What are access specifiers Should I inherit with private protected or public

Question

I am confused about the meaning of access modifiers with respect to inheritance  What is the difference between inheritance involving the private  protected and public keywords

User · Answer

The explanation from Scott Meyers in Effective C++ might help understand when to use them:

Public inheritance should model "is-a relationship," whereas private inheritance should be used for "is-implemented-in-terms-of" - so you don't have to adhere to the interface of the superclass, you're just reusing the implementation.

User · Answer

what are Access Specifiers   There are 3 access specifiers for a class struct Union in C    These access specifiers define how the members of the class can be accessed  Of course  any member of a class is accessible within that class Inside any member function of that same class   Moving ahead to type of access specifiers  they are     Public - The members declared as Public are accessible from outside the Class through an object of the class     Protected - The members declared as Protected are accessible from outside the class BUT only in a class derived from it     Private - These members are only accessible from within the class  No outside Access is allowed   An Source Code Example   class MyClass       public          int a      protected          int b      private          int c      int main         MyClass obj      obj a   10        Allowed     obj b   20        Not Allowed  gives compiler error     obj c   30        Not Allowed  gives compiler error       Inheritance and Access Specifiers  Inheritance in C   can be one of the following types      Private Inheritance   Public Inheritance   Protected inheritance     Here are the member access rules with respect to each of these        First and most important rule Private members of a class are never accessible from anywhere except the members of the same class      Public Inheritance      All Public members of the Base Class become Public Members of the derived class  amp    All Protected members of the Base Class become Protected Members of the Derived Class      i e  No change in the Access of the members  The access rules we discussed before are further then applied to these members     Code Example     Class Base       public          int a      protected          int b      private          int c      class Derived public Base       void doSomething                 a   10     Allowed          b   20     Allowed         c   30     Not Allowed  Compiler Error           int main         Derived obj      obj a   10     Allowed     obj b   20     Not Allowed  Compiler Error     obj c   30     Not Allowed  Compiler Error      Private Inheritance      All Public members of the Base Class become Private Members of the Derived class  amp    All Protected members of the Base Class become Private Members of the Derived Class    An code Example     Class Base       public        int a      protected        int b      private        int c      class Derived private Base     Not mentioning private is OK because for classes it  defaults to private        void doSomething                 a   10     Allowed          b   20     Allowed         c   30     Not Allowed  Compiler Error           class Derived2 public Derived       void doSomethingMore                 a   10     Not Allowed  Compiler Error  a is private member of Derived now         b   20     Not Allowed  Compiler Error  b is private member of Derived now         c   30     Not Allowed  Compiler Error           int main         Derived obj      obj a   10     Not Allowed  Compiler Error     obj b   20     Not Allowed  Compiler Error     obj c   30     Not Allowed  Compiler Error      Protected Inheritance      All Public members of the Base Class become Protected Members of the derived class  amp    All Protected members of the Base Class become Protected Members of the Derived Class      A Code Example   Class Base       public          int a      protected          int b      private          int c      class Derived protected Base         void doSomething                 a   10     Allowed          b   20     Allowed         c   30     Not Allowed  Compiler Error           class Derived2 public Derived       void doSomethingMore                 a   10     Allowed  a is protected member inside Derived  amp  Derived2 is public derivation from Derived  a is now protected member of Derived2         b   20     Allowed  b is protected member inside Derived  amp  Derived2 is public derivation from Derived  b is now protected member of Derived2         c   30     Not Allowed  Compiler Error           int main         Derived obj      obj a   10     Not Allowed  Compiler Error     obj b   20     Not Allowed  Compiler Error     obj c   30     Not Allowed  Compiler Error     Remember the same access rules apply to the classes and members down the inheritance hierarchy      Important points to note   - Access Specification is per-Class not per-Object  Note that the access specification C   work on per-Class basis and not per-object basis  A good example of this is that in a copy constructor or Copy Assignment operator function  all the members of the object being passed can be accessed   - A Derived class can only access members of its own Base class  Consider the following code example   class Myclass        protected          int x        class derived   public Myclass       public           void f  Myclass amp  obj                           obj x   5                  int main         return 0      It gives an compilation error           prog cpp 4  error     int Myclass  x    is protected   Because the derived class can only access members of its own Base Class  Note that the object obj being passed here is no way related to the derived class function in which it is being accessed  it is an altogether different object and hence derived member function cannot access its members     What is a friend  How does friend affect access specification rules   You can declare a function or class as friend of another class  When you do so the access specification rules do not apply to the friended class function  The class or function can access all the members of that particular class       So do friends break Encapsulation    No they don t  On the contrary they enhance Encapsulation   friendship is used to indicate a intentional strong coupling between two entities  If there exists a special relationship between two entities such that one needs access to others private or protected members but You do not want everyone to have access by using the public access specifier then you should use friendship

[c++] What are access specifiers? Should I inherit with private, protected or public?

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