Use the random_shuffle STL function in Visual C++
This article describes how to use the random_shuffle
Standard Template Library (STL) function in Visual C++.
Original product version: Visual C++
Original KB number: 156994
Required header
<algorithm>
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 to (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).
// 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
#pragma warning(disable: 4786)
#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)
{
return rand() % n ;
}
void main()
{
const int VECTOR_SIZE = 8 ;
// Define a template class vector of int
typedef vector<int, allocator<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.
// 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:
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 }
References
For more information about the random_shuffle
function, visit random_shuffle (STL Samples).
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