j_l_larson
Profile Answers by j_l_larson

Oct 18th, 2009

F. None of the above are entirely the right answer

You can provide a method in the base class to allow the private data to be read or written and then provide an access specifier in the derived class which allows the methods to be called. For example:

class Base {
public:
  Base() : m_nDerivable(1), m_nSecret(0) {}
  ~Base() {}
  int ReadBasePrivateData() { return m_nSecret; }
  void ModifyBasePrivateData( int n ) { m_nSecret = n; }
  int foo() { return m_nSecret + m_nDerivable; }
protected:
  int bar() { return m_nSecret + m_nDerivable; }
  int m_nDerivable;
private:
  int woozle() { return m_nSecret + m_nDerivable; } // can never be called, even with access specifiers
  int m_nSecret;
};

class PrivDeriv : private Base {
public:
  PrivDeriv() {}
  ~PrivDeriv() {}
  Base::ReadBasePrivateData; // access specifier, we are allowed to read base's private things
  Base::ModifyBasePrivateData; // access specifier, we are allowed to write over base's private things
  Base::foo; //public member allowed
  //Base::bar; //protected member can be allowed, but we selectively block it here
  //Base::woozle; //private can not be allowed - compiler error
  //int GetBasePrivateInt() { std::cout << "private derived get base private membern"; return Base::m_nSecret; } // compiler error
  int GetBaseProtectedInt() { std::cout << "private derived get base protected membern"; return Base::m_nDerivable; }
private:
};

int main( int argc, char** argv ) {
  PrivDeriv a;
  a.foo(); // allowed
  //a.bar(); // compiler error
  //a.woozle(); // compile error
  int nPrivateInt = a.ReadBasePrivateData();
  std::cout << "private int is allowed through public read method: " << nPrivateInt << "n";
  a.ModifyBasePrivateData( 10 ); // inaccessible, compiler error
  nPrivateInt = a.ReadBasePrivateData();
  std::cout << "private int has been changed through public write method: " << nPrivateInt << "n";
  return 0;
}

What should you do gain access to Private Base Class Data

prettyfox
Profile Answers by prettyfox Questions by prettyfox
Jul 23rd, 2008
4
2830

Questions by prettyfox

C++

Answer

Showing Answers 1 - 4 of 4 Answers

burraganesh
Profile Answers by burraganesh

Dec 7th, 2008

Make the derived class friend of base class

Peter_APIIT
Profile Answers by Peter_APIIT

Jul 17th, 2009

Protected Inheritance is the way to go.

tapan.gajera
Profile Answers by tapan.gajera

Jan 3rd, 2010

B. You should use a public or protected base class function.

Example:

class Base
{
private:
    int a;
public:
    Base() {a = 5;}                         //Initialize variable a;
    int AccessPrivate() {return a;} //access private member using public function
};

class Derived: public Base
{
public:
    int getData() {return AccessPrivate();} //derived class returns private data of base
};