[C++ rudiment]虚析构函数
C++的多态性是通过虚函数来实现的,虚函数的出现使得动态链接成为可能。
基于构造函数的特点,不能将构造函数定义为虚函数,但可以将析构函数定义为虚函数。当派生类的对象从内存中撤销时,会先调用派生类的析构函数,然后自动调用基类的析构函数,如此看来析构函数也没有必要定义为虚函数。但是考虑如下这种情况,如果使用基类指针指向派生类的对象,而这个派生类对象恰好是用new运算创建的,这种情况下会如何呢?当程序使用delete运算撤销派生类对象时,这时只会调用基类的析构函数,而没有调用派生类的析构函数。如果使用的是虚析构函数的话,就不一样了,所以定义虚析构函数有时候还是很有必要的。下面这段程序就说明了上面的问题:
没有定义虚析构函数时,code如下:
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输出的是A::destructor
这说明delete pA只是调用了基类A的析构函数,而没有调用子类B的析构函数,这不是我们所想要的。
而把基类A的析构函数定义为虚函数后,就可以达到了我们所想要的效果了。code如下:
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输出如下:
B::destrutor
A::destrutor
我没有什么雄心壮志,我只想给自己和关心自己的家人和朋友一个交代,仅此而已。