Mar 07, 2016 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. If you want two classes to be friends of each other, both must declare the other as a friend. It does not matter whether you declare the friend function in the private or public section of the class. A function is a block of code that performs a specific task. This language is similar to the c language, but it has additional features than c. Zainab mahmood fadhil page 1 friend function sometimes we need a nonmember function that has full access to the private data of a class. It is called in the same way as normal external function is called. A friend function is declared inside the class with a friend keyword preceding as shown below.
A non member function has access to all the private and protected members of a class. When the function is declared as a friend, then it can access the private and protected data members of the class. A friend can be a function, function template, or member function. Private member can be accessed inside friend function using object name and dot. Agetter, this makes the function useless outside of c. If a function is defined as a friend function then, the private and protected data of a class can be accessed using the function the complier knows a given function is a friend function by the use of the keyword friend 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. Friend functions are not a part of the class and are external. Private and protected data or function members are normally only accessible by the code which is part of same class. So, it can access all the private and protected members of the class. A function can be made a friend function using keyword friend.
So, the private data can be accessed from this function. Because operator example shows a point class and a friend function, changeprivate. Friend function is used when we need to operate on data of. Friend function private members and functions of the class are not accessible outside the class until the concepts of friend function came. A friend function can be friendly to 2 or more classes.
However, situations may arise in which it is desirable to allow the explicit access to private members of class to other functions. Be careful when using friend functions and classes, because it allows the friend function or class to violate encapsulation. But which function has rights to access to all private and protected members variables and functions. Normally private and protected members of a class could not be accessed from outside the class but in some cases the program may have to access the private or protected variables to perform the functionality. By using the keyword friend compiler knows the given function is a friend function. A non member function has access to all the private and protected members of a class 4. Simulating the fact function recursivefactorial enter n. You will find examples related to functions in this article. One of the important concepts of oop is data hiding, i. In our example, rectangle is considered a friend class by square, but square is not considered a friend by rectangle. If the friend class or class template specializationinstantiation has nested classes. 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. All c programs are written using functions to improve reusability, understandability and to keep track on them. The functions can be defined somewhere in the program just like a normal function but friend function is defined outside the class but it can still access all the private and protected members of the class.
Feb 11, 2017 a friend function is a nonmember function of the class that has been granted access to all private members of the class. In main method, for example, an exception will be thrown, if you try to get instanceofa there. However, situations may arise in which it is desirable to allow the explicit access to private members of one class to other functions. 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. I was struggling with the issue described in this question declaring a template function as a friend of a template class, and i believe the 2nd answer is what i want to do forward declare the te. The x is an object of the class friendcl function, which is declared in the friend function to pass arguments. In such case you have two options b create a function to perform that task, and just call it every time you need to perform that task. Friend function will be defined outside the class without specifying the class name. The object itself acts as a source and destination object. To understand examples in this page, you should have the knowledge of the following topics. Therefore, the member functions of rectangle can access the protected and private members of square but not the other way around. A friend can be a function, function template, or member function, or a class or class.
Since friend function is not a member of class it can not be accessed using object of the class. It is a type of a function which has the permission to access the private and protected members of a class in which this function is declared by a friend keyword. Private and protected data of a class can be accessed by making a function as a friend function of the class. A friend declaration constitutes a use of the template, not a declaration of the template. As an example, consider the factorial function, which can be defined in either of the following ways. Any friend function is preceded with friend keyword. In the above example, we could have made display as a member function of the class instead of declaring it as a friend function to the class. A friend function is a nonmember function of the class that has been granted access to all private members of the class. Friend function must be declare in all the classes from which we need to access private or protected members.
