Template C++

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• Templates are the basis for generic programming in C++. which involves writing code in a way that is independent of any particular type.

• It allows you to write generic programs. In simple words, you can create a single function or a class to work with different data types using templates.

• The concept of templates can be used in two different ways:
  1. Function Templates
  2. Class Templates
  
  

• The keyword template is use to create Generic class or Generic function.

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Function Template:

A single function template can work with different data types at once but, a single normal function can only work with one set of data types.

The general form of a template function is:

Syntax:

template < class type >
return-type function-name(arg-list)
    {
     T var;
     //YOUR CODE
    }         

In the above code, T is a template argument that accepts different data types (int, float), and class is a keyword.

You can also use keyword typename instead of class.

Example:

A function template that returns the maximum of two values:

#include<iostream>
#include<string>
using namespace std;

template <class T>
T getMax (T const& a, T const& b)  
{ 
   return a > b ? a:b; 
} 

int main () {
 
 int i = 20;
 int j = 50;
 cout << "getMax(i, j): ";
 cout<< getMax(i, j) << endl; 

 double f1 = 10.5; 
 double f2 = 30.5; 
 cout << "getMax(f1, f2): ";
 cout<< getMax(f1, f2) << endl; 

 string s1 = "Hello"; 
 string s2 = "World"; 
 cout << "getMax(s1, s2): ";
 cout << getMax(s1, s2) << endl; 

 return 0;
}                 

OUTPUT:

Max(i, j): 50
Max(f1, f2): 30.5
Max(s1, s2): World

Example:

Program to swap data using function templates:

#include<iostream>
using namespace std;

template <class T>
void Swap(T &n1, T &n2)
{
 T temp;
 temp = n1;
 n1 = n2;
 n2 = temp;
}

int main()
{
 int a = 10, b = 20;
 float f1 = 3.5, f2 = 2.5;
 char c1 = 'a', c2 = 'b';

 cout << "Before Swapping:\n";
 cout << " a = " << a << "     b = " << b;
 cout << "\nf1 = " << f1 << "  f2 = " << f2;
 cout << "\nc1 = " << c1 << "    c2 = " << c2;
 
 Swap(a, b);
 Swap(f1, f2);
 Swap(c1, c2);

 cout << "\n\nAfter Swapping:\n";
 cout << " a = " << a << "     b = " << b;
 cout << "\nf1 = " << f1 << "  f2 = " << f2;
 cout << "\nc1 = " << c1 << "    c2 = " << c2;

 return 0;
}                        
                    

OUTPUT:

Before Swapping:
 a = 10    b = 20
f1 = 3.5  f2 = 2.5
c1 = a    c2 = b 
After Swapping:
 a = 20    b = 10
f1 = 2.5  f2 = 3.5
c1 = b    c2 = a

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Class Template:

Like function templates, you can also create class templates for generic class operations.

Syntax:

template<class T>
class className
{
   ... .. ...
public:
   T var;
   T function(T arg);
   ... .. ...
};         

Here, type is the placeholder type name, which will be specified when a class is instantiated. You can define more than one generic data type by using a comma-separated list.

Object Creation of template class:

className<dataType> classObject;                        
                    

Code Example:

#include<iostream>
using namespace std;
template<class T>
class Calculator{
public :
void sum(T n1, T n2){
T res = n1 + n2;
cout<<"ADD RESULT : ";
cout<< res<< endl;
}
void mul(T n1, T n2){
T res = n1 * n2;
cout<<"MULTIPLY RESULT : ";
cout<< res<< endl;
}
void square(T n1){
T res = n1 * n1;
cout<<"SQUARE RESULT : ";
cout<< res<< endl;
}
};
int main() {
Calculator<int> ob1;
ob1.sum(20,10);
ob1.mul(20,10);
ob1.square(8);
Calculator<float> ob2;
ob2.sum(20.2f,10.7f);
ob2.mul(1.5f,10.0f);
ob2.square(4.0f);
return 0;
}              

OUTPUT:

ADD RESULT : 30
MULTIPLY RESULT : 200
SQUARE RESULT : 64
ADD RESULT : 30.9
MULTIPLY RESULT : 15.0
SQUARE RESULT : 16.0

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