C++ 不能在已经用作变量的对象中使用成员

我有两个类，其中第一个在一个对象中实例化，该对象在类“ two”的另一个对象内使用。我遇到的问题是尝试通过第二类的对象访问第一类的对象的成员时。

我在arduino上使用这种方法来实例化一个对象，该对象将控制带有LiquidCrystal_I2C类的LCD，该对象将在实例化后立即需要参数。

示例代码：

#include <iostream>

    using namespace std;

    class A
    {
    public:
      int data;
      int state;
        A (int); // Constructor needs parameter
      void setState (int);
      int getState ();
    };

    A::A (int newdata)
    {
      data = newdata;
    }

    void A::setState (int newstate)
    {
      state = newstate;
    }

    int A::getState ()
    {
      return state;
    }

    class B
    {
    public:
      A * a;
      int aState;
        B ();
      void attachA (int);
      void printall ();
    };

    B::B ()
    {
    }

    void B::attachA (int data)
    {
      A newobj (data);
      a = &newobj;
      a->setState (data + 1);
      aState = a->getState ();
      cout << "B obj. address?: " << this <<
        ", 'A' class obj. creation with data: " << data << " B.a->getState(): " <<
        a->getState () << ", B.a->data: " << a->data << "\n";
    }

    void B::printall ()
    {
      cout << "B obj. address?: " << this << ", 'A' member class address?: " << a
        << ", B.aState: " << aState << ", B.a->getState(): " << a->
        getState () << ", B.a->data: " << a->data << "\n";
    }

    int main ()
    {
      B temp_one;
      temp_one.attachA (123);

      B temp_two;
      temp_two.attachA (345);

      temp_one.printall ();
      temp_two.printall ();

      temp_one.printall ();

      temp_one.a->setState (42);
      temp_one.printall ();

      return 0;
    }

输出：

B obj. address?: 0x7ffe088aa130, 'A' class obj. creation with data: 123 B.a->getState(): 124, B.a->data: 123                                                                       
B obj. address?: 0x7ffe088aa140, 'A' class obj. creation with data: 345 B.a->getState(): 346, B.a->data: 345                                                                       
B obj. address?: 0x7ffe088aa130, 'A' member class address?: 0x7ffe088aa108, B.aState: 124, B.a->getState(): 0, B.a->data: 4196144                                                  
B obj. address?: 0x7ffe088aa140, 'A' member class address?: 0x7ffe088aa108, B.aState: 346, B.a->getState(): 0, B.a->data: 4196144                                                  
B obj. address?: 0x7ffe088aa130, 'A' member class address?: 0x7ffe088aa108, B.aState: 124, B.a->getState(): 0, B.a->data: 4196144                                                  
B obj. address?: 0x7ffe088aa130, 'A' member class address?: 0x7ffe088aa108, B.aState: 124, B.a->getState(): 0, B.a->data: 4196144 

问题来源：stackoverflow