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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
"../../../tools/boostbook/dtd/boostbook.dtd">
<!-- Copyright (c) 2001-2005 CrystalClear Software, Inc.
Subject to the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
-->
<section id="date_time.posix_time.time_iterators">
<title>Time Iterators</title>
<link linkend="time_iter_intro">Introduction</link> --
<link linkend="time_iter_header">Header</link> --
<link linkend="time_iter_overview">Overview</link> --
<link linkend="time_iter_operators">Operators</link>
<anchor id="time_iter_intro" />
<bridgehead renderas="sect3">Introduction</bridgehead>
<para>
Time iterators provide a mechanism for iteration through times. Time iterators are similar to <ulink url="http://www.sgi.com/tech/stl/BidirectionalIterator.html">Bidirectional Iterators</ulink>. However, time_iterators are different than standard iterators in that there is no underlying sequence, just a calculation function. In addition, time_iterators are directly comparable against instances of <link linkend="date_time.posix_time.ptime_class">class ptime</link>. Thus a second iterator for the end point of the iteration is not required, but rather a point in time can be used directly. For example, the following code iterates using a 15 minute iteration interval. The <link linkend="date_time.examples.print_hours">print hours</link> example also illustrates the use of the time_iterator.
</para>
<para>
<programlisting>
<![CDATA[
#include "boost/date_time/posix_time/posix_time.hpp"
#include <iostream>
int
main()
{
using namespace boost::gregorian;
using namespace boost::posix_time;
date d(2000,Jan,20);
ptime start(d);
ptime end = start + hours(1);
time_iterator titr(start,minutes(15)); //increment by 15 minutes
//produces 00:00:00, 00:15:00, 00:30:00, 00:45:00
while (titr < end) {
std::cout << to_simple_string(*titr) << std::endl;
++titr;
}
std::cout << "Now backward" << std::endl;
//produces 01:00:00, 00:45:00, 00:30:00, 00:15:00
while (titr > start) {
std::cout << to_simple_string(*titr) << std::endl;
--titr;
}
}
]]>
</programlisting>
</para>
<anchor id="time_iter_header" />
<bridgehead renderas="sect3">Header</bridgehead>
<para>
<programlisting>#include "boost/date_time/posix_time/posix_time.hpp" //include all types plus i/o
or
#include "boost/date_time/posix_time/posix_time_types.hpp" //no i/o just types</programlisting>
</para>
<anchor id="time_iter_overview" />
<bridgehead renderas="sect3">Overview</bridgehead>
<para>
<informaltable frame="all">
<tgroup cols="2">
<thead>
<row>
<entry valign="top" morerows="1">Class</entry>
<entry>Description</entry>
</row>
<row>
<entry>Construction Parameters</entry>
</row>
</thead>
<tbody>
<row>
<entry valign="top" morerows="1"><screen>time_iterator</screen></entry>
<entry>Iterate incrementing by the specified duration.</entry>
</row>
<row>
<entry><screen>ptime start_time, time_duration increment</screen></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<anchor id="time_iter_operators" />
<bridgehead renderas="sect3">Operators</bridgehead>
<para>
<informaltable frame="all">
<tgroup cols="2">
<thead>
<row>
<entry valign="top" morerows="1">Syntax</entry>
<entry>Description</entry>
</row>
<row>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry valign="top" morerows="1"><screen>operator==(const ptime& rhs),
operator!=(const ptime& rhs),
operator>, operator<,
operator>=, operator<=</screen>
</entry>
<entry>A full complement of comparison operators</entry>
</row>
<row>
<entry><screen>date d(2002,Jan,1);
ptime start_time(d, hours(1));
//increment by 10 minutes
time_iterator titr(start_time, minutes(10));
ptime end_time = start_time + hours(2);
if (titr == end_time) // false
if (titr != end_time) // true
if (titr >= end_time) // false
if (titr <= end_time) // true</screen>
</entry>
</row>
<row>
<entry valign="top" morerows="1"><screen>prefix increment</screen></entry>
<entry>Increment the iterator by the specified duration.</entry>
</row>
<row>
<entry><screen>//increment by 10 milli seconds
time_iterator titr(start_time, milliseconds(10));
++titr; // == start_time + 10 milliseconds</screen>
</entry>
</row>
<row>
<entry valign="top" morerows="1"><screen>prefix decrement</screen></entry>
<entry>Decrement the iterator by the specified time duration.</entry>
</row>
<row>
<entry><screen>time_duration td(1,2,3);
time_iterator titr(start_time, td);
--titr; // == start_time - 01:02:03</screen></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</section>
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