Article ID: 158573 - Last Review: July 15, 2005 - Revision: 4.1

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

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This article was previously published under Q158573
Note Microsoft Visual C++ NET (2002) supported both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. The information in this article applies to unmanaged Visual C++ code only.

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SUMMARY

The following sample code illustrates how to use the set::key_comp and set::value_comp STL functions in Visual C++.
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MORE INFORMATION

Required header

   <set>
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Prototype

   template<class _K, class _Pr, class _A>
   class set {
   public:
   // Function 1:

      key_compare key_comp() const;

   // Function 2:
      value_compare value_comp() const;
   }
Note The class/parameter names in the prototype may not match the version in the header file. Some have been modified to improve readability.
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Description

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 key_comp returns.
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Sample code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: -GX
// 
// SetComp.cpp:
//      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).
// 
// Written by Derek Jamison
// of Microsoft Technical Support,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

#pragma warning(disable:4786)

#include <set>
#include <iostream>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef set<int,less<int>,allocator<int> > SET_INT;

void truefalse(int x)

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

void 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
}
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Program output

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
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REFERENCES

For the same topic about set::(key_, value_)comp, visit the following MSDN Web site: http://msdn.microsoft.com/en-us/library/w9bd5c6s(VS.71).aspx (http://msdn.microsoft.com/en-us/library/w9bd5c6s(VS.71).aspx)
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APPLIES TO
  • The Standard C++ Library, when used with:
    • Microsoft Visual C++ 4.2 Enterprise Edition
    • Microsoft Visual C++ 5.0 Enterprise Edition
    • Microsoft Visual C++ 6.0 Enterprise Edition
    • Microsoft Visual C++ 4.2 Professional Edition
    • Microsoft Visual C++ 5.0 Professional Edition
    • Microsoft Visual C++ 6.0 Professional Edition
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
    • Microsoft Visual C++ .NET 2002 Standard Edition
    • Microsoft Visual C++ .NET 2003 Standard Edition
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Keywords: 
kbfunctions kbhowto kbcode kbinfo kbstl kbtemplate KB158573
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