cs60 Discussion week9


Lastweek
Bitoperators
Buffered IO
Overloading operators

Overview


Standard class
virtual methods
templates

Standard Class


Builtin simple types 

  int, char, double, ...

Builtin constructed types 

  struct/union

What operations are available to *all* builtin types


1.  Can I compare 2 structs?
2.  Can I assign

--> creation/assignment/destruction


What operations are available to *all* numeric types

+ - / * % comparison

What operations are available to *all* integer types

& ^ | ~


C++ allows programmer to add types that seem built-in

How?  compare int to class Num { int *values; };
0
main() {
  int a;   //create an unitialized int
  Num n;   // create ... Num

  int a[10];
  Num n[10];
}

class Num
{
public:
   Num();
};

1.   The 'default constructor' allows simple declarations and 
	*arrays* to be defined....


What about initialized ints
---------------------------

main() {
  int a (1), b = 1;   //create an itialized int
  Num n(1), m = 1;   // create ... Num
  Num x = n;
}


class Num
{
public:
   Num();
   Num (const Num&x);
};

1.  The 'copy-constructor' allows objects to be initialized from
    other object of the same type.

Assignment  and comparison
---------------------------

main() {
   int a;
   Num x, y;
   a = 2;
   x = y;

   if (a < b) {...}
   if (x < y) {   }
}

// Big number class 
class Num 
{
public:
   Num();
   Num(const Num&);
   ~Num();

   Num& operator = (const Num&);
   bool operator == (const Num&);
   bool operator < (const Num&);
};

1.  The 'assignment operator' allow the assignment of the 
    type.
2.  Why does it take 'const Num&' and why does it return Num&


viritual functions
------------------


Java/C++ support polymorphism


class Graphic {
virtual void draw ();
};

class Rect : public Graphic
  virtual void draw (); 
}

class Circle : public Graphic
  virtual void draw (); 
}


A polymorphic call is made to the object based on
it's type.

Graphic *items[10]

items[0] = new Circle();
items[1] = new Rect();

for (int i=0; i<10; i++)
  items[i]->draw();    // Calls whats?


1.  You must declare the each function virtual
2.  The base class must be declared virtual


How about deletion of the the object?

for (int i=0; i<10; i++)
  delete items[i];   // Calls which one???


1.  You need to add a virtual destructor

    class Graphic {

      virtual ~Graphic();
    };

2.  Can constructors be virtual?



Abstract class
--------------

A class that is a base class for other (polymorphic)
but may not be constructed

   class Graphic {

     virtual draw () = 0;
   }


   Graphic *g = new Graphic(); // ERROR

   Graphic *g = new Rect ();  // OK has a draw method defined.