继承中的构造函数和析构函数的调用顺序

beyes

基类和派生类都可以包含构造函数和析构函数。我们比较关心的是，当一个派生类的对象被创建或被销毁时，这些构造函数和析构函数的调用顺序如何。

示例程序：

[C++] 纯文本查看 复制代码

#include <iostream>
using namespace std;

class base {
public:
    base() { cout << "Constructing base\n"; }
    ~base() { cout << "Desconstructing base\n"; }
};

class derived: public base {
public:
    derived() { cout << "Constructing derived\n"; }
    ~derived() { cout << "Desconstructing derived\n"; }
};

int main()
{
    derived ob;

    return 0;
}

运行输出：

$ ./inheritcon
Constructing base
Constructing derived
Desconstructing derived
Desconstructing base

从输出可以看出，base 的结构函数首先被执行，然后是 derived 的构造函数；在销毁时，先执行 derived 的析构函数，然后是 base 的析构函数。

所以，构造函数以派生的顺序进行调用，析构函数则以相反的顺序进行调用。

上述的调用规则也适用于多重继承的情况，如下程序示例：

[C++] 纯文本查看 复制代码

#include <iostream>
using namespace std;

class base1 {
public:
    base1() { cout << "Constructing base1\n"; }
    ~base1() { cout << "Destructing base1\n"; }
};

class base2 {
public:
    base2() { cout << "Constructing base2\n"; } 
    ~base2() { cout << "Destructing base2\n"; }
};

class derived: public base1, public base2 {
public:
    derived() { cout << "Constructing derived\n"; }
    ~derived() { cout << "Destructing derived\n"; }
};

int main()
{
    derived ob;

    return 0;
}

运行输出：

$ ./mulincon
Constructing base1
Constructing base2
Constructing derived
Destructing derived
Destructing base2
Destructing base1

从输出结果可以看到，构造函数是按照类 derived 定义中基类从左到右的顺序来调用基类中的构造函数，而析构函数的调用顺序则相反。