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Answered 2011-02-24 17:00:10

The derived class derives, or inherits, from the base class. The derived class is like a "child", and the base class, the "parent". The child class has the attributes of the parent class - its variables (those defined at the class level) and methods. Changes done to the parent class (the base class) will affect the child class (the derived class).

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What is the difference between base class and derived class in c plus plus?

There is no difference other than that a derived class inherits from a base class. That is, the derived class inherits all the public and protected members of its base class, and is a more specialised form of its base class. Thus both can be treated as if they really were base classes. The derived class can also override the virtual methods of the base class, thus allowing polymorphic behaviour without the need to know the exact type of the derived class.


Difference between single inheritance and multiple inheritance?

single inheritance A class derived from only one base class multilevel inheritance A class derived from another derived class s.gunasekaran VSBEC


What is the difference between base class pointer and derived class pointer in c plus plus?

Base class pointers can only be used to invoke base class methods, they cannot be used to invoke derived class methods unless those methods are declared virtual methods of the base. Derived class pointers, on the other hand, can be used to invoke base class methods.


What is a base class?

A base class is a class that a derived class is based on. All of the methods and attributes of the base class are included in the derived class, with the methods and attributes of the derived class either adding to the base class, or replacing (overloading) those in the base class.


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.


Constructors in derived class of c plus plus?

class base { base():m_data(0){} base(int i):m_data(i){} base(const base& b):m_data(b.m_data){} private: int m_data; }; class derived : public base { derived():base(){} // call base class default constructor derived(int i):base(i){} // call base class overloaded constructor derived(const derived& d):base(d){} // call base class copy constructor };


What is difference between virtual base class and virtual function?

A virtual function is a member method that is expected to be overridden by derived classes. A pure-virtual function is one that must be overridden in derived classes. A virtual base class is a base class that is declared virtual in its derivatives. This is commonly used when a derivative inherits from two or more base classes that each inherit from a common base class. Without virtual inheritance, the most-derived class would indirectly inherit multiple instances of the common base class. By declaring the common base class to be virtual in its derivatives, the most-derived class directly inherits the common base class, and the derivatives themselves then share that same instance.


How do you call base class method using derived class object?

If the base class method is non-private, the derived class can call the base class method implicitly. However, if the derived class overrides or overloads the method, the base class method must be called explicitly. The following demonstrates explicit calls to base class methods: #include <iostream> using namespace std; class Base { public: Base(){} void Foo(){ cout << "Base::Foo" << endl; } }; class Derived : public Base { public: Derived(){} void Foo(){ cout << "Derived::Foo" << endl; Base::Foo(); } }; int main() { Derived derived; derived.Foo(); derived.Base::Foo(); // Explicit call to base class method. return(0); } Output: Derived::Foo Base::Foo Base::Foo


What is the Difference between multilevel and multiple inheritance?

Multiple Inheritance : we can inherit more than one class in the same class. Multi-Level Inheritance: where one class can inherit only one base class and the derived class can become base class of some other class.


How many base and derived classes do you have in single inheritance?

One each. One base class and One derived class. Ex: public class A extends B { ... .. .. } Here A is the derived class and B is the base class


Does the derived class take the memory of base class in inheritance?

Yes, the derived class includes the memory of the base class. The derived class inherits everything in the base class, data and function, and provides additional data and function as needed.


What is the difference between friend function and virtual function?

A virtual function is a base class function that can be overridden by a derived class. A friend function is a non-member function that has private access to the class representation.


Is it true that a derived class inherits all the members of its base class?

False. A derived class inherits the public and protected members of its base class. Private members of the base class cannot be inherited.


What is derived class in brief?

A derived class is any class that inherits from one or more other classes, known as base classes. The derived class inherits the sum total of all public and protected members of all its base classes, including their base classes. The derived class is a more specialised form of its base classes. Any members of the base classes that are declared virtual can be overridden, such that calling the base class method directly actually invokes the derived class method, thus enabling polymorphic behaviour.


What is the difference between the direct and indirect base class?

Direct base classes are those that are specified in a derived class' inheritance declaration. Indirect base classes are those that are inherited via the direct base classes. class A{}; class B : public A{}; class C : public B{}; With respect to C, B is direct while A is indirect. With respect to B, A is direct.


How you can override base class member in derived classexplain with example?

