Friend function in c++ pdf

The friend functions should be declared and defined the following way as it. Oop purists have criticized this feature as weakening the principles of encapsulation and information hiding. For example a linkedlist class may be allowed to access private members of node. Friend function like friend class, a friend function can be given special grant to access private and protected members. But, sometimes this restriction may force programmer to write long and complex codes. Friend function is used to access the private and protected members of different classes. As we know that a class cannot access the private members of other class. A friend function is a nonmember function of class which can access the private membersdata of class. In objectoriented programming, a friend function, that is a friend of a given class, is a function. Any friend function is preceded with friend keyword.

The friend function displayrect has an access to the private member of the rectangle class object though its not a member function. To declare a function as a friend of a class, precede the function prototype in the class definition with keyword friend as follows. The friend can be a function, a function template or member function, a class or a class template where the entire class and all the members of the class are friends. They are considered to be a loophole in the object oriented programming concepts, but logical use of them can make them useful in certain cases. The duplicate function is a friend of class rectangle. In objectoriented programming, a friend function, that is a friend of a given class, is a function that is given the same access as methods to private and protected data. Friend class a friend class can access private and protected members of other class in which it is declared as friend. It is sometimes useful to allow a particular class to access private members of other class. If a function is defined as a friend function then, the private and protected data of a class can be accessed using the function. But which function has rights to access to all private and protected members variables and functions. A friend function of a class is defined outside that class scope but it has the right to access all private and protected members of the class. Functions make a program much easier to read, test and debug. A friend can be a function, function template, or member function, or a class or class template, in which case the entire class and all of its members are friends. A template friend declaration can name a member of a class template a, which can be either a member function or a member type the type must use elaboratedtypespecifier.

Declare the function with the keyword friend that is followed by return type and followed by the function name. Applying a friend function to an entire hierarchy of classes becomes awkward if an overloaded friend function is needed for every class in the hierarchy. Such declaration is only wellformed if the last component in its nestednamespecifier the name to the left of the last is a simpletemplateid. The nonmember function has to grant an access to update or access the class. We call a function a friend function if the function definition is prefixed with the friend keyword we cannot use the friend prefix outside a class, so it can only be used in the member function declaration. By declaring friends, we allow nonmember functions or member functions of other classes access to private data. Be careful when using friend functions and classes, because it allows the friend function or class to violate encapsulation. Thus, a friend function is an ordinary function or a member of another class. If we do this inside main, we get an error because they are private members and. This is needed when we want to allow a particular class to access the private and protected members of a class. A friend function is not in the scope of the class, in which it has been declared as friend. Friend function is used when we need to operate on data of. The complier knows a given function is a friend function by the use of the keyword friend.

If a function is friend function of a class, that friend function is not the actual member of the class. Since friend function is not a member of class it can not be accessed using object of the class. You can do everything you might want to do without using the friend feature. Friends are functions or classes declared with the friend keyword. It cannot be called using the object of that class. A friend function is declared inside the class with a friend keyword preceding as shown below.

The advantage of encapsulation and data hiding is that a nonmember function of the class cannot access a member data of that class. By using the keyword friend compiler knows the given function is a friend function. Define the friend function outside the class scope by taking arguments as call by reference to pass the copy of swap object. Private if data are declared as private in a class then it is accessible by the member functions of the class where they are declared. A class can allow nonmember functions and other classes to access its own private data, by making them friends. The use of functions in a program allows a program to be broken into small tasks. A friend function is a function that can access the private members of a class as though it were a member of that class. It is called in the same way as normal external function.

Create a class swap, declare three variable in it, i. When the function is declared as a friend, then it can access the private and protected data members of the class. In programming, function refers to a segment that groups code. A function can be made a friend function using keyword friend. Functions functions allow to structure programs in segments of code to perform individual tasks. Similarly a class that doesnt inherit another class cannot access its protected. Friendship and inheritance friend functions in principle, private and protected members of a class cannot be accessed from outside the same class in which they are declared.

For accessing the data, the declaration of a friend function should be made inside the body of the class can be anywhere inside class either in private or public section starting with keyword friend. Html tutorials online html, css and js editor css tutorials bootstrap 4 tutorials. A friend function is used for accessing the nonpublic members of a class. To make a function as a friend of a class, it is declared inside the class either in private or in public section with keyword friend before its declaration as follows. A friend function of the class is defined outside that class scope, but it has a right to access all the private and protected members of a class. However, situations may arise in which it is desirable to allow the explicit access to private members of class to other functions. As for the second friend function then it seems its task is to set values for an object of the type time. Write the code of the friend function in the class. Such declaration is only wellformed if the last component in its nestednamespecifier the name to the left of the last is a simpletemplateid template name followed by argument list in angle brackets that names the. Friend function is defined or declared using keyword friend before the function prototype inside the class. A friend function is a function that is not a member of a class but it can access private and protected member of the class in which it is declared as friend. A nonmember function can access the private and protected members of a class if it is declared a friend of that class.

Friend functions as we have seen in the previous sections, private and protected data or function members are normally only accessible by the code which is part of same class. Private and protected data of class can be accessed using friend function. A friend function is a function that is not a member of a class but has access to the classs private and protected members. A significant use of a friend class is for a part of a data structure, represented by a class, to provide access to the main class representing that data structure. Therefore, function duplicate is able to access the members width and height which are private of different objects of type rectangle. If we define a function as a friend function, then the protected and private data of a class can be accessed using the function. A friend class is a class that can access the private and protected members of a class in which it is declared as friend. It can be invoked like a normal function without any object. Specify the class whose private members are to be accessed in the friend function within parenthesis of the friend function. There is a detailed explanation here, but i would like to know what is the practical use of friend function. It takes objects as parameter and access their private members using object name and dot. In all other regards, the friend function is just like a normal function. Even though the prototypes for friend functions appear in the class definition, friends are not member functions. Friend functions are really an extension of the classs interface.