C++/Map Multimap/map iterator

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const_iterator for map if integer and user-define object

<source lang="cpp">

  1. include <algorithm>
  2. include <functional>
  3. include <iomanip>
  4. include <iostream>
  5. include <map>
  6. include <string>
  7. include <utility>
  8. include <vector>

using namespace std; class PC { 

  public:
  enum PC_type { Dell, HP, IBM, Compaq };
  PC( PC_type appliance = Dell, int model = 220,
     int serial = 0 );
  bool operator<( const PC& rhs ) const;
  PC_type appliance() const;
  int model() const;
  string name() const;
  void print() const;
  int serial() const;
  private:
  PC_type appliance_;
  int model_;
  int serial_;

}; inline PC::PC( PC::PC_type appliance, int model, 

  int serial )
  : appliance_( appliance ), model_( model ), serial_( serial )

{} // empty inline bool PC::operator<( const PC& rhs ) const { return appliance() < rhs.appliance() || 

  ( appliance() == rhs.appliance() && model() < rhs.model() );

} inline PC::PC_type PC::appliance() const { return appliance_; } inline int PC::model() const { return model_; } string PC::name() const { 

  string what;
  switch( appliance() )
  {
     case Dell:   what = "Dell";               break;
     case HP:     what = "HP";                 break;
     case IBM:    what = "IBM";                break;
     case Compaq: what = "Compaq";             break;
     default:     what = "Unknown appliance";  break;
  }
  return what;

} inline void PC::print() const { 

  char oldfill = cout.fill();
  cout << name() << " - Model "
       << model() << ", Serial number " 
       << serial() << endl;

} inline int PC::serial() const { return serial_; } bool greater_model( const pair<PC::PC_type,PC> p,int min_model ); int main( ) { 

  const PC::PC_type kind[] = { PC::IBM,PC::Dell,PC::HP};
  int num_appliances = 3;
  vector<PC> v;
  for( int i = 0; i < 3; ++i )
     v.push_back( PC( kind[i], i, i ) );
  map<int,PC> sold;
  transform( kind, kind+num_appliances, v.begin(),inserter( sold, sold.end() ),make_pair<int,PC> );
  map<int,PC>::const_iterator sold_end = sold.end();
  map<int,PC>::const_iterator site;
  for( site = sold.begin(); site != sold_end; ++site )
     site->second.print();

} inline bool greater_model( const pair<PC::PC_type,PC> p,int min_model ) { return p.second.model() >= min_model; } 



 </source>


const_reverse_iterator from a map

<source lang="cpp">

  1. include <algorithm>
  2. include <functional>
  3. include <iomanip>
  4. include <iostream>
  5. include <map>
  6. include <string>
  7. include <utility>
  8. include <vector>

using namespace std; class PC { 

  public:
  enum PC_type { Dell, HP, IBM, Compaq };
  PC( PC_type appliance = Dell, int model = 220,
     int serial = 0 );
  bool operator<( const PC& rhs ) const;
  PC_type appliance() const;
  int model() const;
  string name() const;
  void print() const;
  int serial() const;
  private:
  PC_type appliance_;
  int model_;
  int serial_;

}; inline PC::PC( PC::PC_type appliance, int model, 

  int serial )
  : appliance_( appliance ), model_( model ), serial_( serial )

{} // empty inline bool PC::operator<( const PC& rhs ) const { return appliance() < rhs.appliance() || 

  ( appliance() == rhs.appliance() && model() < rhs.model() );

} inline PC::PC_type PC::appliance() const { return appliance_; } inline int PC::model() const { return model_; } string PC::name() const { 

  string what;
  switch( appliance() )
  {
     case Dell:    what = "Dell";               break;
     case HP:      what = "HP";                 break;
     case IBM:     what = "IBM";                break;
     case Compaq:  what = "Compaq";             break;
     default:      what = "Unknown appliance";  break;
  }
  return what;

} inline void PC::print() const { 

  char oldfill = cout.fill();
  cout << name() << " - Model "
       << model() << ", Serial number "
       << serial() << endl;

} inline int PC::serial() const { return serial_; } bool greater_model( const pair<PC::PC_type,PC> p,int min_model ); int main( ) { 

  const PC::PC_type kind[] = { PC::IBM,
     PC::IBM, PC::Dell, PC::HP,
     PC::HP, PC::HP };
  const int num_appliances = 3;
  vector<PC> v;
  for( int i = 0; i < num_appliances; ++i )
     v.push_back( PC( kind[i], i, i ) );
  map<int,PC> sold;
  transform( kind, kind+num_appliances, v.begin(),inserter( sold, sold.end() ),make_pair<int,PC> );
  map<int,PC>::const_iterator sold_end = sold.end();
  map<int,PC>::const_iterator site;
  for( site = sold.begin(); site != sold_end; ++site )
     site->second.print();
  map<int,PC>::const_reverse_iterator reverse_site;
  map<int,PC>::const_reverse_iterator sold_rend = sold.rend();
  const PC::PC_type desired_type = PC::IBM;
  for( reverse_site = sold.rbegin(); reverse_site != sold_rend;++reverse_site )
     if( reverse_site->second.appliance() == desired_type )
        break;
  if( reverse_site != sold_rend )
     reverse_site->second.print();
  else
     cout << "No IBMs sold\n";

} inline bool greater_model( const pair<PC::PC_type,PC> p,int min_model ) { return p.second.model() >= min_model; } 



