C %20Review%20(4)

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C Review (4)

• Pointers, Virtual Functions, and Template

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Templates
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Function Overloading

• C supports writing more than one function with
  the same name but different argument lists. This
  could include
• different data types
• different number of arguments
• The advantage is that the same apparent function
  can be called to perform similar but different
  tasks. The following will show an example of
  this.

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Function Overloadingdifferent data types

• void swap (int a, int b)
• int temp temp a a b b temp
• void swap (float c, float d)
• float temp temp c c d d temp
• void swap (char p, char q)
• char temp temp p p q q temp

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Function Overloading

• void swap (int a, int b)
• void swap (float c, float d)
• void swap (char p, char q)
• int main ( )
• int a 4, b 6
• float c 16.7, d -7.89
• char p 'M' , q 'n'
• swap (a, b)
• swap (c, d)
• swap (p, q)

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Templates

• Can we write code without being tied to
  particular type.
• Yes template
• But how?
• Question How do you swap two elements of any
  type?

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Templates

• Function Templates
• Class Templates
• Syntax for templates
• template ltclass Typegt
• Declaration
• Where type is the name of a data type, build-in,
  or user defined.
• Declaration is either function declaration or
  class declaration.
• Class refers to any user-defined or build-in type.

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Function templates

• Template ltclass Typegt
• void swap (Type a, Type b)
• Type temp
• temp a
• a b
• b temp

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Class templates

• template ltclass elemTypegt
• class listType
• Private
• elemType list100
• int length
• Public
• bool search(const elemType searchItem) const
• viod insert(const elemType newElement)

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Pointer
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Pointers

• A pointer is a variable that holds the address of
  something else.
• datatype identifier

foo
123
int foo int x foo 123 x foo
x
3
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Pointer variables

• Declaring pointers of simple data type
• int pInt
• char pCh
• double pNum
• Declaring pointers of structured data type
• Datatype pointerVariable
• Declaring pointers of pointer data type
• int p

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Pointer to Structs

• struct studentType
• string name
• int age
• double gpa
• studentType aStudent
• studentType pStudent

• pStudent aStudent
• /pStudent aStudent/
• aStudent.name Nan Wang
• (pStudent).age 18
• pStudent-gtgpa 4.0
• -gt member access operator arrow

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Pointer to Classes

• class studentType
• public
• string name
• int age
• double gpa
• void print() const
• studentType aStudent
• studentType pStudent

• pStudent aStudent
• /pStudent aStudent/
• aStudent.name Nan Wang
• (pStudent).age 18
• pStudent-gtgpa 4.0
• pStudent-gtprint()
• -gt member access operator arrow

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Passing pointers as parameters

• void swap( int x, int y)
• int tmp
• tmp x
• x y
• y tmp

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• Dynamic Objects

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Memory Management

• Static Memory Allocation
• Memory is allocated at compilation time
• Dynamic Memory
• Memory is allocated at running time

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Static vs. Dynamic Objects

• Dynamic object
• Memory is acquired by program with an allocation
  request
• new operation
• Dynamic objects can exist beyond the function in
  which they were allocated
• Object memory is returned by a deallocation
  request
• delete operation

• Static object
• (variables as declared in function calls)
• Memory is acquired automatically
• Memory is returned automatically when object goes
  out of scope

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Memory Allocation
new delete
int a200
int ptr ptr new int200 delete ptr
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Object (variable) creation New

• Syntax
• ptr new SomeType
• where ptr is a pointer of type SomeType

Example
int p new int
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Object (variable) destruction Delete

• Syntax
• delete p
• storage pointed to by p is returned to free
  store and p is now undefined

Example
int p new int p 10 delete p
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p
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Array of New dynamic arrays

• Syntax
• P new SomeTypeExpression
• Where
• P is a pointer of type SomeType
• Expression is the number of objects to be
  constructed -- we are making an array
• Because of the flexible pointer syntax, P can be
  considered to be an array

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Example

• Dynamic Memory Allocation
• Request for unnamed memory from the Operating
  System
• int p, n10p new int
• p new int100

p
new
p
new
p new intn
p
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Memory Allocation Example

• Want an array of unknown size

int main() cout ltlt How many students?
cin gtgt n int grades new
intn for(int i0 i lt n i)
int mark cout ltlt Input Grade for
Student ltlt (i1) ltlt ? cin gtgt
mark gradesi mark . .
. printMean( grades, n ) // call a function
with dynamic array . . .
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Freeing (or deleting) Memory
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Virtual function
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Virtual Functions

• A virtual function is a function whose behavior
  can be overridden within an inheriting class by a
  function with the same signature.
• virtual void eat() const stdcout ltlt "I eat
  like a generic Animal." ltlt stdendl

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output
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Purpose of Virtual function

• In OOP when a derived class inherits from a base
  class, an object of the derived class may be
  referred to (or cast) as either being the base
  class type or the derived class type. If there
  are base class functions overridden by the
  derived class, a problem then arises when a
  derived object has been cast as the base class
  type. When a derived object is referred to as
  being of the base's type, the desired function
  call behavior is ambiguous.

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• The distinction between virtual and not virtual
  resolves this ambiguity. If the function in
  question is designated "virtual" in the base
  class then the derived class's function would be
  called (if it exists). If it is not virtual, the
  base class's function would be called.
• Virtual functions overcome the problems with the
  type-field solution by allowing the programmer to
  declare functions in a base class that can be
  redefined in each derived class.

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Abstract Class
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Abstract classes

• Sometimes, we want to have a class to represent
  something, but we dont want anyone to actually
  create an instance of that class.
• We do this because we except people to inherit
  from our base class, and then create instances of
  the derived class.
• An abstract class is a class that is designed to
  be specifically used as a base class.

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Abstract Class

• An abstract class contains at least one pure
  virtual function. You declare a pure virtual
  function by using a pure specifier ( 0) in the
  declaration of a virtual member function in the
  class declaration.

class AB public virtual void f() 0
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Abstract Classes

• An abstract class represents an abstract concept
  in C (such as Shape class)

1. Defines the interfaces that all of the concrete
   classes (subclasses) share
2. Does not define state and implementation unless
   it is common to all concrete classes
3. Cannot be instantiated

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Linear List As C Abstract Class

• templateltclass Tgt
• class linearList
• public
• virtual linearList()
• virtual bool empty() const 0
• virtual int size() const 0
• virtual T get(int theIndex) const 0
• virtual int indexOf(const T
  theElement)const 0
• virtual void erase(int theIndex) 0
• virtual void insert(int theIndex,
• const T theElement)
  0
• virtual void output(ostream out) const
  0

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Extending A C Class

• templateltclass Tgt
• class arrayList public linearListltTgt
• // code for all abstract methods of linearList
  must come here
• class linkedList public linearListltTgt
• // code for all abstract methods of linearList
  must come here