C++之构造函数初始化列表

初始化列表特点

1. 一种便捷的初始化成员变量的方式
2.只能用在构造函数中
3.初始化顺序只跟成员变量的声明顺序有关

构造函数

struct Person {
    int m_age;
    int m_height;
    Person(int age, int height) {
        this->m_age = age;
        this->m_height = height;
    }
};

等价于

struct Person {
    int m_age;
    int m_height;
    Person(int age, int height) :m_height(height), m_age(m_height)   {

    }
};

#### 思考以下会打印成员变量值是多少

 Person person2(10, 20);
 person2.display();

int myAge() {
	cout << "myAge()" << endl;
	return 30;
}

int myHeight() {
	cout << "myHeight()" << endl;
	return 180;
}

Person(int age, int height) :m_height(myAge()), m_age(myHeight())   {

}
void display() {
    cout << "m_age is " << this->m_age << endl;
    cout << "m_height is " << this->m_height << endl;
}

构造函数的互相调用

构造函数调用构造函数,只能放在初始化列表调用(包括子类调用父类),其格式如下调用示例

Person() :Person(0, 0) { }
Person(int age, int height) :m_age(age), m_height(height) { }

错误示例

Person() :Person(0, 0) {
    cout << "Person() " << this << endl;

    // 直接调用构造函数，会创建一个临时对象，传入一个临时的地址值给this指针
    // Person(0, 0);
}
Person(int age, int height) {
    cout << "Person(int age, int height) " << this << endl;

    this->m_age = age;
    this->m_height = height;
}