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Base class should no knowledge about derived classes.
The "private" modifier on a data member means private to the class which defined it. Base class cannot directly reference/access the private data member of the derived class, and the derived classes cannot access the private data member defined in the base class.
Either way the accessing the private data member should be done via properties or getters
What else can I help you with?
What is containership in oops concept?
In container class we can only access the public part of base class. For accessing of private and protected part of base class we use friend functions.
How can the base class data be accessed from database directly using derived class?
In order to access a base class member the base class member must be declared protected or public. Private data is only accessible to members of the same class and to friends of the class. I'm not entirely sure what you mean by accessing from a database. A derived class does not require a database in order to access its base class members, it only requires protected access at the very least. Note that although you can declare derived classes to be friends of their base classes and thus allow private access, it would be an unusual design since base classes should never know anything about any of their derivatives.
What do you mean by protected derivation of a sub class from base class?
When you derive a class (the sub-class) from a base class using protected access, all public members of the base class become protected members of the derived class, while protected members of the base class will remain protected. Private members are never inherited so they remain private to the base class. By contrast, if you use public inheritance, the public members of the base class remain public to the derived class, while protected members of the base class remain protected in the derived class. If you use private inheritance, both the public and protected members of the base class become private to the derived class. Note that accessibility cannot be increased, only reduced or left the same. That is, a protected member of a base class cannot be inherited as a public member of a derived class -- it can only be declared private or remain protected. Note also that accessibility is viewed from outside of the derived class. That is, all members of a base class other than the private members are inherited by the derived class and are therefore fully accessible to the derived class. But from outside of the derived class, all base class accessibility is determined by the access specified by the type of inheritance.
Can a friend function of derived class access private data of base class?
In some computer languages it is possible to do so, but I would not even think or design any application in this way. A base class SHOULD NEVER know what the derived classes are. Perhaps it was created by generalizing some classes. Even at that point, this new base class should have no knowledge of the derived classes whatsoever. To do a good OO design, the base class should have a method like getPrivatePartOfDerivedClass() as abstract, then force the derived class to provide the implementation of this method.
Can you access a protected member from a Sub class outside the package of its Base class?
Protected members of a class are only accessible to its subclasses and to friends of the class or its subclasses. However, if a subclass changes the access to private, only the subclass and its friends have access but this does not affect the access rights of its ancestors or their friends.
What specifies private access modifier and private base class?
A private variable is something that is not visible outside the class. A private class is one that cannot be inherited
Difference bitween various visibility modes used c plus plus?
By visibility I assume you mean member accessibility. C++ uses three levels of accessibility: private, protected and public. Private members are only accessible to the class itself and friends of the class. Protected members are the same as private members except derived classes also have access. Public members are fully accessible. With regards inheritance, base class members with greater access than that specified are reduced to the specified access in the derived class. Thus public inheritance has no effect on base class member access. Protected inheritance reduces public members of the base class to protected members of the derived class. Private inheritance reduces both public and protected members of the base class to private members of the derived class. Private members of the base class are never inherited, thus they always remain private to the base class. Note that access to base class members can never be increased through inheritance, only reduced or kept the same. However, as well as defining an overall inheritance access, you can also specify member-wise inheritance access. Thus you could use public inheritance overall, but specify certain public members of the base class to be protected or private in the derived class and/or certain protected members of the base class to be private members of the derived class.
What is containership in oops concept?
In container class we can only access the public part of base class. For accessing of private and protected part of base class we use friend functions.
Which access label allows the variables to be accessible in both the current assembly and by any classes derived from the base class?
Protected access. This is the same as private access except that derivatives can also gain access. However, in order to preserve encapsulation of the base class, only its private member methods should be granted protected access (and only where that access is necessary). Private data members should never be elevated to protected access.
How can the base class data be accessed from database directly using derived class?
In order to access a base class member the base class member must be declared protected or public. Private data is only accessible to members of the same class and to friends of the class. I'm not entirely sure what you mean by accessing from a database. A derived class does not require a database in order to access its base class members, it only requires protected access at the very least. Note that although you can declare derived classes to be friends of their base classes and thus allow private access, it would be an unusual design since base classes should never know anything about any of their derivatives.
