c++构造和析构顺序

c++构造和析构顺序

结论

• 构造顺序：
  • 按照继承顺序调用基类的构造函数。
  • 按照声明顺序调用成员变量的构造函数。
  • 调用派生类的构造函数（体）。
• 析构顺序（与构造顺序完全相反）：
  • 调用派生类的析构函数（体）。
  • 按照声明顺序的反序调用成员变量的析构函数。
  • 按照继承顺序的反序调用基类的析构函数。

例子

#include <iostream>

using namespace std;

class Base1 {
public:
    Base1() {
        cout << "Base1()" << endl;
    }

    virtual ~Base1() {
        cout << "~Base1()" << endl;
    }
};

class Base2 {
public:
    Base2() {
        cout << "Base2()" << endl;
    }

    virtual ~Base2() {
        cout << "~Base2()" << endl;
    }
};

class Member1 {
public:
    Member1() {
        cout << "Member1()" << endl;
    }

    ~Member1() {
        cout << "~Member1()" << endl;
    }
};

class Member2 {
public:
    Member2() {
        cout << "Member2()" << endl;
    }

    ~Member2() {
        cout << "~Member2()" << endl;
    }
};

class Member3 {
public:
    Member3() {
        cout << "Member3()" << endl;
    }

    ~Member3() {
        cout << "~Member3()" << endl;
    }
};

class Dervied : public Base1, public Base2 {
public:
    Dervied() : m3(), m1() {
        cout << "Dervied()" << endl;
    }
    ~Dervied() {
        cout << "~Dervied()" << endl;
    }

private:
    Member1 m1;
    Member2 m2;
    Member3 m3;
};

class Dervied2 : public Base2, public Base1 {
public:
    Dervied2() : m2(), m3(), m1() {
        cout << "Dervied()" << endl;
    }
    ~Dervied2() {
        cout << "~Dervied()" << endl;
    }

private:
    Member1 m1;
    Member2 m2;
    Member3 m3;
};

int main() {
    Base1 *b = new Dervied();
    cout << "---------------------" << endl;
    delete b;
    cout << "---------------------" << endl;
    Base1 *b1 = new Dervied2();
    cout << "---------------------" << endl;
    delete b1;
    return 0;
}

输出：

Base1()
Base2()
Member1()
Member2()
Member3()
Dervied()
---------------------
~Dervied()
~Member3()
~Member2()
~Member1()
~Base2()
~Base1()
---------------------
Base2()
Base1()
Member1()
Member2()
Member3()
Dervied()
---------------------
~Dervied()
~Member3()
~Member2()
~Member1()
~Base1()
~Base2()