Chapter 15 C++ Function By C. Shing ITEC Dept Radford University.

Chapter 15 C++ Function

By C. Shing

ITEC Dept

Radford University

Slide 2

Objectives Understand how to create and free dynamic

memory Understand the scope rule Understand pass by reference Understand member functions Know how to write inline functions Understand function overloading Understand static function Understand template function and virtual function

Slide 3

Dynamic Memory Create a memory pointed by memPtr (calls constructor)Form: type * memPtr=new type;Example: int * numberPtr=new int;

Destroy the dynamic memory memPtr(calls destructor)Form: delete memPtr;Example: delete memPtr;

Slide 4

Dynamic Memory (Cont.) Create an array of memory

pointed by arrayPtrForm: type * arrayPtr=new type[SIZE];Example: int * numberarrayPtr=new int[SIZE];

Destroy the dynamic array memory arrayPtrForm: delete [] arrayPtr;Example: delete [] numberarrayPtr;

Slide 5

Scope Rule The variable is meaningful and unique

in its defined block The local variable redefined scope precedes

the global variable if use the same name.

The global variable can be referred using

::local variable name

Slide 6

Scope Rule (Cont.)Example:int number = 10;Int main(){

int number = 100; cout << “ local number= “<<number; cout << “ global number= “<<::number;}

Slide 7

Pass By Reference The function directly access the variables

passed

in using reference.

(This is different from passing pointers)

Slide 8

Pass By Reference (Cont.)Example:Int main(){

int number=10; byRef(number);

cout << number; // print 100}void byRef(int &number){

number=100;}

Slide 9

Pass By Reference - Example Array of Pointers: Store array of stringsAssume that array w has 5 cells, each stores an address of strings as follows:w[0]=100=address of string “this”w[1]=200=address of string “is”w[2]=300=address of string “a”w[3]=400=address of string “snow”w[4]=500=address of string “day”

Slide 10

Pass By Reference – Example (Cont.)

Bubble sort for array w: To call sort_strings – sort_strings(w, size) To use bubble sort to sort the array w:void sort_strings (char * w[], int n){ int i, j; for (i=0; i<n; ++i) for (j=i+1; j<n;++j)

if (strcmp(w[i],w[j])>0) swap (w[i], w[j]);

}

Slide 11

Pass By Reference – Example (Cont.) Example: (Cont.) You may also write it asvoid swap (char * &s, char * &t){ char *tmp; tmp=s; s=t; t=tmp;}

Slide 12

Pass By Reference – Example (Cont.)

Without using class:

bubble.cpp

bubble_data.txt

Using class:

bubbleclass.cpp

bubble_data.txt

Slide 13

Pass By Pointer – Example (Cont.)Bubble sort for array w: To use bubble sort to sort the array w:void sort_strings (char *w[], int n){ int i, j; for (i=0; i<n; ++i) for (j=i+1; j<n;++j)

if (strcmp(w[i],w[j])>0) swap (&w[i], &w[j]);

}

Slide 14

Pass By Pointer – Example (Cont.) Example: (Cont.) The swap function isvoid swap (char *s[], char *t[]){ char *tmp; tmp=*s; *s=*t; *t=tmp;}

Slide 15

Pass By Pointer – Example (Cont.) Using class:

bubbleclassPtr.cpp

bubble_data.txt

Slide 16

Functions member functions:

only functions that can access member in the class Default constructor: missing parameters will be

initialized automatically by the default values inline function:

short function that can fit in one line constant function: function that does not change any

member data, not allowed for constructor or destructor.

A non-constant function is not allowed to access

constant object.

Slide 17

Functions (Cont.) friend function:

not a member function but can access member

data static function (no this pointer available)

function that returns

static variable (share among all objects created)

without any object exists

Slide 18

Functions (Cont.) Overloading

Function overloading: function with different

argument list, each function performs different

task Operator overloading: rewrite rule for existing

operator on object (not change operator precedence

nor the operator characteristics)

Slide 19

Functions (Cont.) Template

Template function: same task for different

data types Class template: specify template for entire class member data

and member functions

Slide 20

Functions (Cont.) Virtual function: used to specify interface

function and will be implemented in various

inherited classes (discussed in Polymorphism)

Slide 21

Member Function – Default Constructor Form:

Class Name (type = default value, …)

Example:

default constructor for 2D Point class

Point (int=0, int=0);

