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标题: 继承中的构造函数和析构函数的调用顺序 [打印本页]

作者: beyes 时间: 2011-8-27 21:08
标题: 继承中的构造函数和析构函数的调用顺序
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。

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