19-父類的構造函數

寫在前面

初始化列表有繼承時，須要注意下父類的初始化構造參數。
複製代碼

碼上建功

class Person {
    int m_age;
public:
    //父類的無參構造函數
    Person() {
        cout << "Person()" << endl;
    }
    //父類的有參構造函數
    Person(int age) :m_age(age) {
        cout << "Person(int age)" << endl;
    }
};

class Student : public Person {
    int m_score;
public:
    //子類的無參構造函數
    Student() {
        cout << "Student()" << endl;
    }
    //子類的無參構造函數
    Student(int age, int score) :m_score(score), Person(age) {
        cout << "Student(int age, int score)" << endl;
    }
};
調用
Student student;
Student student2(10,30);
打印結果；
Person()
Student()
Person(int age)
Student(int age, int score)
能夠看出：
◼ 子類的構造函數默認會調用父類的無參構造函數
◼ 若是子類的構造函數顯式地調用了父類的有參構造函數，就不會再去默認調用父類的無參構造函數


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) {

    }
};
◼ 若是父類缺乏無參構造函數，子類的構造函數必須顯式調用父類的有參構造函數
 
複製代碼

來看下析構函數

class Person {
    int m_age;
public:
    //父類的無參構造函數
    Person() {
        cout << "Person()" << endl;
    }
    //父類的有參構造函數
    Person(int age) :m_age(age) {
        cout << "Person(int age)" << endl;
    }
    ~Person() {
        cout << "~Person()" << endl;
    }
};

class Student : public Person {
    int m_score;
public:
    //子類的無參構造函數
    Student() {
        cout << "Student()" << endl;
    }
    //子類的無參構造函數
    Student(int age, int score) :m_score(score), Person(age) {
        cout << "Student(int age, int score)" << endl;
    }
    ~Student() {
        cout << "~Student" << endl;
    }
};
調用
Student *student = new Student();
delete student;
打印：
~Student
~Person()
構造和析構順序相反，先調用子類的析構函數，先調用父類的構造函數
複製代碼

完整代碼demo，請移步GitHub：DDGLearningCpp