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set::key_comp and set::value_comp 

Illustrates how to use the set::key_comp and set::value_comp Standard Template Library (STL) functions in Visual C++.


template<class _K, class _Pr, class _A>
   class set 
   {
      public:
      // Function 1:
      key_compare key_comp( ) const;
      // Function 2:
      value_compare value_comp( ) 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 key_comp function returns the stored function object that determines the order of elements in the controlled sequence. The value_comp function returns the same function that the key_comp function returns.

// SetComp.cpp
// compile with: /EHsc
//
//      Illustrates how to use the key_comp function to obtain a
//      function pointer that is the stored function object that
//      determines the order of elements in the controlled sequence.
//      It also illustrates how to use the value_comp function to
//      obtain a function pointer that is the stored function object
//      that determines the order of the elements in the controlled
//      sequence (same as key_comp result).
//
// Functions:
//
//    key_comp     Returns a function pointer to the function that
//                 determines the order of elements in the controlled
//                 sequence.
//    value_comp   Returns a function pointer to the function that
//                 determines the order of elements in the controlled
//                 sequence (same as key_comp).
//////////////////////////////////////////////////////////////////////

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

using namespace std ;

typedef set<int> SET_INT;

void truefalse(int x)
{
  cout << (x?"True":"False") << endl;
}

int main() {
  SET_INT s1;

  cout << "s1.key_comp()(8,10) returned ";
  truefalse(s1.key_comp()(8,10));  // True

  cout << "s1.value_comp()(8,10) returned ";
  truefalse(s1.value_comp()(8,10));  // True

  cout << "s1.key_comp()(10,8) returned ";
  truefalse(s1.key_comp()(10,8));  // False

  cout << "s1.value_comp()(10,8) returned ";
  truefalse(s1.value_comp()(10,8));  // False

  cout << "s1.key_comp()(8,8) returned ";
  truefalse(s1.key_comp()(8,8));  // False

  cout << "s1.value_comp()(8,8) returned ";
  truefalse(s1.value_comp()(8,8));   // False
}
s1.key_comp()(8,10) returned True
s1.value_comp()(8,10) returned True
s1.key_comp()(10,8) returned False
s1.value_comp()(10,8) returned False
s1.key_comp()(8,8) returned False
s1.value_comp()(8,8) returned False

Header: <set>

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