C++ 虚拟析构函数导致基方法被调用

Question

我写了这个简单的例子来了解发生了什么 我希望所有逻辑都在基类中实现，并在派生类中派生特定方法，所以：

#include <thread>
#include <atomic>
#include <chrono>
#include <iostream>

class base
{
public:
    base() : stop(false) {}

    virtual ~base()
    {
        std::cout << "Destructor base\n"; 

        if( handle.joinable() )
        {
            stop = true;
            handle.join();
        }
    }

    void runThread() { handle = std::thread( worker, this ); }

    virtual void stopThread() { std::cout << "Base stopThread\n"; }

protected:
    std::atomic<bool> stop;

    std::thread handle;

    static void worker( base *me )
    {
        while( me->stop == false )
        {
            std::cout << "Working\n";
            me->stopThread(); // this one in called as derived
            std::this_thread::sleep_for( std::chrono::seconds(1) );
        }

        me->stopThread(); // this one is called as base
    }
};

class derived : public base
{
public:

    ~derived()
    {
        std::cout << "Destructor derived\n"; 
    }

private:
    void stopThread() { std::cout << "derived stopThread\n"; }
};

int main()
{
    derived der;
    der.runThread();

    std::this_thread::sleep_for( std::chrono::seconds(3) );
}

结果：

Working
derived stopThread
Working
derived stopThread
Working
derived stopThread
Destructor derived
Destructor base
Base stopThread <-- hmmm 

所以除了基本析构函数之外一切都正常 - 它调用 base::stopThread。为什么会这样？如果我把它变成纯虚拟的，我会得到一个例外。

我可以通过将析构函数移动到派生类来解决这个问题，但这不清楚，因为我希望所有逻辑都在基类中实现。

我哪里错了？

谢谢

Answer 1

虚拟方法不会分派到构造函数或析构函数中最派生的实现。原因是当base 的析构函数被调用时，derived 实例已经被销毁了。

更正式地说，正如 Quentin 在 cmets 中所说，虚方法在构造函数或析构函数内分派到实例的静态类型。