CS240

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CS-240

• Classes (cont)
• Dick Steflik

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Member functions

• Member functions of a class include
• getters
• used to retrieve state data
• setters
• used to set state data
• mutators
• used to modify state data
• functions that model the classes behavior
• tend to be action words (verbs or verb phrases)
• take_off , reverse_direction, open ...

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Function prototypes

• Prototype are models of how a function is to be
  called
• are not necessarily part of the function
  definition, but may be
• float calculate_attack_angle (float, float)
• notice that in a prototype only the types are
  required, parameter names are not

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Function signatures

• The signature of a function consists of
• returned type (if any)
• the function name
• the ordered set of types in the parameter list
• within its scope, a functions signature must be
  unique even if its name is overloaded

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Parameters

• Parameters are required on a function definition
• parameter consists of a type and an identifier
• function formal parameters
• parameters in the function definition
• alias names for the actual arguments
• scope is local to the function
• parameters may be passed to a function
• by value
• by reference

ex. boolean exists(const point p)
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Value Parameters

• read only or input only parameters
• makes a local copy of the value for use in the
  function copies value of argument before running
  the function
• pass by value
• slower than pass by reference
• use only for small objects

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Reference Parameters

• read/write parameter value of argument can be
  changed
• uses address of argument to manipulate it
• doesnt require local storage
• use to identify reference parameters
• remember is the address operator

ex. void rotate (point p)
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Reference Parameters (cont.)

• use const reference parameters instead of value
  parameters (faster), less memory rqd.
• const indicates a promise to not modify the
  reference parameter exists

ex. double distance(const point p)
p is passed by reference as an input only
parameter
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Function Overloading

• The function name may be reused (overloaded)
  within a class
• each definition must have a unique signature
  (pattern made up of function name and the
  parameter types)

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Operator Overloading

• part of polymorphism
• for diadic (binary) functions i.e. functions
  with only two operands
• more convenient than naming special member
  functions to do the same thing
• general form left_op operator right_op

ex. boolean operator (const point lh, const
point rh) this overloads equality () for
objects of class point
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Friend Functions

• not a member function
• has access to private data
• member functions work with the current (named
  object) friend functions work with multiple
  objects of the same class
• tag as a friend of the class
• as part of class definition identify, by
  prototype, each friend of the class

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Friend Functions (cont.)

• Friend functions are needed in C due to Cs
  flawed object model, Java has a better model
  (all objects are derived from a single object).
• define the prototype in the public section of the
  class definition
• precede the prototype with the keyword friend

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Friend Functions (more)

• define the friend implementation in the .cpp file
  with the member functions
• do not precede the function name with the class
  name and the scoping operator (ex. classname)

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More Overloading Thoughts

• overload as a member function
• ! lt gt lt gt overload as a non-member (friend)
  returning a boolean
• gtgt ltlt (insertion and extraction) overload a
  non-members (friends) returning type iostream
• -/ (arithmetics) overload a non-members
• - ... overload same as and -

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Overloading
// in theClass definition... Time operator
(const Time ) // in the implementation... Tim
e Timeoperator(const Time oTime)
hour oTime.hour min oTime.min
am_pm oTime.am_pm miltime
oTime.miltime
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Time Class overloading
// in the class definition public
section... friend bool operator (const Time
, const Time ) // in the implementation
file..... bool TimeTime(const Time lhs ,
const Time rhs) return (lhs.miltime
rhs.miltime)
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Please note

• The only operators that cannot be overloaded are
• (scoping operator)
• . (dot operator)
• sizeof
• ? (three operands)