Chapter 2 Objects and Classes Bernard Chen Spring 2006

2.1 What is OO programming? Object: an atomic unit that has structure and state Information hiding: Black-box analogy Encapsulation: grouping of data and functions Inheritance: mechanism allows extending functionality of an object.

How does C++ support OO Template: the logic is independent of the type Inheritance Polymorphism: allows us to implement new types (classes) that share same logic

2.2 Basic Class Syntax Class members: either data or functions and categorized into either public, protected,or private. Public: visible to an instance of (object) a class Private: visible only inside an instance of a class Protected: similar to private but visible to derived classes. Default: all members are private

Constructors Member functions that describe how an object is declared and initialized. If no constructor defined, compilers will generate one called default constructor. Explicit constructors prevent automatic type conversion.

Constant Member Function Constant functions (accessors) : functions that do not change any data member. const is a part of the function signature. [const] return_type name([const] parameter_list) [const]; Interface: describes what can be done to the object, i.e. the header. Implementation: represents internal processes specified by the interface.

Big three: Destructor, Copy Constructor, and Operator = •Destructor tells how an object is destroyed and freesdresources when it exists scope. ~IntCell(); •Copy Constructor allows a new object construct using the data in an existing one. IntCella(5); // a new IntCellcall a IntCellb(a); // another IntCellcall b •Operator = copy assignment, copies data members using = by default.=> may cause shallow copying.

This (predefine pointer)

2.3 Additional C++ Features Operator overloading: extending the types to which an operator can be applied. example: string x=“Mary’s score is:”; int y=95; string z=x+y; “.”, “.*”, “?:”, “sizeof” can’t be overloaded

Additional C++ Features Type conversion creates a temporary object of a new type– Example: int a = 5; double b = a; //implicit cast

2.5 Exceptions (report error) An object that stores information transmitted outside the normal return sequence and is used to signal exceptional occurrences Handle exceptions by throw and catch clauses.

Exceptions example try { for (intn=0; n<=10; n++) if (n>9) throw "Out of range"; } } catch (char * str) cout<< "Exception: " << str<< endl;

2.6 String Class C string: array of character terminated by ‘\0’ C++ standard string: a STL class with all overload operators and built-in functions http://www.bgsu.edu/departments/compsci/docs/string.html

Summary Construction/ destruction of objects Copy semantics Overloading Implicit/explicit type conversion Information hiding/atomicity