algo/test_scan.cpp

This is an example of how to use stxxl::for_each() and stxxl::find() algorithms

/***************************************************************************
 * algo/test_scan.cpp
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2002 Roman Dementiev <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/


#include <iostream>
#include <algorithm>

#include <stxxl/vector>
#include <stxxl/scan>

using stxxl::int64;
using stxxl::timestamp;


template <typename type>
struct counter
{
 type value;
 counter(type v = type(0)) : value(v) { }
 type operator () ()
 {
 type old_val = value;
 value++;
 return old_val;
 }
};

template <typename type>
struct square
{
 void operator () (type & arg)
 {
 arg = arg * arg;
 }
};

template <typename type>
struct fill_value
{
 type val;
 fill_value(const type & v_) : val(v_) { }

 type operator () ()
 {
 return val;
 }
};

int main()
{
 stxxl::vector<int64>::size_type i;
 stxxl::vector<int64> v(64 * int64(1024 * 1024));
 double b, e;

 STXXL_MSG("write " << (v.end() - v.begin()) << " elements ...");

 stxxl::generate(v.begin(), v.end(), counter<int64>(), 4);


 STXXL_MSG("for_each_m ...");
 b = timestamp();
 stxxl::for_each_m(v.begin(), v.end(), square<int64>(), 4);
 e = timestamp();
 STXXL_MSG("for_each_m time: " << (e - b));


 STXXL_MSG("check");
 for (i = 0; i < v.size(); ++i)
 {
 if (v[i] != int64(i * i))
 STXXL_MSG("Error at position " << i);
 }

 STXXL_MSG("Pos of value 1023: " << (stxxl::find(v.begin(), v.end(), 1023, 4) - v.begin()));
 STXXL_MSG("Pos of value 1048576: " << (stxxl::find(v.begin(), v.end(), 1024 * 1024, 4) - v.begin()));
 STXXL_MSG("Pos of value 1024: " << (stxxl::find(v.begin(), v.end(), 32 * 32, 4) - v.begin()));

 STXXL_MSG("generate ...");
 b = timestamp();

 stxxl::generate(v.begin() + 1, v.end() - 1, fill_value<int64>(555), 4);
 e = timestamp();
 STXXL_MSG("generate: " << (e - b));


 STXXL_MSG("check");
 if (v[0] != 0)
 STXXL_MSG("Error at position " << i);
 if (v[v.size() - 1] != int64((v.size() - 1) * (v.size() - 1)))
 STXXL_MSG("Error at position " << i);

 for (i = 1; i < v.size() - 1; ++i)
 {
 if (v[i] != 555)
 STXXL_MSG("Error at position " << i);
 }

 return 0;
}