问在基类/派生类中称为C++的纯虚函数

EN

class Base {
public:
  Base();
  virtual ~Base();
protected:
  virtual on_next_item(std::string& item) = 0;
private:
    void read_loop();
};

class Derived : public Base {
public:
  Derived();
  virtual ~Derived();
protected:
  void on_next_item(std::string& item) override;
};

while (running.load())
{
  string item = read();
  if (running.load())
  {
    on_text_item(item);
  }
}

#include <atomic>
#include <boost/thread/thread.hpp>
#include <boost/chrono.hpp>
#include <iostream>

class Base
{
public:
  Base() : running(true)
  {
    readerThread = new boost::thread(&Base::read_loop, this);
  }

  virtual ~Base()
  {
    running = false;

    delete readerThread;
    readerThread = nullptr;
  }

protected:
  virtual void on_next_item(std::string &item) = 0;

private:
  boost::thread *readerThread;

  void read_loop()
  {
    std::string element = "Element";
    while (running.load())
    {
      boost::this_thread::sleep_for(boost::chrono::milliseconds(2));
      on_next_item(element);
    }
  }

  std::atomic_bool running;
};

class Derived : public Base
{
public:
  Derived() : Base()
  {
  }

  virtual ~Derived()
  {
  }

protected:
  virtual void on_next_item(std::string &item)
  {
    std::cout << "On Next Item " << item << std::endl;
  }
};

void constAndDestruct()
{
  Derived d;
  boost::this_thread::sleep_for(boost::chrono::seconds(2));
}

int main(int argc, char **argv)
{

  constAndDestruct();
  boost::this_thread::sleep_for(boost::chrono::seconds(2));
}