C++ Tutorial/set multiset/multiset

Add elements into an integer set and output all added elements

<source lang="cpp">/* 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.
*/

1. include <iostream>
2. include <set>
3. include <algorithm>
4. include <iterator>

using namespace std; int main() {

   /* type of the collection:
    * - duplicates allowed
    * - elements are integral values
    * - descending order
    */
   typedef multiset<int,greater<int> > IntSet;
   IntSet coll1;        // empty multiset container
   // insert elements in random order
   coll1.insert(4);
   coll1.insert(3);
   coll1.insert(5);
   coll1.insert(1);
   coll1.insert(6);
   coll1.insert(2);
   coll1.insert(5);
   // iterate over all elements and print them
   IntSet::iterator pos;
   for (pos = coll1.begin(); pos != coll1.end(); ++pos) {
       cout << *pos << " ";
   }
   cout << endl;

}</source>

6 5 5 4 3 2 1

Assign elements to another multiset with ascending order

<source lang="cpp">/* 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.
*/

1. include <iostream>
2. include <set>
3. include <algorithm>
4. include <iterator>

using namespace std; int main() {

   /* type of the collection:
    * - duplicates allowed
    * - elements are integral values
    * - descending order
    */
   typedef multiset<int,greater<int> > IntSet;
   IntSet coll1;        // empty multiset container
   // insert elements in random order
   coll1.insert(4);
   coll1.insert(3);
   coll1.insert(5);
   coll1.insert(1);
   coll1.insert(6);
   coll1.insert(2);
   coll1.insert(5);
   // iterate over all elements and print them
   IntSet::iterator pos;
   for (pos = coll1.begin(); pos != coll1.end(); ++pos) {
       cout << *pos << " ";
   }
   cout << endl;
   // assign elements to another multiset with ascending order
   multiset<int> coll2(coll1.begin(),
                       coll1.end());
   
   // print all elements of the copy
   copy (coll2.begin(), coll2.end(),
         ostream_iterator<int>(cout," "));
   cout << endl;

}</source>

6 5 5 4 3 2 1
1 2 3 4 5 5 6

Define multiset< int, less< int > >

<source lang="cpp">#include <iostream>

1. include <set>
2. include <algorithm>

using namespace std; int main() {

  const int SIZE = 10;
  int a[ SIZE ] = { 7, 22, 9, 1, 18, 30, 100, 22, 85, 13 };
  typedef multiset< int, less< int > > ims;
  ims intMultiset;    // ims for "integer multiset"
  cout << "There are currently " << intMultiset.count( 15 )
       << " values of 15 in the multiset\n";   
  return 0;

}</source>

Initializing Associative Containers

<source lang="cpp">#include <algorithm>

1. include <functional>
2. include <iostream>
3. include <map>
4. include <set>
5. include <utility>

using namespace std; template <class T> void print(T& c){

  for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
     std::cout << *i << endl;
  }

} int main( ){

  const int num_cars = 6;
  const int year[num_cars] = { 1998, 1970, 1966, 2004, 1998, 1930 };
  const char* name[num_cars] = { "A", "B","C", "D", "E","F" };
  set<int> unique_years( year, year + num_cars );
  multiset<int> all_years( year, year + num_cars );
  print( unique_years );
  print( all_years );
  typedef map<string,int> Car_map;
  Car_map unique_cars;
  transform( name, name+num_cars, year,inserter( unique_cars, unique_cars.end() ),make_pair<string,int> );
  Car_map::const_iterator unique_cars_end = unique_cars.end();
  for( Car_map::const_iterator i = unique_cars.begin();i != unique_cars_end; ++i )
     cout << i->second << " " << i->first << endl;
  typedef multimap<string,int> Car_multimap;
  Car_multimap all_cars;
  transform( name, name+num_cars, year,inserter( all_cars, all_cars.end() ),make_pair<string,int> );
  Car_multimap::const_iterator all_cars_end = all_cars.end();
  for( Car_multimap::const_iterator i = all_cars.begin();i != all_cars_end; ++i )
     cout << i->second << " " << i->first << endl;

}</source>

Modify or Remove a Value in a Set or Multiset

<source lang="cpp">#include <iostream>

1. include <set>
2. include <vector>

using namespace std; template <class T> void print(T& c){

  for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
     std::cout << *i << endl;
  }

} int main(){

  const int num_grades = 11;
  const int grade[num_grades] = { 2, 5, 3, 8, 9, 9, 6, 3, 5, 9, 10 };
  set<int> unique( grade, grade+num_grades );
  multiset<int> all( grade, grade+num_grades );
  print( unique );
  print( all );
  const int wrong_grade = 9;
  const int right_grade = 10;
  if( unique.erase( wrong_grade ) == 1 ){
     if( unique.insert( right_grade ).second )
        cout << "Added new, unique grade of " << right_grade << endl;
     else
        cout << "Already have unique grade of " << right_grade << endl;
  }
  else
     cout << "No unique grade of " << wrong_grade << endl;
  multiset<int>::size_type num_wrong = all.erase( wrong_grade );
  if( num_wrong > 0 ) {
     vector<int> right( num_wrong, right_grade );
     all.insert( right.begin(), right.end() );
     unique.erase( wrong_grade );
     unique.insert( right_grade );
  }
  else
     cout << "No wrong grades of " << wrong_grade << endl;
  const int drop_grade = 5;
  multiset<int>::iterator spot = all.find( drop_grade );
  if( spot != all.end() ) {
     all.erase( spot );
     if( all.count( drop_grade ) == 0 )
        unique.erase( drop_grade );
  }
  else
     cout << "Couldn"t find a grade of " << drop_grade << endl;
  print( unique);
  print( all);

}</source>

Use std::copy to print all elements in a multiset

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. include <set> // multiset class-template definition
2. include <algorithm> // copy algorithm
3. include <iterator> // ostream_iterator

int main() {

  int a[ 10 ] = { 7, 22, 9, 1, 18, 30, 100, 22, 85, 13 };
  std::multiset< int, std::less< int > > intMultiset;
  std::ostream_iterator< int > output( cout, " " );
  // insert elements of array a into intMultiset
  intMultiset.insert( a, a + 10 );
  cout << "\nAfter insert, intMultiset contains:\n";
  std::copy( intMultiset.begin(), intMultiset.end(), output );

  cout << endl;
  return 0;

}</source>

After insert, intMultiset contains:
1 7 9 13 18 22 22 30 85 100