Intro to Object Oriented Programming

Where as defining new C data types used struct, we use classes to define new data types in C++.

Overview of classes

Features of classes:

• Include functions that directly operate on the fields.
  • Special functions called constructors are used to initialize class objects (also called instances - variables declared to be of a class type).
  • Special functions called destructors are used to perform clean-up operations just before the lifetime of a class instance ends.
• Add protection levels for the fields and functions (e.g. private) to provide data hiding and encapsulation.
• Use inheritance to define a class by extending an existing class.

stream class Hierarchy

Inheritance: class A inherits from class B if every class A object is-a class B object also.

• istream and ostream are both derived from ios.
• iostream inherits from both istream and ostream.
  • Note that multiple inheritance is allowed. A class can derive from multiple classes
• steam extraction (>>) operator defined for all istreams and insertion (<<) operator defined for all ostreams, and because fstream and stringstream are both derived from iostream, they can use both << and >>.

file input (std::ifstream)

• ifstream has a constructor taking a string specifying the filename.
  • Calling the constructor with a filename is the same as calling fopen with the filename using a r flag.
  • The file must already exist.
• since ifstream inherits from istream, we get the insertion (<<) operator.
• ifstream has a destructor that closes the file. When the ifstream object's lifetime ends, it automatically closes itself.