To override a base class method you simply need to declare the base class method as being virtual. As well as creating a v-table, this also gives a visual hint to other developers that you expect the function to be overridden. The v-table ensures that all calls to the base class method are routed to the derived class method, thus ensuring objects behave polymorphically, according to their actual type, and not what we're actually pointing at. Consider the following example: #include <iostream> class base { public: virtual ~base(); virtual void PrintMe() const { std::cout << "I am a base class!" << std::endl; } }; class derived: public base { public: void PrintMe() const { std::cout << "I am a derived class!" << std::endl; } }; int main() { base b; derived d; base* pb = &d; b.PrintMe(); d.PrintMe(); pb->PrintMe(); return( 0 ); } Output: I am a base class! I am a derived class! I am a derived class! Note that although pb points to the base class instance of d, it still knows that it really is a derived class, as can be seen from the third line of output. Now try removing the virtual keyword from the base class method. The output will change as follows: Output: I am a base class! I am a derived class! I am a base class! Now your derived class thinks it is a base class. This is because the v-table no longer has no entry for that method, and therefore the call cannot be routed to the overridden derived class method. The base class method is called because that's what we're actually pointing at and the object no longer behaves polymorphically according to its actual type. Note also that if any method is declared virtual in a class, the class constructor must also be declared virtual. If you fail to do this, your classes will not be destroyed properly. The virtual keyword ensures that the most-derived class is always destroyed first, before working up the hierarchy of destructors to eventually destroy the least-derived class, the base class itself. Consider the following example without a virtual destructor: #include <iostream> class base { public: base(){ std::cout << "Base class created" << std::endl; } ~base(){ std::cout << "Base class destroyed" << std::endl; } }; class derived: public base { public: derived(){ std::cout << "Derived class created" << std::endl; } ~derived(){ std::cout << "Derived class destroyed" << std::endl; } }; int main() { derived* d = new derived(); base* b = d; delete( b ); return( 0 ); } Output: Base class created Derived class created Base class destroyed As you can see, the derived class was created but was not destroyed. We've created a memory leak: that memory cannot be recovered until the program ends. Now add the virtual keyword to the base class destructor: #include <iostream> class base { public: base(){ std::cout << "Base class created" << std::endl; } virtual ~base(){ std::cout << "Base class destroyed" << std::endl; } }; class derived: public base { public: derived(){ std::cout << "Derived class created" << std::endl; } ~derived(){ std::cout << "Derived class destroyed" << std::endl; } }; int main() { derived* d = new derived(); base* b = d; delete( b ); return( 0 ); } Output: Base class created Derived class created Derived class destroyed Base class destroyed Now we have the expected behaviour and have resolved the memory leak. Remember, if ANY method of a class is declared virtual, the destructor must also be declared virtual. Note that although derived classes need not use the virtual keyword in front of overrides (it is implied by the base class), there is no harm in explicitly declaring them as such, if only to give a visual hint that the methods are expected to be overridden by derivatives of the derivative (multi-level inheritance).


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 derived class make a public base function private true or false?

True. A derived class can make a public base function private. The derived function is private, within the derived class, but public in other contexts.


What do you mean by multiple inheritance and multileval inheritance in cplus plus?

Multiple inheritance relates to a class that is directly derived from two or more base classes. The derive class directly inherits the sum of all the public and protected members of all base classes. Multi-level inheritance relates to a class that derives from a base class which is itself derived from another base class. The least-derived base class is indirectly inherited by the most-derived class. That is; the most-derived class inherits the sum of all the public and protected members of all its base classes (whether directly or indirectly. Multiple inheritance and multi-level inheritance can also be combined. This can lead to ambiguity issues if two or more base classes are derived from a common base class. To avoid this problem, the common base class can be inherited virtually in the derived base classes, thus the most-derived class will inherit directly from the common base class, and the base classes will share the same instance of the common base class.


Which base class member functions are not inherited by a derived class?

Derived classes only inherit the protected and public members of their base classes. Private member functions cannot be inherited by a derived class.


When the concept of method overriding is necessary?

concept of overriding is very important as due to overriding the derived class can use the function of the base class! when the function has same name and prototype in both the classes(base and derived) then the derived class can use the funtion of base class!


What are Public and Private inheritance in c plus plus?

Public, protected and private inheritance determine how the public and protected base class members are inherited by the derived class. Private members are never inherited and are therefore unaffected by the type of inheritance (they remain private to the base class). The following table summarises how inheritance affects accessibility of base class members with respect to the derived class: public inheritanceprotected inheritanceprivate inheritancepublic member of base classpublic member of derived classprotected member of derived classprivate member of derived classprotected member of base classprotected member of derived classprotected member of derived classprivate member of derived classprivate member of base classprivate member of base classprivate member of base classprivate member of base class Note that accessibility to individual public and protected base class members can be overridden within the derived class, regardless of the type of inheritance specified.


Can a derived class access a function of its base class?

Yes, provided the function is public or protected. However, if the derived class overrides or overloads the function, the base class function (including all its overloads), are hidden from the derived class. To avoid this, non-private base class functions should be declared virtual.


What is the Practical application of a derived class object stored in base class pointer?

If you have base class derived object pointing by base class pointer, then you have the power of run time polymorphism in your hand, which gives you the ability to call the derived class implementation of the virtual member function. If we declare the member function as virtual in base class which needs to overridden in derived class, then you can decide at run time which implementation will be called at run time.


What is a derived class in c plus plus?

A derived class is any class that inherits from another class (known as a base class). Derived classes can inherit from several base classes (multiple inheritance). Base classes may themselves be derived from other classes. Each derivative expands upon the functionality of its base class, making it more specialised. Derived classes inherit all the public and protected members of their base classes, except the constructors. Friends of base classes are not inherited either. An example of class inheritance declaration: class myDerivedClass : public myBaseClass { public: myDerivedClass(); };


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