random_shuffle (STL Sample)

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

Required Header:
<algorithm>

template<class RandomAccessIterator> inline
     void random_shuffle(RandomAccessIterator first,
     RandomAccessIterator last)

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

Description:
The random_shuffle algorithm shuffles the elements of a sequence [first..last) in a random order. The non-predicate version uses an internal random-number generator to generate the indices of the elements to swap. The non-predicate version of random_shuffle uses operator= to perform swaps.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// random_shuffle.cpp : Illustrates how to use the random_shuffle
//                      function.
//
// Functions:
//
//     random_shuffle : Shuffle the elements in a random order.
//////////////////////////////////////////////////////////////////////

// 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> 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 random_shuffle\n" << endl ;

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

    // shuffle the elements in a random order
    random_shuffle(start, end) ;

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

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

 

Program Output is:

Before calling random_shuffle

Numbers { 4 10 70 30 10 69 96 100  }

After calling random_shuffle

Numbers { 10 30 4 70 96 100 69 10  }