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Predicate Version of random_shuffle

Illustrates how to use the predicate version of the random_shuffle Standard Template Library (STL) function in Visual C++.

template<class RandomAccessIterator, class Predicate> inline 
   void random_shuffle( 
      RandomAccessIterator First, 
      RandomAccessIterator Last, 
      Predicate Pred 
   )
Note Note

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

The random_shuffle algorithm shuffles the elements of a sequence [First..Last) in a random order. The predicate version uses the Pred function to generate the indices of the elements to swap. The Pred has to be a function object that takes a parameter n and returns an integral random number in the range 0 - (n - 1). The predicate version of random_shuffle uses operator= to perform swaps.

// random_shufflePV.cpp
// compile with: /EHsc
// Illustrates how to use the predicate version
// of the random_shuffle function.
//
// Functions:
//    random_shuffle: Shuffle the elements in a random order.
//
//      Rand: Given n, generates an integral random number in the
//          in the range 0 - (n - 1).
//////////////////////////////////////////////////////////////////////

// disable warning C4786: symbol greater than 255 character,
// okay to ignore
#pragma warning(disable: 4786)
#define _CRT_RAND_S
#include <stdlib.h>
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>

using namespace std;

// return an integral random number in the range 0 - (n - 1)
int Rand(int n)
{
    unsigned int number;
    errno_t      err;

    err = rand_s(&number);
    if (err == 0)
      return number % n;
    else
      {
      printf_s("The rand_s function failed! Returning 0.\n");
      return 0;
      }
}

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] = 100;

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

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

   cout << "Before calling random_shuffle:" << endl;

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

   // shuffle the elements in a random order.
   // the pointer_to_unary_function adapter converts a function to a
   // function object.
   // Example output is listed, but the actual output is random.

   random_shuffle(start, end, pointer_to_unary_function<int, int>(Rand));

   cout << "After calling random_shuffle:" << endl;

   cout << "Numbers {";
   for (it = start; it != end; it++)
      cout << " " << *it;
   cout << " }" << endl;
}
Before calling random_shuffle:
Numbers { 4 10 70 30 10 69 96 100 }
After calling random_shuffle:
Numbers { 10 4 69 96 100 10 70 30 }

Header: <algorithm>

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