Templates

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Non-Type Template Parameter

A non-type parameter is like a regular parameter with a type and a variable. This can be assigned a value when invoking the template function.

File:: template3.cpp

#include <iostream>
#include <string.h>

using namespace std;


template <class T, class Y> void console (T a1, Y b1)
{
  cout << a1 << " " << b1 << endl ;
}

template <class T, class Y, int i1> void console (T a1, Y b1)
{
  cout << a1 << " " << b1 << " " << i1 << endl ;
}


int main ()
{
	int i1=5  ;
	string str1 = "demo" ;
	console( 5, str1 ) ;
	console<int, string, 10>( 5, str1 ) ;
	return 0;
}

ajay.mittal@USEUG-57MJ2J3 ~/cplus
$ g++ template3.cpp  ; ./a.exe
5 demo
5 demo 10

The above program shows that we can pass more than 1 class parameter into the function. We can also choose to define the type in the template parameters and then give a constant value for it that we can access later on. The "console( 5, str1 ) ;" calls the template function and the types in the template function are deduced to be "int" and "string" .
We can overload the template functions with normal functions.

File:: template4.cpp

#include <iostream>

using namespace std;


template <class T> T GetMax (T a1, T b1)
{
	T result;
	result = (a1>b1)? a1 : b1 ;
	cout << "Inside the template function." << endl ;
	return (result);
}

int GetMax (int a1, int b1)
{
	int result;
	result = (a1>b1)? a1 : b1 ;
	cout << "Inside the normal function." << endl ;
	return (result);
}


int main ()
{
	int i1=5, j1=6, k1;
	long l1=10, m1=5, n1;

	k1 = GetMax(i1, j1 );
	n1 = GetMax(l1, m1 );
	cout << k1 << endl;
	cout << n1 << endl;
	return 0;
}

The normal function will get called if the arguments match and if not then the template function will be called.

File:: template5.cpp

#include <iostream>

using namespace std;


template <class T , class Y=int> T GetMax (T a1, Y b1)
{
	T result;
	result = (a1>b1)? a1 : b1 ;
	return (result);
}



int main ()
{
	int i1=5, j1=6, k1;
	long l1=10, m1=5, n1;

	k1 = GetMax<int>(i1, j1 );
	n1 = GetMax<long,long>(l1, m1 );
	cout << k1 << endl;
	cout << n1 << endl;
	return 0;
}

Normal functions can have default argument values and similarly template functions parameters can have default values as the above example shows.