Microsoft KB Archive/156994

= How to use the random_shuffle STL function in Visual C++ =

Article ID: 156994

Article Last Modified on 1/10/2006

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APPLIES TO

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

 Microsoft Visual C++ 5.0 Enterprise Edition

 Microsoft Visual C++ 6.0 Enterprise Edition

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul>

 Microsoft Visual C++ 2005 Express Edition</li></ul>

 Microsoft Visual C++ .NET 2003 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2002 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q156994

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Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code. Microsoft Visual C++ 2005 supports both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model.

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

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Prototype
template<class RandomAccessIterator, class Predicate> inline void random_shuffle(RandomAccessIterator first,                      RandomAccessIterator last,                       Predicate pred) 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 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.

Sample Code
////////////////////////////////////////////////////////////////////// // // Compile options needed: /GX // // random_shuffle.cpp: 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). // // 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

// return an integral random number in the range 0 - (n - 1) int Rand(int n) { return rand % n ; }

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 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. // the pointer_to_unary_function adapter converts a function to a   // function object. random_shuffle(start, end, pointer_to_unary_function<int, int>(Rand));

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

cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; } Program Output is: <pre class="fixed_text">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 }

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