C++ Tutorial/map multimap/map iterator — различия между версиями

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Текущая версия на 10:28, 25 мая 2010

const_iterator for map

#include <map>
#include <iostream>
using namespace std;
typedef map <int, string> MAP_INT_STRING;
typedef multimap <int, string> MMAP_INT_STRING;
int main ()
{
    MAP_INT_STRING mapIntToString;
    mapIntToString.insert (MAP_INT_STRING::value_type (3, "Three"));
    MAP_INT_STRING::const_iterator iMapPairLocator;
    for ( iMapPairLocator = mapIntToString.begin (); iMapPairLocator != mapIntToString.end (); ++ iMapPairLocator )
    {
        cout << "Key: " << iMapPairLocator->first;
        cout << " Value: " << iMapPairLocator->second.c_str ();
        cout << endl;
    }
    return 0;
}

Create int string map and print all element pair

/* 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 <map>
#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

Cycle through the map in the reverse direction

#include <iostream>
#include <string>
#include <map>
#include <utility>
using namespace std;
void show(const char *msg, map<string, string> mp);
int main() {
  map<string, string> phonemap;
  phonemap["A"] = "444-555-1234";
  phonemap["B"] = "555-555-6576";
  phonemap["C"] = "555-555-9843";
  show("Here is the original map: ", phonemap);
  phonemap["B"] = "555 555-5555";
  cout << "New number: " << phonemap["B"] << endl;
  // Cycle through the map in the reverse direction.
  map<string, string>::reverse_iterator ritr;
  cout << "Display phonemap in reverse order:" << endl;
  for(ritr = phonemap.rbegin(); ritr != phonemap.rend(); ++ritr)
     cout << ritr->first << ": " << ritr->second << endl;
  return 0;
}
// Display the contents of a map<string, string> by using an iterator.
void show(const char *msg, map<string, string> mp) {
  map<string, string>::iterator itr;
  cout << msg << endl;
  for(itr=mp.begin(); itr != mp.end(); ++itr)
   cout << " " << itr->first << ": " << itr->second << endl;
  cout << endl;
}

Declare an iterator to a map<string, int>

#include <iostream>
#include <string>
#include <map>
using namespace std;
int main() {
  map<string, int> m;
  m.insert(pair<string, int>("A", 100));
  m.insert(pair<string, int>("G", 300));
  m.insert(pair<string, int>("B", 200));
  // Declare an iterator to a map<string, int>.
  map<string, int>::iterator itr;
  // Display the first element in m.
  itr = m.begin();
  cout << "Here is the first key/value pair in m: "
       << itr->first << ", " << itr->second << endl;
  return 0;
}

Declare a reverse iterator to a map<string, itr>

#include <iostream>
#include <string>
#include <map>
using namespace std;
int main() {
  map<string, int> m;
  m.insert(pair<string, int>("A", 100));
  m.insert(pair<string, int>("G", 300));
  m.insert(pair<string, int>("B", 200));
  // Declare an iterator to a map<string, int>.
  map<string, int>::iterator itr;
  // Declare a reverse iterator to a map<string, itr>.
  map<string, int>::reverse_iterator ritr;
  // show the contents of m in reverse order.
  cout << "The contents of m in reverse:\n";
  for(ritr=m.rbegin(); ritr != m.rend(); ++ritr)
    cout << "  " << ritr->first << ", " << ritr->second << endl;
  cout << endl;

  return 0;
}

Display the first element in map

#include <iostream>
#include <string>
#include <map>
using namespace std;
int main() {
  map<string, int> m;
  m.insert(pair<string, int>("A", 100));
  m.insert(pair<string, int>("G", 300));
  m.insert(pair<string, int>("B", 200));
  // Declare an iterator to a map<string, int>.
  map<string, int>::iterator itr;
  // Display the first element in m.
  itr = m.begin();
  cout << "Here is the first key/value pair in m: "
       << itr->first << ", " << itr->second << endl;
  return 0;
}

Display the last element in map

#include <iostream>
#include <string>
#include <map>
using namespace std;
int main() {
  map<string, int> m;
  m.insert(pair<string, int>("A", 100));
  m.insert(pair<string, int>("G", 300));
  m.insert(pair<string, int>("B", 200));
  // Declare an iterator to a map<string, int>.
  map<string, int>::iterator itr;
  // Display the last element in m.
  itr = m.end();
  --itr;
  cout << "Here is the last key/value pair in m: "
       << itr->first << ", " << itr->second << "\n\n";

  return 0;
}

Loop through map and print all the key/value pair

#include <iostream>
using std::cout;
using std::endl;
#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

reverse_iterator from map

#include <iostream>
#include <string>
#include <map>
#include <utility>
using namespace std;
void show(const char *msg, map<string, string> mp);
int main() {
  map<string, string> phonemap;
  phonemap["A"] = "444-555-1234";
  phonemap["B"] = "555-555-6576";
  phonemap["C"] = "555-555-9843";
  show("Here is the original map: ", phonemap);
  cout << endl;
  phonemap["B"] = "555 555-5555";
  cout << "New number for B: " << phonemap["B"] << endl;
  // Use find() to find a number.
  map<string, string>::iterator itr;
  itr = phonemap.find("A");
  if(itr != phonemap.end())
    cout << "Number for A is " << itr->second << endl;
  // Cycle through the map in the reverse direction.
  map<string, string>::reverse_iterator ritr;
  cout << "Display phonemap in reverse order:" << endl;
  for(ritr = phonemap.rbegin(); ritr != phonemap.rend(); ++ritr)
   cout << " " << ritr->first << ": " << ritr->second << endl;
  cout << endl;
  return 0;
}
// Display the contents of a map<string, string> by using an iterator.
void show(const char *msg, map<string, string> mp) {
  map<string, string>::iterator itr;
  cout << msg << endl;
  for(itr=mp.begin(); itr != mp.end(); ++itr)
   cout << " " << itr->first << ": " << itr->second << endl;
  cout << endl;
}

Use iterator to loop through map and print all elements

/* 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 <map>
#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
Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/map_multimap/map_iterator&oldid=2086»