INFO: (key_, value_)comp Function

ID: Q158573

The information in this article applies to:

The Standard C++ Library, used with:
- Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0, 6.0

SUMMARY

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

MORE INFORMATION

Required Header


   <set>

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.

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.

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
}

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

REFERENCES

Visual C++ Books Online: Visual C++ Books; C/C++; Standard C++ Library Reference

Additional query words: STL STLSample value_comp key_comp

Keywords : kbcode kbVC420 kbVC500 kbVC600 kbDSupport STLIss
Version : winnt:4.2,5.0,6.0
Platform : winnt
Issue type : kbinfo