//文件名:CHAPTER9-3.cpp
#include <set>
#include <iostream>
#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
#endif
int main( )
{
   set <int> s1;
   set <int>::iterator s1_Iter;
   set <int>::const_iterator s1_cIter;
   s1.insert( 1 );
   s1.insert( 2 );
   s1.insert( 3 );
   s1_Iter = s1.begin( );
   cout << "The first element of s1 is " << *s1_Iter << endl;
   s1_Iter = s1.begin( );
   s1.erase( s1_Iter );
   // The following 2 lines would err because the iterator is const
   // s1_cIter = s1.begin( );
   // s1.erase( s1_cIter );
   s1_cIter = s1.begin( );
   cout << "The first element of s1 is now " << *s1_cIter << endl;
}