template class 2 : template class « template « C++ Tutorial

1. C++ Tutorial
2. template
3. template class

/* 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>


template<typename T>
class AccumulationTraits;

template<>
class AccumulationTraits<char> {
  public:
    typedef int AccT;
    static AccT const zero = 0;
};

template<>
class AccumulationTraits<short> {
  public:
    typedef int AccT;
    static AccT const zero = 0;
};

template<>
class AccumulationTraits<int> {
  public:
    typedef long AccT;
    static AccT const zero = 0;
};


template <typename T>
inline
typename AccumulationTraits<T>::AccT accum (T const* beg,
                                            T const* end)
{
    // return type is traits of the element type
    typedef typename AccumulationTraits<T>::AccT AccT;

    AccT total = AccumulationTraits<T>::zero;
    while (beg != end) {
        total += *beg;
        ++beg;
    }
    return total;
}


int main()
{
    // create array of 5 integer values
    int num[] = { 1, 2, 3, 4, 5 };

    // print average value
    std::cout << "the average value of the integer values is "
              << accum(&num[0], &num[5]) / 5
              << '\n';

    // create array of character values
    char name[] = "templates";
    int length = sizeof(name)-1;

    // (try to) print average character value
    std::cout << "the average value of the characters in \""
              << name << "\" is "
              << accum(&name[0], &name[length]) / length
              << '\n';
}

the average value of the integer values is 3
the average value of the characters in "templates" is 108