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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     set_difference

      - A basic set operation for constructing a  sorted  differ-
     ence.



SYNOPSIS
     #include <algorithm>
     template <class InputIterator1, class InputIterator2,
              class OutputIterator>
      OutputIterator
          set_difference (InputIterator1 first1,
                         InputIterator1 last1,
                         InputIterator2 first2,
                         InputIterator2 last2,
                         OutputIterator result);
     template <class InputIterator1, class InputIterator2,
              class OutputIterator, class Compare>
      OutputIterator
          set_difference (InputIterator1 first1,
                         InputIterator1 last1,
                         InputIterator2 first2,
                         InputIterator2 last2,
                         OutputIterator result, Compare comp);



DESCRIPTION
     The set_difference algorithm constructs a sorted  difference
     that includes copies of the elements that are present in the
     range [first1, last1) but  are  not  present  in  the  range
     [first2,  last2).  It  returns  the  end  of the constructed
     range.

     As an example, assume we have the following two sets:

     1 2 3 4 5

     and

     3 4 5 6 7

     The result of applying set_difference is the set:

     1 2

     The result of set_difference  is  undefined  if  the  result
     range overlaps with either of the original ranges.

     set_difference assumes that the ranges are sorted using  the
     default  comparison operator less than (<), unless an alter-
     native comparison operator (comp) is provided.

     Use the set_symetric_difference algorithm to return a result
     that  contains  all  elements that are not in common between
     the two sets.



COMPLEXITY
     At most ((last1 - first1) + (last2 - first2)) *  2  -1  com-
     parisons are performed.



EXAMPLE
     //
     // set_diff.cpp
     //
     #include <algorithm>
     #include <set>
     #include <iostream>
     using namespace std;
     int main()
      {
     //Initialize some sets
     int a1[10] = {1,2,3,4,5,6,7,8,9,10};
     int a2[6]  = {2,4,6,8,10,12};
     set<int, less<int> > all(a1+0, a1+10), even(a2+0, a2+6),
                         odd;

     //Create an insert_iterator for odd
     insert_iterator<set<int, less<int> > >
                    odd_ins(odd, odd.begin());

     //Demonstrate set_difference
     cout << "The result of:" << endl << "{";
     copy(all.begin(),all.end(),
         ostream_iterator<int,char>(cout," "));
     cout << "} - {";
     copy(even.begin(),even.end(),
         ostream_iterator<int,char>(cout," "));
     cout << "} =" << endl << "{";
     set_difference(all.begin(), all.end(),
                   even.begin(), even.end(), odd_ins);
     copy(odd.begin(),odd.end(),
         ostream_iterator<int,char>(cout," "));
     cout << "}" << endl << endl;
     return 0;
      }

     Program Output



     The result of:
     {1 2 3 4 5 6 7 8 9 10 } - {2 4 6 8 10 12 } =
     {1 3 5 7 9 }



WARNINGS
     If your compiler does not support default  template  parame-
     ters,  then  you  always need to supply the Compare template
     argument and the Allocator template argument. For  instance,
     you need to write:

     set<int, less<int> allocator<int> >

     instead of:

     set<int>

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.



SEE ALSO
     includes,         set,          set_union,_set_intersection,
     set_symmetric_difference

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