Microsoft KB Archive/158004

= STL Sample for the random_shuffle Function =

Article ID: 158004

Article Last Modified on 6/23/2005

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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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This article was previously published under Q158004

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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> inline void random_shuffle(RandomAccessIterator first,                   RandomAccessIterator last) 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.

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. // // 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

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 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 }

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