Friend function cannot call with the help of object of that class, it is call by using normal c function. Suppose you are building an application in c language and in one of your program, you need to perform a same task more than once. We will first go through the theory of what is a friend function. You can learn below concepts of c functions in this section in detail. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the. If a function is defined as a friend function then, the private and protected data of a class can be accessed using the function the complier knows a given function is a friend function by the use of the keyword friend. The friend function has access to the private data member of the point object it receives as a parameter. The nonmember function has to grant an access to update or access the class. The operator function is defined as a friend function. Also, in other situations we would like many classes to share a particular function. It cant be called using object like other member function. 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. In this situation friend function plays a major role.
Now it is allowed and it will work too, because you call it inside the constructor of c. The declaration of friend function should be made inside the body of class can be anywhere inside class either in private or. Even though the prototypes for friend functions appear in the class definition, are not member functions. We simply declare the function within the class by a prefixing its declaration with keyword friend. An overloaded leftshift operator function, which is often a friend, is needed to achieve seamless streaming capabilities. Friend function is defined by its keyword friend private and protected data of class can be accessed using friend function. What are some situations when a friend function can be useful. For example a linkedlist class may be allowed to access private members of node. Friend function is defined or declared using keyword friend before the function prototype inside the class. The declaration of friend function is one inside the class in private or public part and a function can be declared as friend function in any number of classes. Friend function has privileges to access all private and protected members variables and functions of the class. Following are some important points about friend functions and classes. 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.
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. Though this example gives you what idea about the concept of friend function. Jun 23, 2016 a virtual function is a member function that you expect to be redefined in derived classes. In this article, you will find a list of c programs to sharpen your knowledge of functions and recursion. This is to say, it has special privileges to access to the classs private and protected members. Generally, friend function can take object as a argument. Friend function like friend class, a friend function. Oop purists have criticized this feature as weakening the principles of encapsulation and information hiding. 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 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.
If a function is friend function of a class, that friend function is not the actual member of the class. In the above declaration, the friend function is preceded by the keyword friend. The function is marked internal to minimize its exposure, but the argument should also act as a form of selfdocumentation that it isnt meant for common use. A friend is one who has access to all yourprivate stuff 3. The function definition does not use either the keyword friend or scope resolution operator. In the above example the class sum is a friend function for the class friendcl. It can take multiple objects as parameter as required. Friend function must be declared with friend keyword. You can do everything you might want to do without using the friend feature. Here temp is a friend function of the class temperature.
A function that accesses private members of a class but is not itself a member of class is called friend function. A true template declaration must precede the friend declaration. Oct 20, 2018 a friend function is one that forms part of the interface to a class, but for one reason or another cant be a member of the class. Finally, if class a is a friend of b, and b is a friend of c, that does not mean a is a friend of c.
The keyword friend or scope access operator must not precede the definition of the friend function. 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. A large c program is divided into basic building blocks called c function. But friend function to the class can access the private members. Here, friend function func is declared inside distance class.
In such situations, we define the function as a friend function with these classes. 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. I was struggling with the issue described in this question declaring a template function as a friend of a template class, and i believe the 2nd answer is what i want to do forward declare the template function, then name a specialization as a friend. Learn the syntax, implementation, example, charactersitics. What is the difference between friend function and normal. A friend function is not in the scope of the class, in which it has been declared as friend. It takes objects as parameter and access their private members using object name and dot. The declaration of friend function should be made inside the body of class can be. The friend function can access private and protected data members. The complier knows a given function is a friend function by the use of the keyword friend. It is sometimes useful to allow a particular class to access private members of other class. Friend class a friend class can access private and protected members of other class in which it is declared as friend. Friendships are never corresponded unless specified. If we define a function as a friend function, then the protected and private data of a class can be accessed using the function.
Even though the prototypes for friend functions appear in the class definition, friends are not member functions. C functions are basic building blocks in a program. Friend function will be invoked like normal function, without any object. So this can use even the private variables a,b of the class friendcl. A function is a block of statements that performs a specific task. It function makes the private members and function to be accessed outside the class. A canonical example is that of types that can be printed to output streams e. To declare a function as a friend of a class, precede the function prototype in the class definition with keyword friend as follows.