Friend function in c++ pdf

Html tutorials online html, css and js editor css tutorials bootstrap 4 tutorials. It is called in the same way as normal external function. A class can allow nonmember functions and other classes to access its own private data, by making them friends. A friend function is used for accessing the nonpublic members of a class. Define the friend function outside the class scope by taking arguments as call by reference to pass the copy of swap object. When the function is declared as a friend, then it can access the private and protected data members of the class. 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. A friend function is a function that is not a member of a class but has access to the classs private and protected members. The use of functions in a program allows a program to be broken into small tasks. In objectoriented programming, a friend function, that is a friend of a given class, is a function. The friend function displayrect has an access to the private member of the rectangle class object though its not a member function. 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.

But which function has rights to access to all private and protected members variables and functions. However, situations may arise in which it is desirable to allow the explicit access to private members of class to other functions. The complier knows a given function is a friend function by the use of the keyword friend. 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.

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. A friend function is a nonmember function of class which can access the private membersdata of class. Functions functions allow to structure programs in segments of code to perform individual tasks. You can do everything you might want to do without using the friend feature. 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. If we define a function as a friend function, then the protected and private data of a class can be accessed using the function. The advantage of encapsulation and data hiding is that a nonmember function of the class cannot access a member data of that class. In programming, function refers to a segment that groups code. Friend function like friend class, a friend function can be given special grant to access private and protected members. 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 functions should be declared and defined the following way as it. Private and protected data of class can be accessed using friend function.

It can be invoked like a normal function without any object. It is sometimes useful to allow a particular class to access private members of other class. Therefore, function duplicate is able to access the members width and height which are private of different objects of type rectangle. Such declaration is only wellformed if the last component in its nestednamespecifier the name to the left of the last is a simpletemplateid. For example a linkedlist class may be allowed to access private members of node. By using the keyword friend compiler knows the given function is a friend function. We will first go through the theory of what is a friend function. A friend function can also be used for function overloading. The nonmember function has to grant an access to update or access the class.

Any friend function is preceded with friend keyword. Thus, a friend function is an ordinary function or a member of another class. How i can decide when i should go with a friend function rather than a member function. It cannot be called using the object of that class.

Friend function is used when we need to operate on data of. 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. As for the second friend function then it seems its task is to set values for an object of the type time. The duplicate function is a friend of class rectangle. 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. If a function is defined as a friend function then, the private and protected data of a class can be accessed using the function. Declare the function with the keyword friend that is followed by return type and followed by the function name. It takes objects as parameter and access their private members using object name and dot. Friends are functions or classes declared with the friend keyword. Oop purists have criticized this feature as weakening the principles of encapsulation and information hiding. If a function is friend function of a class, that friend function is not the actual member of the class. A nonmember function can access the private and protected members of a class if it is declared a friend of that class. Specify the class whose private members are to be accessed in the friend function within parenthesis of the friend function.

Functions make a program much easier to read, test and debug. 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. A friend function is a function that can access the private members of a class as though it were a member of that class. But, sometimes this restriction may force programmer to write long and complex codes. 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. 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. Friend functions are really an extension of the classs interface.

Write the code of the friend function in the class. Friend function is used to access the private and protected members of different classes. Be careful when using friend functions and classes, because it allows the friend function or class to violate encapsulation. 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. A friend class is a class that can access the private and protected members of a class in which it is declared as friend. 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. Create a class swap, declare three variable in it, i. Even though the prototypes for friend functions appear in the class definition, friends are not member functions. A friend function is declared inside the class with a friend keyword preceding as shown below. A function can be made a friend function using keyword friend. 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.

This is needed when we want to allow a particular class to access the private and protected members of a class. 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. A friend function is not in the scope of the class, in which it has been declared as friend. 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. Since friend function is not a member of class it can not be accessed using object of the 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. As we know that a class cannot access the private members of other class. By declaring friends, we allow nonmember functions or member functions of other classes access to private data. If we do this inside main, we get an error because they are private members and. Similarly a class that doesnt inherit another class cannot access its protected. There is a detailed explanation here, but i would like to know what is the practical use of friend function. In all other regards, the friend function is just like a normal function.