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STL Sample for the partial_sort_copy Function

Retired KB ArticleThis article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
Article ID:158003
Last Review:December 8, 2003
Revision:2.0
This article was previously published under Q158003
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SUMMARY

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

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MORE INFORMATION

Required Header

   <algorithm>
				

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Prototype

   template<class InputIterator, RandomAccessIterator> inline
   RandomAccessIterator partial_sort(InputIterator first1,
                                     InputIterator last1,
                                     RandomAccessIterator first2,
                                     RandomAccessIterator last2)
				
NOTE: The class/parameter names in the prototype do not match the original version in the header file. Some have been modified to improve readability.

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Description

The partial_sort_copy algorithm sorts the smallest N elements, where N = min((last1 - first1), (last2 - first2)), of the sequence [first1, last1) and copies the results to the sequence [first2, first2 + N].

The non-predicate version of partial_sort_copy uses operator< for comparisons.

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Sample Code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// partial_sort_copy.cpp : Illustrates how to use the partial_sort_copy
//                         function.
// 
// Functions:
// 
//    partial_sort_copy : Sort the smallest N elements in a sequence
//                        and copy the resulting sequence
//                        to another sequence.
// 
// 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
#pragma warning(disable: 4786)

#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;

void main()
{
    const int VECTOR_SIZE = 8 ;

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

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

    IntVector Numbers(VECTOR_SIZE) ;
    IntVector Result(4) ;

    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] = 7;

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

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

    cout << "Before calling partial_sort_copy\n" << endl ;

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

    // sort the smallest 4 elements in the Numbers
    // and copy the results in Result
    partial_sort_copy(start, end, Result.begin(), Result.end()) ;

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

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

    cout << "Result { " ;
    for(it = Result.begin(); it != Result.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;
}

Program Output  is:

Before calling partial_sort_copy

Numbers { 4 10 70 30 10 69 96 7  }

After calling partial_sort_copy

Numbers { 4 10 70 30 10 69 96 7  }

Result { 4 7 10 10  }
				

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REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

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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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Keywords: 
kbcode kbhowto KB158003

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