19-父类的构造函数

写在前面

初始化列表有继承时，需要注意下父类的初始化构造参数。

码上建功

class Person {
    int m_age;
public:
    //父类的无参构造函数
    Person() {
        cout << "Person()" << endl;
    }
    //父类的有参构造函数
    Person(int age) :m_age(age) {
        cout << "Person(int age)" << endl;
    }
};

class Student : public Person {
    int m_score;
public:
    //子类的无参构造函数
    Student() {
        cout << "Student()" << endl;
    }
    //子类的无参构造函数
    Student(int age, int score) :m_score(score), Person(age) {
        cout << "Student(int age, int score)" << endl;
    }
};
调用
Student student;
Student student2(10,30);
打印结果；
Person()
Student()
Person(int age)
Student(int age, int score)
可以看出：
◼ 子类的构造函数默认会调用父类的无参构造函数
◼ 如果子类的构造函数显式地调用了父类的有参构造函数，就不会再去默认调用父类的无参构造函数


class Person {
    int m_age;
public:
    Person(int age) :m_age(age) {
        cout << "Person(int age)" << endl;
    }
};

class Student : public Person {
    int m_score;
public:
    Student() :Person(0) {

    }
};
◼ 如果父类缺少无参构造函数，子类的构造函数必须显式调用父类的有参构造函数
 

来看下析构函数

class Person {
    int m_age;
public:
    //父类的无参构造函数
    Person() {
        cout << "Person()" << endl;
    }
    //父类的有参构造函数
    Person(int age) :m_age(age) {
        cout << "Person(int age)" << endl;
    }
    ~Person() {
        cout << "~Person()" << endl;
    }
};

class Student : public Person {
    int m_score;
public:
    //子类的无参构造函数
    Student() {
        cout << "Student()" << endl;
    }
    //子类的无参构造函数
    Student(int age, int score) :m_score(score), Person(age) {
        cout << "Student(int age, int score)" << endl;
    }
    ~Student() {
        cout << "~Student" << endl;
    }
};
调用
Student *student = new Student();
delete student;
打印：
~Student
~Person()
构造和析构顺序相反，先调用子类的析构函数，先调用父类的构造函数

完整代码demo，请移步GitHub：DDGLearningCpp