Class Templates

Class Templates

•  Using class template we can write a class whose members use template parameters as types.

•  The syntax of class template declaration is

template<class Type >

class classname

 {

…          //body of class

…

};

•  In above example Type can be of any data type. Then template class member function is defined. The complete program using class template is as given below.

#include <iostream>

using namespace std;

template<class T >

class compare {  //writing the class as usual

Ta, b;//note we have used data type as T

public:

Compare (T first, T second)

{

      a=first;

      b=second;

}

T max ();//finds the maximum element among two

};

//template class member function definition

//here the member function of template class is max

template<class T>

T Compare <T> ::max ()

{

      T val;

      if(a>b)

            val=a;

      else

            val=b;

      return val;

}

int main()

{

Compare <int> obj1 (100, 60);//comparing two integers

Compare <char> obj2('p','t');://comparing two characters

 cout<<"\n maximum(100,60) = "<obj1.max();

cout<<"\n maximum('p','t') = "<obj2.max();

retrun 0;

}

Output

maximum(100,60) = 100

maximum('p','t') = t

• In above program, Compare is a class in which two variable a and b are declared for comparison. The function max is used to find the maximum number among the two. The T is used to indicate the data type. If we create an object of type integer by

         Compare <int> obj1(100,60)

then two integer values will be compared. Similarly one can compare two characters, two real values by declaring appropriate objects.

 

Difference between function template and class template

• Function templates are those functions which can handle different data types without separate code for each of them. For a similar operation on several kinds of data types, a programmer need not write different functions.

Using class template we can write a class whose members use template parameters as types.

 

Example:1

Implement circular queue with proper insertion and deletion operations using class templates.

Solution :

#include<iostream>

using namespace std;

#define size 10

/*‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

Class Definition using class template

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒*/

template<class T>

class Queue

{

T Que[size];

int front, rear;

public:

Queue()//constructor defined

{

      front = ‒1;

      rear = 0;

}

void init();

void insert(T ch);

T delet();

void display();

};

template <class T>

void Queue<T>::init()

{

      for (int i = 0; i< size; i++)

            Que[i] = 0;

}

/*‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

insert function

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒*/

template<class T>

void Queue<T>::insert(T item)

{

if (front = = (rear + 1) % size)

{

      cout<<"Queue is full\n";

}

else

{

      //setting front pointer for a single element in Queue

      if(front = = ‒1)  

            front =  rear= 0;

      else

            rear = (rear + 1)% size;

      Que[rear] = item;

}

}

/*‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

delet function

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒*/

template<class T>

T Queue<T>::delet()

{

T val;

if (front = = ‒1)

{

      cout << "Queue is empty\n";

      return 0; // return null on empty Queue

}

val = Que[front]://item to be deleted

if (front = = rear)//when single element is present

{

      front = rear = ‒1;

}

else

      front = (front + 1) % size;

return val;

}

/*‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

Display function

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒*/

template <class T>

void Queue<T>::display()

{

int i;

while (i!= rear)

med to indvan

{

      cout << Que[i] << " ";

      i = (i + 1) % size;

}

cout << Que[i] << endl;

}