Question

Is it possible to change the class attribute at run-time in C++ language.For example as below :

class base
{
    public:
        //public members

    private : 
        //private members
};

class derived1 : attribute base
{
    public:
        //public members
        base::<base method name> //so that it an be made accessible from the main - outside the class.

    private:
        //private members
};

can the attribute-public,private,protected be changed at runtime, dynamically?

Rgds,
softy

Answer 1

You cannot change the access modifiers of a class. End of story.

Disclaimer: There are hacks for just about everything, including this. Don’t use them.

Based on your comments in the question when asked why you want this, it looks like what you’re trying to do is control access to a class’ run-time properties based on its other run-time properties. For example, maybe a Character‘s Powers are only accessible if Character‘s Level is >= 42.

This is not a technical question about the mechanics of C++ syntax, but a business logic question. You’ll find the answer to this question in the design of your program and its algorithms — not some technical C++ trick.

Classes are often used to model things. In your case, a character in a game. Maybe this character has a level and a list of powers (which I’ll represent simply as strings).

In that case:

class Character
{
public:
  int level_;
  vector<string> powers_;
};

…is a simplistic representation of your character model. Now, if you want to control access to powers_ at run-time based on the value of level_, you can use an accessor method:

class Character
{
public:
  int level_;
  vector<string> Powers() const 
  {
    if( level_ >= 42 )
      return powers_;
    else
      return vector<string>();
  }
private:
  vector<string> powers_;
};

Now you can only get to the character’s powers if the character is of sufficiently high level.

This is still a highly simplistic example, and the above code is not production quality. However, the idea is there — when implementing your program’s business logic, your focus should be on the algorithms you write much more than the technicalities of C++, or whatever language you’re using.