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10. Default class members, conversion constructors, conversion operators

07/03/23

Default Member Functions​

  1. Default constructor (no parameters needed)
    • Constructor which takes no parameters.
    • The generated default constructor is empty
    • Why you can still create objects even when classes appear to have no constructors
    • Use ClassName() = default; to stop it
  2. Copy constructor (cone one object to another)
    • Used to initialise one object from another of the same type.
    • Returning object by value from a function
    • A copy constructor is created by default
    • Default behaviour copies each member in turn.
  3. An assignment operator (= operator)
    • Used when value of one object is assigned to another.
    • Create your own using operator overloading
    • Takes a reference to the one we are getting values from
  4. A destructor
    • Created if you do not create one
    • Gets called as members get destroyed
    • Basic data types just get destroyed
    • Pointers just get destroyed

General Rules​

  • If need a copy constructor, or an assignment operator, then probably need to create the other, plus a destructor as well

Conversion Constructors​

  • Conversion constructor is a constructor with one parameter
  • Converts from one type of object to another
  • Very similar to the copy constructor

Forcing explicit construction​

  • Providing a one-parameter constructor provides a conversion constructor
  • Allows compiler to use it to convert to the type whenever it wants/needs to do so
  • Use the keyword explicit

Conversion Operators​

  • Convert from a class into something else
  • Uses operator overloading syntax
  • Instead of an operator symbol, the new type name and () are used

Friends​

  • Members can be private, protected or public
  • Usually only class members can access private data
  • Class can grant access to their private member data and functions to their friends
  • The class still maintains control over which classes and functions have access
  • The friends of a class are treated as class members for access purposes - although they are not members
  • Declare your friends within your class body and use the keyword friend