5. std::pair data members

• In mathematics, a tuple is a sequence of values, or tuple components, each component of a specified type. A tuple containing n components is known as an n-tuple.

  
      std::pair< typename T, typename U >
  
  

• Thus, std::pair supports duples.

• A pair has two public members, first and second.

  
      template< typename T, typename U >
      struct pair {
          typedef T first_type;
          typedef U second_type;
          T first;
          U second;
  
          pair(); // default constructor
  
          // construct from specified values:
          pair( T const& x, U const& y );
  
          // construct from compatible pair:
          template< typename V, typename W > pair( pair<V, W> const& pr );
      };