how to use templates c++ code example

Example 1: function template

template <class T>
void swap(T & lhs, T & rhs)
{
 T tmp = lhs;
 lhs = rhs;
 rhs = tmp;
}

void main()
{
  int a = 6;
  int b = 42;
  swap<int>(a, b);
  printf("a=%d, b=%d\n", a, b);
  
  // Implicit template parameter deduction
  double f = 5.5;
  double g = 42.0;
  swap(f, g);
  printf("f=%f, g=%f\n", f, g);
}

/*
Output:
a=42, b=6
f=42.0, g=5.5
*/

Example 2: c++ template

#include <iostream>
using namespace std;

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

int main()
{
	int i1 = 1, i2 = 2;
	float f1 = 1.1, f2 = 2.2;
	char c1 = 'a', c2 = 'b';

	cout << "Before passing data to function template.\n";
	cout << "i1 = " << i1 << "\ni2 = " << i2;
	cout << "\nf1 = " << f1 << "\nf2 = " << f2;
	cout << "\nc1 = " << c1 << "\nc2 = " << c2;

	Swap(i1, i2);
	Swap(f1, f2);
	Swap(c1, c2);

        cout << "\n\nAfter passing data to function template.\n";
	cout << "i1 = " << i1 << "\ni2 = " << i2;
	cout << "\nf1 = " << f1 << "\nf2 = " << f2;
	cout << "\nc1 = " << c1 << "\nc2 = " << c2;

	return 0;
}

Example 3: templates of templates c++

namespace std {
  template<typename t> struct hash<MyClass<t>>
  {
  	size_t operator() (const MyClass<t>& c) const;
  }
}

// You can also do things like

template<template<typename t> class type> func_name<type<t>>();