为什么要在 C++ 中为抽象类声明虚拟析构函数? [英] Why should I declare a virtual destructor for an abstract class in C++?

问题描述

我知道在 C++ 中为基类声明虚拟析构函数是一种很好的做法，但是即使对于用作接口的抽象类，声明 virtual 析构函数总是很重要吗?请提供一些原因和示例.

I know it is a good practice to declare virtual destructors for base classes in C++, but is it always important to declare virtual destructors even for abstract classes that function as interfaces? Please provide some reasons and examples why.

推荐答案

对于界面来说，这一点更为重要.你的类的任何用户都可能持有一个指向接口的指针，而不是一个指向具体实现的指针.当他们来删除它时，如果析构函数是非虚拟的，他们将调用接口的析构函数(或编译器提供的默认值，如果您没有指定)，而不是派生类的析构函数.即时内存泄漏.

It's even more important for an interface. Any user of your class will probably hold a pointer to the interface, not a pointer to the concrete implementation. When they come to delete it, if the destructor is non-virtual, they will call the interface's destructor (or the compiler-provided default, if you didn't specify one), not the derived class's destructor. Instant memory leak.

例如

class Interface
{
   virtual void doSomething() = 0;
};

class Derived : public Interface
{
   Derived();
   ~Derived() 
   {
      // Do some important cleanup...
   }
};

void myFunc(void)
{
   Interface* p = new Derived();
   // The behaviour of the next line is undefined. It probably 
   // calls Interface::~Interface, not Derived::~Derived
   delete p; 
}

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