C++ Tutorial/map multimap/map insert

Duplicate keys are not allowed in a map

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

1. include <string>
2. include <map>
3. 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;
 // Now, change the phone number for Ken.
 phonemap["B"] = "555 555-5555";
 cout << "New number for Ken: " << phonemap["Ken"] << "\n\n";
 // Create a pair object that will contain the result of a call to insert().
 pair<map<string, string>::iterator, bool> result;
 // Duplicate keys are not allowed, as the following proves.
 result = phonemap.insert(pair<string, string>("B", "555-1010"));
 if(result.second) 
    cout << "Duplicate added! Error!";
 else 
    cout << "Duplicate not allowed.\n";
 show("phonemap after attempt to add duplicate key: ", phonemap);
 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;

}</source>

Insert a pair object directly

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

1. 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 (pair <int, string> (1000, "One Thousand"));
   cout << "The map contains " << mapIntToString.size ();
   cout << " key-value pairs. " << endl;
   cout << "The elements in the map are: " << endl;
   return 0;

}</source>

Insert a pair using function make_pair

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

1. 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 (make_pair (-1, "Minus One"));
   cout << "The map contains " << mapIntToString.size ();
   cout << " key-value pairs. " << endl;
   cout << "The elements in the map are: " << endl;
   return 0;

}</source>

Insert characters into map.

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

1. include <string>
2. 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));
 return 0;

}</source>

Insert key-value pairs into the map using value_type

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

1. 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;
   // Insert key-value pairs into the map using value_type
   mapIntToString.insert (MAP_INT_STRING::value_type (3, "Three"));
   cout << "The map contains " << mapIntToString.size ();
   cout << " key-value pairs. " << endl;
   cout << "The elements in the map are: " << endl;
   return 0;

}</source>

Insert using an array-like syntax for inserting key-value pairs

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

1. 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;
   // Insert using an array-like syntax for inserting key-value pairs
   mapIntToString [1000000] = "One Million";
   cout << "The map contains " << mapIntToString.size ();
   cout << " key-value pairs. " << endl;
   cout << "The elements in the map are: " << endl;
   return 0;

}</source>

Insert value pair to map

<source lang="cpp">#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;

}</source>

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

Use insert() to add an entry

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

1. include <string>
2. include <map>
3. 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;
 // Create a pair object that will contain the result of a call to insert().
 pair<map<string, string>::iterator, bool> result;
 // Use insert() to add an entry.
 result = phonemap.insert(pair<string, string>("J", "555-9999"));
 if(result.second) cout << "J added.";
 show("phonemap after adding J: ", phonemap);
 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;

}</source>

use subscript operator to write value to a map

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

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

using namespace std; int main( ) {

  const char* word[] = { "A", "B", "C", "D","E" };
  const char* clue[] = { "a", "b","c", "d","e" };
  map<string,string> dictionary1;
  transform( word, word+sizeof(word)/sizeof(word[0]), clue,inserter( dictionary1, dictionary1.end() ),make_pair<string,string> );
  cout << "There are " << dictionary1.size() << " words in the dictionary\n\n";
  cout << "The clue for POPS is \"" << dictionary1["POPS"] << "\"\n"
     << "The clue for TAT is \"" << dictionary1["TAT"] << "\"\n"
     << "The clue for ESPO0 is \"" << dictionary1["ESPO0"] << "\"\n";
  cout << "\nThere are " << dictionary1.size() << " words in the dictionary\n\n";
  // use subscript operator to write value
  dictionary1["ESPO0"] = "Typo in name";
  cout << "The clue for ESPO0 is \"" << dictionary1["ESPO0"] << "\"";

}</source>