set.insert returns pair: p.first represents location and p.second represents the successfulness : set insert « set multiset « C++ Tutorial

1. C++ Tutorial
2. set multiset
3. set insert

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

#include <set>

#include <algorithm>
#include <iterator> // ostream_iterator

int main()
{
   double a[ 5 ] = { 2.1, 4.2, 9.5, 2.1, 3.7 };
   std::set< double, std::less< double > > doubleSet( a, a + 5 );;
   std::ostream_iterator< double > output( cout, " " );

   // p represents pair containing const_iterator and bool
   std::pair< std::set< double, std::less< double > >::const_iterator, bool > p;

   p = doubleSet.insert( 13.8 ); // value not in set
   cout << *( p.first ) << ( p.second ? " was" : " was not" ) << " inserted";
   cout << "\ndoubleSet contains: ";
   std::copy( doubleSet.begin(), doubleSet.end(), output );


   cout << endl;
   return 0;
}

13.8 was inserted
doubleSet contains: 2.1 3.7 4.2 9.5 13.8