Classes and objects in c++
- 2. Key Point An object or class contains the data and the functions that operate on that data. Objects are similar to structs but contain functions, as well. MRI 2
- 3. Limitations of Procedural Programming • If the data structures change, many functions must also be changed • Programs that are based on complex function hierarchies are: –difficult to understand and maintain –difficult to modify and extend –easy to break MRI 3
- 4. Class class: like a struct (allows bundling of related variables), but variables and functions in the class can have different properties than in a struct A class is a building block of OOP. It is the way to bind the data and its logically related functions together. An abstract data type that can be treated like any other built in data type. Class definition: Class head class name_of_class. Class body { data members; member functions; }; MRI 4
- 5. Class Features Class name must start with an uppercase letter. If class name is made of more than one word, then first letter of each word must be in uppercase. Classes contain, data members and member functions, and the access of these data members and variable depends on the access specifiers (discussed in next section). Class's member functions can be defined inside the class definition or outside the class definition. Class in C++ are similar to structures in C, the only difference being, class defaults to private access control, where as structure defaults to public. All the features of OOPS, revolve around classes in C++. Inheritance, Encapsulation, Abstraction etc. Objects of class holds separate copies of data members. We can create as many objects of a class as we need. Classes do posses more characteristics, like we can create abstract classes, immutable classes, all this we will study later. MRI 5
- 6. Object Object is an instance of a class, which holds the data variables declared in class and the member functions work on these class objects. Object is an abstraction of real wold entity. Objects are the variables/instances of classes. MRI 6
- 7. Defining an Instance of a Class An object is an instance of a class Defined like structure variables: Rectangle r; Access members using dot operator: r.setWidth(5.2); cout << r.getWidth(); Compiler error if you attempt to access a private member using dot operator MRI 7
- 8. Classes and Objects A Class is like a blueprint and objects are like houses built from the blueprint MRI 8
- 9. Object-Oriented Programming Terminology attributes: members of a class methods or behaviors: member functions of a class MRI 9
- 10. More Object Terms data hiding: restricting access to certain members of an object public interface: members of an object that are available outside of the object. This allows the object to provide access to some data and functions without sharing its internal details and design, and provides some protection from data corruption MRI 10
- 11. Creating a Class Objects are created from a class Format: class ClassName { declaration; declaration; }; MRI 11
- 12. Classic Class Example MRI 12
- 13. Access Control in Classes Access specifiers in C++ class defines the access control rules. C++ has 3 new keywords introduced, namely, 1. public 2. private 3. protected These access specifiers are used to set boundaries for availability of members of class be it data members or member functions MRI 13
- 14. Access Specifiers Used to control access to members of the class public: can be accessed by functions outside of the class private: can only be called by or accessed by functions that are members of the class Protected, is the last access specifier, and it is similar to private, it makes class member inaccessible outside the class. But they can be accessed by any subclass of that class. (If class A is inherited by class B, then class B is subclass of class A. We will learn this later.) MRI 14
- 16. Access Specifiers MRI 16 Private Members Public Members
- 17. Types of Member Functions We already know what member functions are and what they do. Now lets study some special member functions present in the class. Following are different types of Member functions, 1. Simple functions 2. Static functions 3. Const functions 4. Inline functions 5. Friend functions MRI 17
- 18. Simple Member functions These are the basic member function, which don't have any special keyword like static etc as prefix. All the general member functions, which are of below given form, are termed as simple and basic member functions. return_type functionName(parameter_list) { function body; } MRI 18
- 19. Static Member functions Static is something that holds its position. Static is a keyword which can be used with data members as well as the member functions. A function is made static by using static keyword with function name. These functions work for the class as whole rather than for a particular object of a class. It can be called using the object and the direct member access . operator. But, its more typical to call a static member function by itself, using class name and scope resolution :: operator. MRI 19
- 20. Static Member functions Static is a keyword in C++ used to give special characteristics to an element. Static elements are allocated storage only once in a program lifetime in static storage area. And they have a scope till the program lifetime. Static Keyword can be used with following, Static variable in functions Static Class Objects Static member Variable in class Static Methods in class MRI 20
- 21. Static variables Static variables when used inside function are initialized only once, and then they hold there value even through function calls. These static variables are stored on static storage area , not in stack. void counter() { static int count=0; cout << count++; } int main() { for(int i=0;i<5;i++) { counter(); } } MRI 21
- 22. Const Member functions Const keyword makes variables constant, that means once defined, there values can't be changed. When used with member function, such member functions can never modify the object or it’s related data members. //Basic Syntax of const Member Function void fun() const {} MRI 22
- 23. Inline function C++ inline function is powerful concept that is commonly used with classes. If a function is inline, the compiler places a copy of the code of that function at each point where the function is called at compile time. To inline a function, place the keyword inline before the function name and define the function before any calls are made to the function. The compiler can ignore the inline qualifier in case defined function is more than a line.
- 24. Some Important points about Inline Functions 1. We must keep inline functions small, small inline functions have better efficiency. 2. Inline functions do increase efficiency, but we should not make all the functions inline. Because if we make large functions inline, it may lead to code bloat, and might affect the speed too. 3. Hence, it is adviced to define large functions outside the class definition using scope resolution ::operator, because if we define such functions inside class definition, then they become inline automatically. 4. Inline functions are kept in the Symbol Table by the compiler, and all the call for such functions is taken care at
- 25. Limitations of Inline Functions 1. Large Inline functions cause Cache misses and affect performance negatively. 2. Compilation overhead of copying the function body everywhere in the code on compilation, which is negligible for small programs, but it makes a difference in large code bases. 3. Also, if we require address of the function in program, compiler cannot perform inlining on such functions.
- 26. Friend function 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. Even though the prototypes for friend functions appear in the class definition, friends are not member functions. 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.
Editor's Notes
- #8: Show “Rectangle” class program.