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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>:
<a href="time.html">Date/time</a>: Datetime type</p>
<blockquote>
<pre class="lang">#include <ptime.h>
typedef large datetime;
datetime now(bool utc = true);
int days(datetime d);
int msecs(datetime d);
datetime mkdt(int days, int msecs);
bool isvalid(datetime d);
void tzupdate();
int tzoffset();
string dttostring(datetime d, const char* fmt);
string nowstring(const char* fmt, bool utc = true);
datetime utodatetime(time_t u);</pre>
</blockquote>
<p><span class="def">datetime now(bool utc = true)</span> returns the current
date/time. The returned value can be either the local time or the Universal Coordinated
Time (UTC, aka GMT), depending on the parameter <span class="lang">utc</span>.
It is recommended to manipulate with the UTC time internally in your application
whenever possible (f.ex. when it's not needed to display the time to the user),
since in many countries the local time may be automatically adjusted when entering
or leaving the daylight saving period, which may confuse your application. On
the contrary, the UTC time never changes. That's why all modern operating systems
rely on the UTC time internally. (See also <span class="lang">tzupdate()</span>
below for additional notes).</p>
<p><span class="def">int days(datetime d)</span> returns the number of days since
the beginning of the calendar contained in the <span class="lang">datetime</span>
value <span class="lang">d</span>.</p>
<p><span class="def">int msecs(datetime d)</span> returns the number of milliseconds
since midnight contained in the <span class="lang">datetime</span> value <span class="lang">d</span>.</p>
<p><span class="def">datetime mkdt(int days, int msecs)</span> calculates the
datetime value from <span class="lang">days</span> and <span class="lang">msecs</span>
parameters. <span class="lang">Days</span> is the number of days since the beginning
of the calendar, and <span class="lang">msecs</span> is the number of milliseconds
since midnight. No checks are made for validity of these values. There exists
an easier way to build a datetime value using <span class="lang">encodedate()</span>
and <span class="lang">encodetime()</span> functions having the year, month and
day numbers, as well as (not necessarily) the hour, minute, second and millisecond
values.</p>
<p><span class="def">bool isvalid(datetime d)</span> checks a <span class="lang">datetime</span>
value for validity. The value of <span class="lang">d</span> is valid if it holds
a time stamp between 01/01/0001 and 12/31/9999.</p>
<p><span class="def">void tzupdate()</span> updates the internal timezone information,
which affects the value of local time returned by <span class="lang">now()</span>
and <span class="lang">nowstring()</span>. If your application is supposed to
be running infinitely (e.g. if it's a network daemon), you might want to update
the internal timezone information from time to time in order to return correct
local time to the user on DST adjustment days. Depending on the precision of local
time you wish to show to the user, you can call this function, for example, every
minute or every hour. Without this, the local time may become incorrect at the
moment of DST adjustment, which occurs twice a year in most countries.</p>
<p><span class="def">int tzoffset()</span> returns the time zone offset in minutes.
This value is negative in the West. Multiplying this value by 60000 (i.e. the
offset in milliseconds) and adding it to the UTC <span class="lang">datetime</span>
value will give the local time.</p>
<p><span class="def">string dttostring(datetime d, const char* fmt)</span> converts
a <span class="lang">datetime</span> value to string representation as specified
by <span class="lang">fmt</span>. The syntax of the format specifier is the same
as for <span class="lang">strftime()</span> (please, refer to the corresponding
manual pages in your programming environment). Note that there might be slight
incompatibilities between different implementations of <span class="lang">strftime()</span>.
</p>
<p><span class="def">string nowstring(const char* fmt, bool utc = true)</span>
returns a string representing the current time in a format specified by <span class="lang">fmt</span>.
<span class="lang">Utc</span> specifies whether the local time or the UTC time
is required. Like for <span class="lang">dttostring()</span>, the syntax of the
format specifier <span class="lang">fmt</span> is the same as for the system function
<span class="lang">strftime()</span>.</p>
<p><span class="def">datetime utodatetime(time_t u)</span> converts UNIX <span class="lang">time_t</span>
value to PTypes <span class="lang">datetime</span>.</p>
<p class="seealso">See also: <a href="time.calendar.html">Date/calendar manipulation</a>,
<a href="time.time.html">Time manipulation</a></p>
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