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set::lower_bound, set::upper_bound, and set::equal_range 

Illustrates how to use the set::lower_bound, set::upper_bound, and set::equal_range Standard Template Library (STL) functions in Visual C++.


template<class _K, class _Pr, class _A>
   class set 
   {
      public:
      // Function 1:
      const_iterator lower_bound(const _K& _Kv) const;
      // Function 2:
      const_iterator upper_bound(const _K& _Kv) const;
      // Function 3:
      _Paircc equal_range(const _K& _Kv) const;
   }

NoteNote

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The lower_bound function returns an iterator to the earliest element in the controlled sequence that has a key that does not match the value passed to the lower_bound function. The upper_bound function returns an iterator to the earliest element in the controlled sequence that has a key matching the value passed to the upper_bound function. If no such element exists, the function returns end. In both cases, the function set::key_comp(key, x) is used to determine if the keys match. The equal_range function returns a pair value, where .First is the result of the lower_bound function, and .second is the result of the upper_bound function.

// SetBoundRange.cpp
// compile with: /EHsc
//
//      Illustrates how to use the lower_bound function to get an
//      iterator to the earliest element in the controlled sequence
//      that has a key that does not match the value passed to the
//      function. It also illustrates how to use the upper_bound
//      function to get an iterator to the earliest element in the
//      controlled sequence that has a key that matches the value
//      passed to the function. The last thing it illustrates is
//      how to use the equal_range function to get a pair value that
//      contains the lower_bound and upper_bound results of the key.
//
// Functions:
//
//    lower_bound  Returns an iterator whose value does not match the
//                 key passed to the function, or end() if no such
//                 element exists.
//    upper_bound  Returns an iterator whose value matches the key
//                 passed to the function, or end() if no such element
//                 exists.
//    equal_range  Returns a pair of (lower_bound,upper_bound).
//////////////////////////////////////////////////////////////////////

#pragma warning(disable:4786)
#include <set>
#include <iostream>

using namespace std ;

typedef set<int> SET_INT;

int main() {
  SET_INT s1;
  SET_INT::iterator i;
  cout << "s1.insert(5)" << endl;
  s1.insert(5);
  cout << "s1.insert(10)" << endl;
  s1.insert(10);
  cout << "s1.insert(15)" << endl;
  s1.insert(15);
  cout << "s1.insert(20)" << endl;
  s1.insert(20);
  cout << "s1.insert(25)" << endl;
  s1.insert(25);

  cout << "s1 -- starting at s1.lower_bound(12)" << endl;
// prints: 15,20,25
  for (i=s1.lower_bound(12);i!=s1.end();i++)
     cout << "s1 has " << *i << " in its set." << endl;

  cout << "s1 -- starting at s1.lower_bound(15)" << endl;
// prints: 15,20,25
  for (i=s1.lower_bound(15);i!=s1.end();i++)
     cout << "s1 has " << *i << " in its set." << endl;

  cout << "s1 -- starting at s1.upper_bound(12)" << endl;
// prints: 15,20,25
  for (i=s1.upper_bound(12);i!=s1.end();i++)
     cout << "s1 has " << *i << " in its set." << endl;

  cout << "s1 -- starting at s1.upper_bound(15)" << endl;
// prints: 20,25
  for (i=s1.upper_bound(15);i!=s1.end();i++)
     cout << "s1 has " << *i << " in its set." << endl;

  cout << "s1 -- s1.equal_range(12)" << endl;
// does not print anything
  for (i=s1.equal_range(12).first;i!=s1.equal_range(12).second;i++)
     cout << "s1 has " << *i << " in its set." << endl;

  cout << "s1 -- s1.equal_range(15)" << endl;
// prints: 15
  for (i=s1.equal_range(15).first;i!=s1.equal_range(15).second;i++)
     cout << "s1 has " << *i << " in its set." << endl;
}

s1.insert(5)
s1.insert(10)
s1.insert(15)
s1.insert(20)
s1.insert(25)
s1 -- starting at s1.lower_bound(12)
s1 has 15 in its set.
s1 has 20 in its set.
s1 has 25 in its set.
s1 -- starting at s1.lower_bound(15)
s1 has 15 in its set.
s1 has 20 in its set.
s1 has 25 in its set.
s1 -- starting at s1.upper_bound(12)
s1 has 15 in its set.
s1 has 20 in its set.
s1 has 25 in its set.
s1 -- starting at s1.upper_bound(15)
s1 has 20 in its set.
s1 has 25 in its set.
s1 -- s1.equal_range(12)
s1 -- s1.equal_range(15)
s1 has 15 in its set.

Header: <set>

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