template class for insert iterator for associative containers : custom iterater « STL Algorithms Iterator « C++ Tutorial

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2. STL Algorithms Iterator
3. custom iterater

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * 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>
#include <set>
#include <algorithm>
using namespace std;


/* PRINT_ELEMENTS()
 * - prints optional C-string optcstr followed by
 * - all elements of the collection coll
 * - separated by spaces
 */
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
    typename T::const_iterator pos;

    std::cout << optcstr;
    for (pos=coll.begin(); pos!=coll.end(); ++pos) {
        std::cout << *pos << ' ';
    }
    std::cout << std::endl;
}


#include <iterator>

/* template class for insert iterator for associative containers
 */
template <class Container>
class asso_insert_iterator
 : public std::iterator <std::output_iterator_tag,
                         void, void, void, void>
{
  protected:
    Container& container;    // container in which elements are inserted

  public:
    // constructor
    explicit asso_insert_iterator (Container& c) : container(c) {
    }

    // assignment operator
    // - inserts a value into the container
    asso_insert_iterator<Container>&
    operator= (const typename Container::value_type& value) {
        container.insert(value);
        return *this;
    }

    // dereferencing is a no-op that returns the iterator itself
    asso_insert_iterator<Container>& operator* () {
        return *this;
    }

    // increment operation is a no-op that returns the iterator itself
    asso_insert_iterator<Container>& operator++ () {
        return *this;
    }
    asso_insert_iterator<Container>& operator++ (int) {
        return *this;
    }
};

/* convenience function to create the inserter
 */
template <class Container>
inline asso_insert_iterator<Container> asso_inserter (Container& c)
{
    return asso_insert_iterator<Container>(c);
}


int main()
{
    set<int> coll;

    // create inserter for coll
    // - inconvenient way
    asso_insert_iterator<set<int> > iter(coll);

    // insert elements with the usual iterator interface
    *iter = 1;
    iter++;
    *iter = 2;
    iter++;
    *iter = 3;

    PRINT_ELEMENTS(coll);

    // create inserter for coll and insert elements
    // - convenient way
    asso_inserter(coll) = 44;
    asso_inserter(coll) = 55;

    PRINT_ELEMENTS(coll);

    // use inserter with an algorithm
    int vals[] = { 33, 67, -4, 13, 5, 2 };
    copy (vals, vals+(sizeof(vals)/sizeof(vals[0])),  // source
          asso_inserter(coll));                       // destination

    PRINT_ELEMENTS(coll);
}

1 2 3
1 2 3 44 55
-4 1 2 3 5 13 33 44 55 67