What do you mean by protected derivation of a sub class from base class?
When you derive a class (the sub-class) from a base class using protected access, all public members of the base class become protected members of the derived class, while protected members of the base class will remain protected. Private members are never inherited so they remain private to the base class. By contrast, if you use public inheritance, the public members of the base class remain public to the derived class, while protected members of the base class remain protected in the derived class. If you use private inheritance, both the public and protected members of the base class become private to the derived class. Note that accessibility cannot be increased, only reduced or left the same. That is, a protected member of a base class cannot be inherited as a public member of a derived class -- it can only be declared private or remain protected. Note also that accessibility is viewed from outside of the derived class. That is, all members of a base class other than the private members are inherited by the derived class and are therefore fully accessible to the derived class. But from outside of the derived class, all base class accessibility is determined by the access specified by the type of inheritance.
Can a friend function of derived class access private data of base class?
In some computer languages it is possible to do so, but I would not even think or design any application in this way. A base class SHOULD NEVER know what the derived classes are. Perhaps it was created by generalizing some classes. Even at that point, this new base class should have no knowledge of the derived classes whatsoever. To do a good OO design, the base class should have a method like getPrivatePartOfDerivedClass() as abstract, then force the derived class to provide the implementation of this method.
Can you access a protected member from a Sub class outside the package of its Base class?
Protected members of a class are only accessible to its subclasses and to friends of the class or its subclasses. However, if a subclass changes the access to private, only the subclass and its friends have access but this does not affect the access rights of its ancestors or their friends.
What is visibility mode what are the different inheritance visibility modes support by c plus plus?
There is no such thing as visibility mode in C++. Visibility is a function of information hiding but that relates to the way in which implementation details can be obfuscated within binary executables and libraries where only the interface need be exposed in a plain-text header file. This has nothing whatsoever to do with object oriented programming since information hiding is also possible in C. You probably meant access specifiers. There are three levels: private, protected and public. Private access limits access to the class and to friends of the class. Protected is the same as private but extends access to derivatives of the class. Public access imposes no limits. In terms of inheritance, the specified access level determines the accessibility of the protected and public members of the base class (private members are never inherited and will always remain private to the base class). in essence, members with access greater than the specified inheritance are reduced to the specified access. Thus if you specify protected inheritance, all public members of the base class become protected members of the derivative, while private inheritance reduces all public and protected members to private access. You may also reduce access to specific base class members simply be redeclaring them with the appropriate access.
How can a base class protect derived classes so that changes to the base class will not affect them explain with example?
In order for a base class to protect derived classes, so that changes to the base class do not affect the derived classes, you must make sure that the public interface exposed by the base class does not change when the implementation of those public methods do change. You can also prevent inadvertant access to the base class attributes from the derived class, by making them private. class base { public: base(...) {...}; /* constructor */ base~(...) {...}; /* destructor */ method(...) {...}; /* other public methods */ private: ... etc. } class child : base { public: ... private: ... } So long as the calling sequence and functionality (interface) of the base class public methods do not change, the implementation of those public methods can change, and the private methods and attributes can change, without impacting any child class.
Why private data members or functions are not inherited?
Because that's what private means. Private data members or functions are intended to be usable only in the base class, and the inheriting class can only access protected or public members or functions.
What is a public class?
A public class is a base class declared with public inheritance: class base { // ... }; class derived : public base { // ... }; In the above example, base is a public class of derived, thus derived is regarded as being a type of base. The derived class inherits all the public and protected methods of its base. Protected methods are accessible to the derived class, its derivatives and their friends. If base were declared protected, its public methods become protected methods of derived. The base class is then an implementation detail of derived; only members of derived, its derivatives and their friends can treat derived as being a type of base. If declared private, the public and protected methods of base become private methods of derived. The base class is then an implementation detail of derived; only members of derived and its friends can treat derived as a type of base.
