class C;
class B : public std::enable_shared_from_this<B>
{
public:
 ~B(){ cout << "~B" << endl; }
 void SetPC(std::shared_ptr<C>& pc){ _pc = pc; } 

private:
 std::shared_ptr<C> _pc;
};

class C : public std::enable_shared_from_this<C>
{
public:
 ~C(){ cout << "~C" << endl; }
 void SetPB(std::shared_ptr<B>& pb){ _pb = pb; }
 
private:
 std::shared_ptr<B> _pb;
};

int main()
{
 std::shared_ptr<C> pc = std::make_shared<C>();
 std::shared_ptr<B> pb = std::make_shared<B>();
 pc->SetPB(pb);
 pb->SetPC(pc);
 return 0;
}

class C : public std::enable_shared_from_this < C >
{
public:

 ~C()
 {
  std::cout << "~C" << std::endl;
 }

 int32_t Decode(const char* data, size_t)
 {
  return 0;
 }
 void SetDecoder(std::function<int32_t(const char*, size_t)> decoder)
 {
  _decoder = decoder;
 }


private:
 std::function<int32_t(const char*, size_t)> _decoder;
};

int main()
{
 {
  std::shared_ptr<C> pc = std::make_shared<C>();
  auto decoder = std::bind(&C::Decode, pc, std::placeholders::_1, std::placeholders::_2);
  pc->SetDecoder(decoder);
 }
 // C不能正确析构 因为存在自引用
 return 0;
}

class Session : public std::enable_shared_from_this < Session >
{
public:

 ~Session()
 {
  std::cout << "~C" << std::endl;
 }

 void Start()
 {
  // 进行一些异步调用
  // 如 _socket.async_connect(..., boost::bind(&Session::ConnectCompleted, this), boost::asio::placeholders::error, ...)
 }

 void ConnectCompleted(const boost::system::err_code& err)
 {
 if(err)
 return; 

  // ... 进行处理
  // 如 _socket.async_read(..., boost::bind(&Session::ReadCompleted, this), boost::asio::placeholders::error, ...)
 }

 void Session::ReadComplete(const boost::system::error_code& err, size_t bytes_transferred)
 {
  if (err || bytes_transferred == 0)
  {
   DisConnect();
   return;
  }
 // 处理数据 继续读
 // ProcessData();
 // _socket.async_read(...)
 }

private:
 std::function<int32_t(const char*, size_t)> _decoder;
};

int main()
{
 {
  std::shared_ptr<Session> pc = std::make_shared<Session>();
  pc->Start();
 }
 return 0;
}

((A*)nullptr)->Func();

class Test
{


public:
 void Say()
 {
  std::cout << "Say Test" << std::endl;
 }

 void Set(int data)
 {
  _data = data;
 }

private:
 int _data;
};
int main()
{
 // 运行成功
 ((Test*)nullptr)->Say();
 // 运行会崩掉，尝试访问空指针所指内存(_data)
 ((Test*)nullptr)->Set(1);
 return 0;
}