Primary template to compute 3 to the Nth and full specialization to end the recursion : Template specialization « template « C++ Tutorial

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/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>


// primary template to compute 3 to the Nth
template<int N>
class Pow3 {
  public:
    enum { result = 3 * Pow3<N-1>::result };
};

// full specialization to end the recursion
template<>
class Pow3<0> {
  public:
    enum { result = 1 };
};

int main()
{
    std::cout << "Pow3<7>::result = " << Pow3<7>::result
              << '\n';
}

Pow3<7>::result = 2187