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examples/algo/phonebills.cpp

This example code is explain in A Billing System for Phone Calls (stxxl::vector and stxxl::sort)

/***************************************************************************
* examples/algo/phonebills.cpp
*
* Part of the STXXL. See http://stxxl.sourceforge.net
*
* Copyright (C) 2004 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)
**************************************************************************/
#define USE_STXXL
//! [prolog]
#include <stxxl.h> // STXXL header
#include <algorithm> // for STL std::sort
#include <vector> // for STL std::vector
#include <fstream> // for std::fstream
#include <ctime> // for time_t type
#define CT_PER_MIN 2 // subscribers pay 2 cent per minute
struct LogEntry // the event log data structure
{
long long int from; // callers number (64 bit integer)
long long int to; // destination number (64 bit int)
time_t timestamp; // time of event
int event; // event type 1 - call started
// 2 - call ended
};
// input operator used for reading from the file
std::istream& operator >> (std::istream& i, LogEntry& entry)
{
i >> entry.from;
i >> entry.to;
i >> entry.timestamp;
i >> entry.event;
return i;
}
// output operator used for writing to file
std::ostream& operator << (std::ostream& i, const LogEntry& entry)
{
i << entry.from << " ";
i << entry.to << " ";
i << entry.timestamp << " ";
i << entry.event;
return i;
}
// unary function used for producing the bills
struct ProduceBill
{
std::ostream& out; // stream for outputting
// the bills
unsigned sum; // current subscribers debit
LogEntry last; // the last record
ProduceBill(std::ostream& o_) : out(o_), sum(0) { last.from = -1; }
void operator () (const LogEntry& e)
{
if (last.from == e.from)
{
// either the last event was 'call started' and current event
// is 'call ended' or the last event was 'call ended' and
// current event is 'call started'
assert((last.event == 1 && e.event == 2) ||
(last.event == 2 && e.event == 1));
if (e.event == 2) // call ended
sum += CT_PER_MIN * (unsigned int)(e.timestamp - last.timestamp) / 60;
}
else if (last.from != -1)
{
assert(last.event == 2); // must be 'call ended'
assert(e.event == 1); // must be 'call started'
// output the total sum
out << last.from << "; " << (sum / 100) << " EUR " << (sum % 100) <<
" ct" << std::endl;
sum = 0; // reset the sum
}
last = e;
}
};
struct SortByCaller
{
// comparison function
bool operator () (const LogEntry& a, const LogEntry& b) const
{
return a.from < b.from ||
(a.from == b.from && a.timestamp < b.timestamp) ||
(a.from == b.from && a.timestamp == b.timestamp &&
a.event < b.event);
}
// min sentinel = value which is strictly smaller that any input element
static LogEntry min_value()
{
LogEntry dummy;
dummy.timestamp = std::numeric_limits<time_t>::min();
return dummy;
}
// max sentinel = value which is strictly larger that any input element
static LogEntry max_value()
{
LogEntry dummy;
dummy.timestamp = std::numeric_limits<time_t>::max();
return dummy;
}
};
void print_usage(const char* program)
{
std::cout << "Usage: " << program << " logfile main billfile" << std::endl;
std::cout << " logfile - file name of the input" << std::endl;
std::cout << " main - memory to use (in MiB)" << std::endl;
std::cout << " billfile - file name of the output" << std::endl;
}
//! [prolog]
#ifdef USE_STXXL
typedef stxxl::vector<LogEntry> vector_type;
#else
typedef std::vector<LogEntry> vector_type;
#endif
int main(int argc, char* argv[])
{
if (argc < 4)
{
print_usage(argv[0]);
return 0;
}
// read from the file
std::fstream in(argv[1], std::ios::in);
vector_type v;
std::copy(std::istream_iterator<LogEntry>(in),
std::istream_iterator<LogEntry>(),
std::back_inserter(v));
// sort by callers
#ifndef USE_STXXL
std::sort(v.begin(), v.end(), SortByCaller());
std::fstream out(argv[3], std::ios::out);
// output bills
std::for_each(v.begin(), v.end(), ProduceBill(out));
#else
const unsigned M = atol(argv[2]) * 1024 * 1024;
stxxl::sort(v.begin(), v.end(), SortByCaller(), M);
std::fstream out(argv[3], std::ios::out);
// output bills
stxxl::for_each(v.begin(), v.end(), ProduceBill(out), M / vector_type::block_type::raw_size);
#endif
return 0;
}
//! [example]