C++ Tutorial/map multimap/pair

Assign value directly to first and second

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

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

using namespace std; int main(int argc, char** argv) {

 pair<string, int> myPair("hello", 5), myOtherPair;
 myOtherPair.first = "hello";
 myOtherPair.second = 6;
 return (0);

}</source>

Create a pair object that holds the result of insert()

<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;
 // 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>("Jay", "555-9999"));
 if(result.second) cout << "Jay added.\n";
 show("phonemap after adding Jay: ", 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>

Create a pair object that will contain the result of a call to insert()

<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>

Default constructor for pair

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

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

using namespace std; int main(int argc, char** argv) {

 pair<string, int> myPair("hello", 5), myOtherPair;
 return (0);

}</source>

Sort a vector of pairs

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

1. include <iostream>
2. include <iterator>
3. include <string>
4. include <vector>
5. include <utility>

using namespace std; typedef pair<int,string> Pair; inline bool less_than_second( const Pair& b1, const Pair& b2 ){

  return b1.second < b2.second;

} int main(){

  const char* names[] = { "A","B", "C", "D","E" };
  const int values[] = { 18, 20, 26, 30, 41 };
  const int num_pairs = sizeof( names ) / sizeof( names[0] );
  vector<Pair> pair( num_pairs );
  transform( values, values+num_pairs, names,pair.begin(), make_pair<int,string> );
  sort( pair.begin(), pair.end() );
  sort( pair.begin(), pair.end(), less_than_second );
  vector<Pair>::const_iterator pair_end = pair.end();
  for( vector<Pair>::const_iterator i = pair.begin();
     i != pair_end; ++i )
  cout << i->second << " - $" << i->first << " values\n";

}</source>

Use make_pair() function to create a pair

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

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

using namespace std; int main(int argc, char** argv){

 pair<string, int> myPair("hello", 5), myOtherPair;
 myOtherPair.first = "hello";
 myOtherPair.second = 6;
 pair<string, int> myThirdPair(myOtherPair);
 pair<int, int> aPair = make_pair(5, 10);
 return (0);

}</source>

Use operator of equal (=)

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

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

using namespace std; int main(int argc, char** argv) {

 pair<string, int> myPair("hello", 5), myOtherPair;
 myOtherPair.first = "hello";
 myOtherPair.second = 6;
 pair<string, int> myThirdPair(myOtherPair);
 if (myOtherPair == myThirdPair) {
   cout << "myOtherPair is equal to myThirdPair\n";
 } else {
   cout << "myOtherPair is not equal to myThirdPair\n";
 }
 pair<int, int> aPair = make_pair(5, 10);
 return (0);

}</source>

Use operator of less than (

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

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

using namespace std; int main(int argc, char** argv){

 pair<string, int> myPair("hello", 5), myOtherPair;
 myOtherPair.first = "hello";
 myOtherPair.second = 6;
 pair<string, int> myThirdPair(myOtherPair);
 if (myPair < myOtherPair) {
   cout << "myPair is less than myOtherPair\n";
 } else {
   cout << "myPair is greater than or equal to myOtherPair\n";
 }
 return (0);

}</source>

Using a Pair to store int and string

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

1. include <iostream>
2. include <iterator>
3. include <string>
4. include <vector>
5. include <utility>

using namespace std; typedef pair<int,string> Pair; inline bool less_than_second( const Pair& b1, const Pair& b2 ){

  return b1.second < b2.second;

} int main( ) {

  const char* names[] = { "A","B", "C", "D","E" };
  const int values[] = { 18, 20, 26, 30, 41 };
  const int num_pairs = sizeof( names ) / sizeof( names[0] );
  vector<Pair> pair( num_pairs );
  transform( values, values+num_pairs, names,pair.begin(), make_pair<int,string> );
  if( pair[1].first > pair[3].first )
     cout << pair[1].second << " > " << pair[3].second << endl;
  else if( pair[1].first == pair[3].first )
     cout << pair[1].second << " == " << pair[3].second << endl;
  else
     cout << pair[1].second << " < " << pair[3].second << endl;
  sort( pair.begin(), pair.end() );
  vector<Pair>::const_reverse_iterator pair_rend = pair.rend();
  
  for( vector<Pair>::const_reverse_iterator i= pair.rbegin(); i != pair_rend; ++i )
     cout << i->first << " - " << i->second;
  sort( pair.begin(), pair.end(), less_than_second );
  vector<Pair>::const_iterator pair_end = pair.end();
  for( vector<Pair>::const_iterator i = pair.begin();
     i != pair_end; ++i )
     cout << i->second << " - $" << i->first << " values\n";

}</source>

Using copy constructor to create another pair

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

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

using namespace std; int main(int argc, char** argv) {

 pair<string, int> myPair("hello", 5), myOtherPair;
 // assign directly to first and second
 myOtherPair.first = "hello";
 myOtherPair.second = 6;
 // copy construcor
 pair<string, int> myThirdPair(myOtherPair);
 return (0);

}</source>

Vector of pair

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

1. include <iostream>
2. include <iterator>
3. include <string>
4. include <vector>
5. include <utility>

using namespace std; typedef pair<int,string> Pair; inline bool less_than_second( const Pair& b1, const Pair& b2 ){

  return b1.second < b2.second;

} int main( ) {

  const char* names[] = { "A","B", "C", "D","E" };
  const int values[] = { 18, 20, 26, 30, 41 };
  const int num_pairs = sizeof( names ) / sizeof( names[0] );
  vector<Pair> pair( num_pairs );
  transform( values, values+num_pairs, names,pair.begin(), make_pair<int,string> );
  sort( pair.begin(), pair.end() );
  vector<Pair>::const_reverse_iterator pair_rend = pair.rend();
  
  for( vector<Pair>::const_reverse_iterator i= pair.rbegin(); i != pair_rend; ++i )
     cout << i->first << " - " << i->second;
  sort( pair.begin(), pair.end(), less_than_second );
  vector<Pair>::const_iterator pair_end = pair.end();
  for( vector<Pair>::const_iterator i = pair.begin();
     i != pair_end; ++i )
  cout << i->second << " - $" << i->first << " values\n";

}</source>