classes.md

Classes in C++

• objects contain:
  • data in the form of member variables (also called instance variables).
  • as well as the functions we can use to interact with that data, in the form of member functions.
• objects allow us to provide information hiding.
  • We cannot see and interact with the private members of an object.
  • We can only use the public member functions.
• A class is a blueprint for objects (technically a bit more).
  • Name and type of the member variables.
  • Function prototypes for the member methods.
  • Implementations for the member methods.
  • Details on how to create objects (constructors).
  • BUT: each object has its own copies of the member variables.
• Two kinds of member functions:
  • modification member functions can change the object's values.
  • constant member functions cannot change the object's values.
• A class also provides a new type:
  • We can declare a variable of type the class.
  • We can pass objects of that arguments to functions.
• Declaring variables of a class: Always creates an object.
  • foo a; stores in a an object of class foo, by calling the default constructor.
  • foo a(5); stores in a an object of class foo, by calling an appropriate parametrized constructor.
  • foo a(b); where b is an object of class foo, uses the copy constructor to create a copy of the object in b and store it in a.
• Constructor syntax:
  • Same name as the class.
  • No return type.

Class syntax

// CLASS DECLARATION
// BIG COMMENT HERE
class throttle {
  public:
    // CONSTRUCTOR PROTOTYPES
    ...
    // MEMBER FUNCTION PROTOTYPES
    void shut_off();
    ...
  private:
    // MEMBER VARIABLES
    ...
};                 //  <---------- DONT FORGET THE SEMICOLON!!

// MEMBER FUNCTION IMPLEMENTATIONS COME LATER
void throttle::shut_off() {
  ...
}

Code organization

• Header files
  • extension .h
  • contains the parts other sections of the program need to know about
  • class definitions
  • class comment
  • macro guard to allow for multiple include without problems
  • never use using namespace ...
• Implementation files
  • extension .cpp
  • contains implementation of class methods
  • contains other helper methods and variables
  • include the header file