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partial_sort (STL Samples) 

Illustrates how to use the partial_sort Standard Template Library (STL) function in Visual C++.


template<class RandomAccessIterator> inline
   void partial_sort(
      RandomAccessIterator First,
      RandomAccessIterator Middle,
      RandomAccessIterator Last
   )
NoteNote

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The partial_sort algorithm sorts the smallest n elements, where n = Middle - First of the sequence [First, Last). The remaining elements end up in the range [Middle..Last) in an undefined order. The nonpredicate version of partial_sort uses operator< for comparisons.

// partial_sort.cpp
// compile with: /EHsc
// Illustrates how to use the partial_sort function.
//
// Functions:
//    partial_sort : Sort the smallest N elements in a sequence.

// 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 ;

int main()
{
    const int VECTOR_SIZE = 8 ;

    // Define a template class vector of int
    typedef vector<int> 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] = 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\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 sequence
    partial_sort(start, start+4, end) ;

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

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

Numbers { 4 10 70 30 10 69 96 7  }

After calling partial_sort

Numbers { 4 7 10 10 70 69 96 30  }

Header: <algorithm>

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