Slide 22

Member function - inlineExample:Class 3DPoint{

public: 3DPoint(double =0.0, double =0.0,

double =0.0); double getX() { return x;} // this is inline function

…private:

double x, y, z;}

Slide 23

Member function - constantExample:Class 3DPoint{

public: 3DPoint(double =0.0, double =0.0,

double =0.0); double getX() const { return x;} // constant function

…private:

double x, y, z;}

Slide 24

Member function – inline and constant function Example

Using class: a 3D Point class

point.cpp

Use this pointer for cascading member

function call

pointThis.cpp

Slide 25

Member function - friendExample:Class Point{

friend Point &setPoint(double, double, double);public:

Point(double =0.0, double =0.0, double =0.0);

double getX() const { return x;} // constant function…

private:double x, y, z;

}

Slide 26

Member function – friend (Cont.)Example: (Cont.)Point &setPoint(Point &p,

double sx, double sy, double sz){

p.x = sx;p.y = sy;p.z = sz;

return p;}

Slide 27

Member function – friend function Example

Using class: a 3D Point class

pointFriend.cpp

Slide 28

Member function - staticExample:Class Point{

friend Point &setPoint(double, double, double);public:

Point(double =0.0, double =0.0, double =0.0);

…// static function to access static member datastatic int howmany ();

private:double x, y, z;static int pointCount;

}

Slide 29

Member function – static (Cont.)Example: (Cont.) // initialize static member dataint Point::pointCount=0;

// constructorPoint::Point(double sx, double sy, double sz)// member initializer: assign sx to x, sy to y and sz to z:x(sx), y(sy), z(sz)

…pointCount++;

}

Slide 30

Member function – static (Cont.)Example: (Cont.) // static function definitionint Point::howmany(){

return pointCount;}

// main functionint main(){

…cout<< "Total number of points created = "<<Point::howmany()<<endl;

}

Slide 31

Member function – static function Example

Using class: a 3D Point class

pointStatic.cpp

Slide 32

Operator OverloadingExample:

Class Point{

friend istream &operator>> (istream &, Point &);public:

Point(double =0.0, double =0.0, double =0.0);

…private:

double x, y, z;}

Slide 33

Operator Overloading (Cont.)Example: (Cont.) // input form: (m,n,r) istream &operator>> (istream &input, Point &p){

input.ignore();input >> p.x;input.ignore();input >> p.y;input.ignore();input >> p.z;input.ignore(5,'\n');return input;

}

Slide 34

Operator Overloading (Cont.)Example: (Cont.)int main(){

Point p, q;p.output();cout<<"Please enter in 2 points in the form: (m,n,r),” << “ e.g. (1.2,3.45,67.891)";cin >> p >> q;p.output();q.output();cout << '\n';

}

Slide 35

Operator Overloading (Cont.) Example

Using class: a 3D Point class

overload.cpp

Slide 36

Template Function Form:

template <class T1, class T2>

returntype functionname (T1 var1 , T2 var2)

{

…

}

Slide 37

Template Function (Cont.) Example: template function for swap

template <class T>void Bubble::swap(T &x , T &y){

T tmp;

tmp = x;x = y;y = tmp;

}

Slide 38

Template Function (Cont.)

bubbleclass_template.cpp

bubble_data.txt

Slide 39

Class template Form:template <class T>class classname {public:

classname();returntype memberfunction (T var1, …);T memberfunction (T var1, …);~ classname();

private:T var3; int var4, …;;

};

Slide 40

Class template (Cont.) Form: (Cont.)

template <class T>

classname<T>::classname ()

{

…

}

Slide 41

Class template (Cont.) Example: A Bubble sort classtemplate <class T>class Bubble {public:

Bubble();void PrintData();void sort();~Bubble();

private:T student[MAX_CLASS_SIZE]; int numStudents;void swap(T &x , T &y);

};

Slide 42

Class template (Cont.) Example: A Bubble sort class (Cont.)template <class T>Bubble<T>::Bubble(){

numStudents=0;

while (cin>>student[numStudents]) {numStudents++;

}}

Slide 43

Class template (Cont.) Complete Example:

No template:

bubbleclass_string.cpp

bubble_data.txt

Slide 44

Class template (Cont.) Complete Example: (Cont.)

Use class template :

bubble_classtemplate1.cpp

bubbleclasstemplate1_data.txt (string data)

bubble_classtemplate2.cpp

bubbleclasstemplate2_data.txt (int data)

Slide 45

References Deitel & Deitel: C How to Program, 4th ed.,

Chapter 15, 16 & 17, Prentice Hall