The sample code below illustrates how to use the predicate version of the random_shuffle
STL function in Visual C++.
Required Header:
<algorithm>
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 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 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).
//////////////////////////////////////////////////////////////////////
// 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 > 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:
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 }