Microsoft KB Archive/156993

= INFO: STL Sample for the Predicate Version of nth_element Function =

Article ID: 156993

Article Last Modified on 9/23/2003

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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</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2002 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2003 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q156993

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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 sample code below illustrates how to use the predicate version of the nth_element STL function in Visual C++.

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Prototype
template<class RandomAccessIterator, class Compare> inline void nth_element(RandomAccessIterator first,

RandomAccessIterator nth, RandomAccessIterator last, Compare compare) NOTE: The class/parameter names in the prototype do not match the original version in the header file. They have been modified to improve readability.

Description
The nth_element algorithm partitions the sequence [first..last) on the value referenced by nth. All the elements less than or equal to the value are placed before value and all elements greater than value are placed after value in the sequence.

The predicate version of nth_element uses the compare function for comparisons.

Sample Code
////////////////////////////////////////////////////////////////////// // // Compile options needed: /GX // // nth_element.cpp : Illustrates how to use the predicate version //                  of the nth_element function. // // Functions: // //   nth_element : Partition the elements in a sequence by its nth //                 element. // // Written by Kalindi Sanghrajka // of Microsoft Product Support Services, // Software Core Developer Support. // Copyright (c) 1996 Microsoft Corporation. All rights reserved. //////////////////////////////////////////////////////////////////////

// disable warning C4786: symbol greater than 255 character, // okay to ignore


 * 1) pragma warning(disable: 4786)


 * 1) include
 * 2) include
 * 3) include
 * 4) include

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

void main

{

const int VECTOR_SIZE = 8 ;

// Define a template class vector of int typedef vector<int, allocator > IntVector ;

//Define an iterator for template class vector of strings typedef IntVector::iterator IntVectorIt ;

IntVector Numbers(VECTOR_SIZE) ;

IntVectorIt start, end, it ;

// Initialize vector Numbers Numbers[0] = 4 ; Numbers[1] = 10; Numbers[2] = 70 ; Numbers[3] = 30 ; Numbers[4] = 10; Numbers[5] = 69 ; Numbers[6] = 96 ; Numbers[7] = 100;

start = Numbers.begin ;  // location of first // element of Numbers

end = Numbers.end ;      // one past the location // last element of Numbers

cout << "Before calling nth_element:\n" << endl ;

// print content of Numbers cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ;

// partition the elements by the 4th element nth_element(start, start+4, end, less ) ;

cout << "After calling nth_element:\n" << endl ;

cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ;

} Program Output is: <pre class="fixed_text">Before calling nth_element:

Numbers { 4 10 70 30 10 69 96 100 }

After calling nth_element:

Numbers { 4 10 10 30 69 70 96 100 }

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