Function Templates

Function Templates

• To perform identical operations for each type of data compactly and conveniently, the function templates are used. One can write a single function template definition. Based on the argument types provided in calls to the function, the compiler automatically instantiates separate object code functions to handle each type of call appropriately. Thus the same functional code with different data type elements can be handled. For instance using add function one can perform addition of two integer values or two double values or two float values.

• The syntax of function template is as follows ‒

template <class name_of_data_type>

name_of_data_type function_name (name_of_data_type id1,... name_of_data_type id2)

For example :

template<class T>

T min(T a, T b)

•  Here template is a keyword used to represent the template. Then inside the angular bracket keyword class is followed by the data type name T. The compiler will replace T by the appropriate data types.

• Function templates are implemented like regular functions, except they are prefixed with the keyword template. Here is a sample with a function template.

C++ Program

#include <iostream>

using namespace std;

//min returns the minimum of the two elements

template<class T>

T min(T a, T b)

{

      if (a<b)

            return a;

      else

            return b;

}

int main()

{

      cout << "min(10, 20)  = " << min(10, 20) << endl;

      cout << "min('p', 't')  =" << min('p', 't') << endl;

      cout << "min(10.3, 67.2) = " <<min(10.3,67.2)<<endl;

      return 0;

}

Output

min(10, 20) = 10

min('p', 't') = p

min(10.3, 67.2) = 10.3

• Use of function templates is very easy: We can use them like regular functions. When the compiler sees an instantiation of the function template, for example: the call min(10, 20) in function main, the compiler generates a function min(int, int). Similarly the compiler generates definitions for min(char, char) and min(float, float) on encountering the corresponding values.

 

Example :1

 What is function template? Write a template function to sort arrays of float and int using bubble sort.

Solution:

Function template: Function template defines the general set of operations that will be applied on various types of data. This data can be passed to this function as a argument.

/**************************************************************************

Program to sort the arrays of float and int using bubble sort with the help of function template

***************************************************************************/

#include<iostream>

#define size 10

using namespace std;

template<class T>

void bubble(T A[size],int n)

{

T temp;

for(int i=0;i<=n‒2;i++)

{

       for(int j=0;j<=n‒2‒i;j++)

       {

              if(A[j]>A[j+1])

              {

                     temp=A[j];

                     A[j]=A[j+1];

                     A[j+1]=temp;

              }

       }

}

cout<<"\n The sorted List is ...\n";

for(i=0;i<n;i++)

       out cout<<" "<<A[i];

}

void main()

{

int A1[size];

float A2[size];

cout<<"\n\t\t Bubble Sort\n";

int i,n;

cout<<"\n\t‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒";

cout<<"\n\t Handling Integer Elements";

cout<<"\n\t‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒";

cout<<"\n How many elements are there?";

cin>>n;

cout<<"\n Enter the Integer elements\n";

for(i=0;i<n;i++)

cin>>A1[i];

bubble(A1,n);

cout<<"\n";

cout<<"\n\t‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒";

cout<<"\n\t Handling Float Elements";

cout<<"\n\t‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒";

cout<<"\n How many elements are there?";

cin>>n;

cout<<"\n Enter the float elements\n";

for(i=0;i<n;i++)

cin>> A2[i];

bubble(A2,n);

Output

Bubble Sort

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

Handling Integer Elements

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

How many elements are there?5

Enter the Integer elements

33 22 55 44 11

The sorted List is ...

11 22 33 44 55

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

Handling Float Elements

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

How many elements are there?5

Enter the float elements

44.4 22.2 11.1 55.5 33.3

The sorted List is

11.1 22.2 33.3 44.4 55.5

 

Example : 2

Write C++ program to sort the list of integers, floating point numbers and characters by Quick sort mechanism using function template.

Solution :

#include<iostream>

using namespace std;

#define SIZE 5

template <class T>

void quicksort(T [], int, int);

/*

This function is to sort the elements in a sublist

*/

template<class T>

void quicksort(T arr[], int p, int q)

{

      int j;

      if (p<q)

      {

            j = partition(arr,p, q + 1);//setting pivot element

            quicksort(arr,p, j‒1);//splitting of list

            quicksort(arr,j + 1, q);//splitting of list

      }

}

*/

This function is to partition a list and decide the pivot element

*/

template<class T>

T partition(T arr[],int m, int p)

{

T pivot = arr[m];

int i=m, j = p;

do

{

do

{

      i++;

} while (arr[i]<pivot);

do

{

      j‒‒;

} while (arr[j]>pivot);

if (i<j)

      swap(i, j);

} while (i<j);

arr[m] = arr[j];

arr[j] = pivot;

return j;

}

template<class T>

void swap(int i, int i)

{

      T p;

      p = arr[i];

      arr[i] = arr[j];

      arr[j] = p;

}

void main()

{

cout << "\n\t\t Quick Sort Method \n";

int arr[] = { 5,2,3,1,4 };

quicksort(arr,0, SIZE‒1);

cout << "\n The sorted list of integers is\n";

for (int i = 0; i < SIZE; i++)

      cout <<<< arr[i];

char arr1[] = { 'E','B','C', 'A','D'};

quicksort(arr1, 0, SIZE ‒ 1);

cout << "\n The sorted list of characters is\n";

for (int i = 0; i < SIZE; i++)

      cout << " " << arr1[i];

float arr2[] = {5.5,2.2,3.3,1.1,4.4 };

quicksort(arr2, 0, SIZE ‒ 1);

cout << "\n The sorted list of floats is\n";

for (int i = 0; i < SIZE; i++)

      cout << " " << arr2[i];

}

Output

      Quick Sort Method

The sorted list of integers is

12345

The sorted list of characters is

A B C D E

The sorted list of floats is

1.1 2.2 3.3 4.4 5.5

 

Review Question

1. Explain function templates with an example.