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Introduce julian.h

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Howard Hinnant
2016-06-26 18:49:51 -04:00
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>julian</title>
<style>
p {text-align:justify}
li {text-align:justify}
blockquote.note
{
background-color:#E0E0E0;
padding-left: 15px;
padding-right: 15px;
padding-top: 1px;
padding-bottom: 1px;
}
ins {color:#00A000}
del {color:#A00000}
code {white-space:pre;}
</style>
</head>
<body>
<address align=right>
<br/>
<br/>
<a href="mailto:howard.hinnant@gmail.com">Howard E. Hinnant</a><br/>
2016-06-26<br/>
</address>
<hr/>
<h1 align=center><code>julian</code></h1>
<h2>Contents</h2>
<ul>
<li><a href="https://github.com/HowardHinnant/date">github link</a></li>
<li><a href="#Introduction">Introduction</a></li>
</ul>
<a name="Introduction"></a><h2>Introduction</h2>
<p>
This is a Julian calendar in the style of
<a href="date.html">date.h</a>.
Everthing is the same here as for
<a href="date.html">date.h</a>,
except that the calendrical arithmetic implements a proleptic Julian calendar.
</p>
<p>
The <code>julian</code> calendar can interoperate with
<a href="date.html">date.h</a> and <a href="tz.html">tz.h</a> just by
paying attention to the namespace. For example to convert the <i>civil</i>
date <code>2016_y/jun/26</code> to a julian date, just do:
</p>
<blockquote><pre>
#include "julian.h"
#include &lt;iostream&gt;
int
main()
{
using namespace date::literals;
std::cout &lt;&lt; julian::year_month_day{2016_y/jun/26} &lt;&lt; '\n';
}
</pre></blockquote>
<p>
This outputs:
</p>
<blockquote><pre>
2016-06-13
</pre></blockquote>
<p>
And here is the reverse conversion:
</p>
<blockquote><pre>
#include "julian.h"
#include &lt;iostream&gt;
int
main()
{
using namespace julian::literals;
std::cout &lt;&lt; date::year_month_day{2016_y/jun/13} &lt;&lt; '\n';
}
</pre></blockquote>
<p>
Which outputs:
</p>
<blockquote><pre>
2016-06-26
</pre></blockquote>
<p>
You can even convert directly to the ISO-week-based calendar:
</p>
<blockquote><pre>
#include "iso_week.h"
#include "julian.h"
#include &lt;iostream&gt;
int
main()
{
using namespace julian::literals;
std::cout &lt;&lt; iso_week::year_weeknum_weekday{2016_y/jun/13} &lt;&lt; '\n';
}
</pre></blockquote>
<p>
Which outputs:
</p>
<blockquote><pre>
2016-W25-Sun
</pre></blockquote>
<p>
<p>
You can find the current local julian date and time with:
</p>
<blockquote><pre>
#include "julian.h"
#include "tz.h"
#include &lt;iostream&gt;
int
main()
{
auto zt = date::make_zoned(date::current_zone(), std::chrono::system_clock::now());
auto ld = date::floor&lt;date::days&gt;(zt.get_local_time());
julian::year_month_day ymd{ld};
auto time = date::make_time(zt.get_local_time() - ld);
std::cout &lt;&lt; ymd &lt;&lt; ' ' &lt;&lt; time &lt;&lt; '\n';
}
</pre></blockquote>
<p>
Example output:
</p>
<blockquote><pre>
2016-06-13 18:38:30.049598
</pre></blockquote>
</body>
</html>