 </source>


Create int string map and print all element pair

<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 <map>
  3. include <string>

using namespace std; int main() { 

   // type of the collection
   typedef multimap<int,string> IntStringMMap;
   IntStringMMap coll;        // container for int/string values
   // insert some elements in arbitrary order
   // - a value with key 1 gets inserted twice
   coll.insert(make_pair(5,"tagged"));
   coll.insert(make_pair(2,"a"));
   coll.insert(make_pair(1,"this"));
   coll.insert(make_pair(4,"of"));
   coll.insert(make_pair(6,"strings"));
   coll.insert(make_pair(1,"is"));
   coll.insert(make_pair(3,"multimap"));
   /* print all element values
    * - iterate over all elements
    * - element member second is the value
    */
   IntStringMMap::iterator pos;
   for (pos = coll.begin(); pos != coll.end(); ++pos) {
       cout << pos->second << " ";
   }
   cout << endl;

} 

/*

this is a multimap of tagged strings 

*/       
   
   
 </source>


Get iterator from a map

<source lang="cpp">

  1. include <iostream>
  2. include <map>

using namespace std;

int main() { 

 map<char, int> m;
 int i;
  
 for(i=0; i<26; i++) {
   m.insert(pair<char, int>("A"+i, 65+i));
 }
  
 char ch;
 cout << "Enter key: ";
 cin >> ch;
  
 map<char, int>::iterator p;

 p = m.find(ch);
 if(p != m.end())
   cout << "Its ASCII value is  " << p->second;
 else
   cout << "Key not in map.\n";
  
 return 0;

} 


 </source>


Loop through map and print all the key/value pair

<source lang="cpp">

  1. include <iostream>

using std::cout; using std::endl;

  1. include <map> // map class-template definition

int main() { 

  std::map< int, double, std::less< int > > pairs;
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 15, 2.7 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 30, 111.11 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 0, 1010.1 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 10, 22.22 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 25, 33.333 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 0, 77.54 ) ); // dup ignored
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 20, 9.345 ) );
  pairs.insert( std::map< int, double, std::less< int > >::value_type( 15, 99.3 ) ); // dup ignored
  cout << "pairs contains:\nKey\tValue\n";
  // use const_iterator to walk through elements of pairs
  for ( std::map< int, double, std::less< int > >::const_iterator iter = pairs.begin();
     iter != pairs.end(); ++iter )
     cout << iter->first << "\t" << iter->second << "\n";
  cout << endl;
  return 0;

} /* pairs contains: Key Value 0 1010.1 10 22.22 15 2.7 20 9.345 25 33.333 30 111.11 

*/        
   
   
 </source>


Map Iterators

<source lang="cpp">

  1. include <map>
  2. include <iostream>

using namespace std; class Data { public: 

 Data(int val = 0) { mVal = val; }
 int getVal() const { return mVal; }
 void setVal(int val) {mVal = val; }

protected: 

 int mVal;

}; int main(int argc, char** argv) { 

 map<int, Data> dataMap;
 dataMap[1] = Data(4);
 dataMap[1] = Data(6);
 for (map<int, Data>::iterator it = dataMap.begin();
      it != dataMap.end(); ++it) {
   cout << it->second.getVal() << endl;
 }
 return (0);

} 


 </source>


Use iterator to loop through map and print all 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 <map>
  3. include <string>

using namespace std; int main() { 

   /* type of the container:
    * - map: elements key/value pairs
    * - string: keys have type string
    * - float: values have type float
    */
   typedef map<string,float> StringFloatMap;
   StringFloatMap coll;
   // insert some elements into the collection
   coll["VAT"] = 0.15;
   coll["Pi"] = 3.1415;
   coll["an arbitrary number"] = 4983.223;
   coll["Null"] = 0;
   /* print all elements
    * - iterate over all elements
    * - element member first is the key
    * - element member second is the value
    */
   StringFloatMap::iterator pos;
   for (pos = coll.begin(); pos != coll.end(); ++pos) {
       cout << "key: \"" << pos->first << "\" "
            << "value: " << pos->second << endl;
   }

} 

/*

key: "Null" value: 0 key: "Pi" value: 3.1415 key: "VAT" value: 0.15 key: "an arbitrary number" value: 4983.22 

*/       
   
   
 </source>


Use while to loop through a map

<source lang="cpp">

  1. include <map>
  2. include <iostream>
  3. include <string>

using namespace std; typedef map<string, int> STRING2INT; int main(void) { 

   STRING2INT DateMap;
   STRING2INT::iterator DateIterator;
   string DateBuffer;
   DateMap["January"] = 1;
   DateMap["February"] = 2;
   DateMap["March"] = 3;
   DateMap["April"] = 4;
   DateMap["May"] = 5;
   DateMap["June"] = 6;
   DateMap["July"] = 7;
   DateMap["August"] = 8;
   DateMap["September"] = 9;
   DateMap["October"] = 10;
   DateMap["November"] = 11;
   DateMap["December"] = 12;
   DateIterator = DateMap.end();
   while(DateIterator == DateMap.end())
    {
       cout << "Enter a Month :";
       cin >> DateBuffer;
       if((DateIterator = DateMap.find(DateBuffer)) != DateMap.end())
           cout << (*DateIterator).first << " is Month Number "
                << (*DateIterator).second << endl;
       else
           cout << "Enter a Valid Month (example: March)" << endl;
    }

} 


 </source>
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