Microsoft KB Archive/158000

= STL Sample for the nth_element Function =

Article ID: 158000

Article Last Modified on 12/10/2003

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APPLIES TO

 The Standard C++ Library, when used with:  Microsoft Visual C++ 4.2 Professional Edition

 Microsoft Visual C++ 4.2 Enterprise Edition

 Microsoft Visual C++ 5.0 Learning Edition 

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This article was previously published under Q158000

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SUMMARY
The sample code below illustrates how to use the nth_element STL function in Visual C++.

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Prototype
template<class RandomAccessIterator> inline void nth_element(RandomAccessIterator first,                   RandomAccessIterator nth,                    RandomAccessIterator last) 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 non-predicate version of nth_element uses operator< for comparisons.

Sample Code
////////////////////////////////////////////////////////////////////// // // Compile options needed: /GX // // nth_element.cpp : Illustrates how to use 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)

using namespace std;
 * 1) include
 * 2) include
 * 3) include
 * 4) include <BR/>

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) ;

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

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

Program Output is:

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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