c++中的父子关系

考虑下面的c++代码

class B;
class A{
private:
    B* mB;
};
class B{
private:
    doSomethingImportant();
};

我们有一个对象a，它包含对象B，父对象是a，子对象是B。现在，如果我想让a让B执行doSomethingImportant()，我认为将a添加为B的朋友是唯一的方法。

类B中的friend class A，这将使A的函数能够访问B的私有函数。

我发现这种方法有点奇怪，因为在Data_Hiding概念中创建了一个漏洞。是否有更好的方法在对象之间建立父子关系?或者这是最好的方法?

添加我对这个问题的实际动机

class elevator{
private:
    //The Lift box the elevator controls
    liftboxControlUnit & mLiftBoxCtrlUnit;   
    //constructor
    elevator(int Level=1, int NoOfBanks =1 );
    //Destructor
    ~elevator();
    //Triggers the search to move to the next floor if required 
    void moveLiftToNext();
public:
    //Adds request to the queue
    void addRequest(int FloorNumber){
    //Add the request to the queue. The single button outside the elevator door
    mLiftBoxCtrlUnit.addRequest(FloorNumber);
    }
    //For Emergency. Should be accessible to everyone !
    void setEmergency();
    void unsetEmergency();
};
typedef enum Direction{
    UP,
    DOWN
}direction;
class liftboxControlUnit{
private:
    //The request for various floors
    set<int> mRequestQueue;
    //The various banks for the whole system
    vector<Bank> mBanks;
    //The total number of levels. Remains the same for one building
    const int mTotalLevel;
    //Instruction to move the box to certain level
    void processRequest(){
        //Do the logic to move the box.
    }
    //can passed to the elevator
    void addRequest(int x){
        mRequestQueue.insert(x);
    }
    //Can be set by elevator class
    void setEmergency(){
        //Do the required 
        //Set Emergency on all Banks
    }
    void unsetEmergency(){
        //UnsetEmegency on all banks
    }
    void emergencyListener(){
        //Listen to all the banks if emergency has been set
    }
    void BankFreeListener(){
        //Listen to the banks if any is free
        //If so then
        processRequest();
    }
public:
    //Constructor
    liftboxControlUnit(int TotalLevels, int NoOfBanks): mTotalLevel(TotalLevels){
        for(int i=0 ; i lessthan NoOfBanks; ++ i)
            mBanks.push_back(Bank(0,UP));
    }    
    friend class elevator;
};
class Bank{
private:
    //The dailpad inside the bank
    dailpad & mpad;
    //Current Location
    int mPresentLevel;
    //Current direction of movement
    direction mDirection;
    //Currently moving
    bool mEngaged;
    //Manipulate the bank
    void move(int NoOfMoves){
        setEngaged();
        //Move the elevator
        unsetEngaged();    
    }
    //getters
    int getPresentLevel() const;
    int getDirection() const;
    //setters
    void setPresentLevel(int);
    void setDirection(direction);
    //Manipulate the engaged flag
    bool isEngaged() const;
    bool setEngaged();
    bool unsetEngaged();
    //For emergency
    void reset();
    //Dailpad Listener
    void dailpadListener(){
    }

public:
    Bank(int StartingLevel, direction Direction): mPresentLevel(StartingLevel),
            mDirection(Direction),
            mEngaged(false),
            mpad()
    {
    }
    //For emergency . Should be available for all.
    void SetEmergency();
    void UnsetEmergency();
    bool isEmergency();
    friend class liftboxControlUnit;
};

class dailpad{
private:
    //Some DS to represent the state . probably a 2D Array.
    void renderDisplay();
public:
    //Constructor
    dailpad();
    void getCommand(int x){
        //Depending on the value we can do the following
        //Make necessary changes to the display
        renderDisplay();
    }
    friend class Bank;
};