 10)
    {
        m_type = 10;
    }
    Food(Food &other)                 //拷贝构造函数
    {
        m_type = other.m_type;
    }
    Food & operator =(Food &other)      //重载赋值=函数
    {
        m_type = other.m_type;
        return *this;
    }
private:
    int m_type;
};

（1）构造函数赋值方式 初始化成员对象m_food
class Dog: public Animal
{
public:
    Dog(Food &food)
      //:m_food(food)  
    {
        m_food = food;               //初始化 成员对象
    }
private:
    Food m_food;
};
//使用
Food fd;
Dog dog(fd);   //
Dog dog(fd);结果：
先执行了   对象类型构造函数Food(int type = 10)——> 
然后在执行 对象类型构造函数Food & operator =(Food &other)
想象是为什么？



（2）构造函数初始化列表方式
class Dog: public Animal
{
public:
    Dog(Food &food)
      :m_food(food)                  //初始化 成员对象
    {
        //m_food = food;               
    }
private:
    Food m_food;
};
//使用
Food fd;
Dog dog(fd);   //
Dog dog(fd);结果：执行Food(Food &other)拷贝构造函数完成初始化