<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
<html>
|
<!-- Copyright (C) 1999-2016 Free Software Foundation, Inc.
|
|
Permission is granted to copy, distribute and/or modify this document
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
any later version published by the Free Software Foundation; with the
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
(see below). A copy of the license is included in the section entitled
|
"GNU Free Documentation License".
|
|
(a) The FSF's Front-Cover Text is:
|
|
A GNU Manual
|
|
(b) The FSF's Back-Cover Text is:
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
software. Copies published by the Free Software Foundation raise
|
funds for GNU development. -->
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
<head>
|
<title>The GNU Fortran Compiler: SYSTEM_CLOCK</title>
|
|
<meta name="description" content="The GNU Fortran Compiler: SYSTEM_CLOCK">
|
<meta name="keywords" content="The GNU Fortran Compiler: SYSTEM_CLOCK">
|
<meta name="resource-type" content="document">
|
<meta name="distribution" content="global">
|
<meta name="Generator" content="makeinfo">
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
<link href="index.html#Top" rel="start" title="Top">
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
<link href="Intrinsic-Procedures.html#Intrinsic-Procedures" rel="up" title="Intrinsic Procedures">
|
<link href="TAN.html#TAN" rel="next" title="TAN">
|
<link href="SYSTEM.html#SYSTEM" rel="prev" title="SYSTEM">
|
<style type="text/css">
|
<!--
|
a.summary-letter {text-decoration: none}
|
blockquote.smallquotation {font-size: smaller}
|
div.display {margin-left: 3.2em}
|
div.example {margin-left: 3.2em}
|
div.indentedblock {margin-left: 3.2em}
|
div.lisp {margin-left: 3.2em}
|
div.smalldisplay {margin-left: 3.2em}
|
div.smallexample {margin-left: 3.2em}
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
div.smalllisp {margin-left: 3.2em}
|
kbd {font-style:oblique}
|
pre.display {font-family: inherit}
|
pre.format {font-family: inherit}
|
pre.menu-comment {font-family: serif}
|
pre.menu-preformatted {font-family: serif}
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
pre.smallexample {font-size: smaller}
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
pre.smalllisp {font-size: smaller}
|
span.nocodebreak {white-space:nowrap}
|
span.nolinebreak {white-space:nowrap}
|
span.roman {font-family:serif; font-weight:normal}
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
ul.no-bullet {list-style: none}
|
-->
|
</style>
|
|
|
</head>
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
<a name="SYSTEM_005fCLOCK"></a>
|
<div class="header">
|
<p>
|
Next: <a href="TAN.html#TAN" accesskey="n" rel="next">TAN</a>, Previous: <a href="SYSTEM.html#SYSTEM" accesskey="p" rel="prev">SYSTEM</a>, Up: <a href="Intrinsic-Procedures.html#Intrinsic-Procedures" accesskey="u" rel="up">Intrinsic Procedures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
<hr>
|
<a name="SYSTEM_005fCLOCK-_002d_002d_002d-Time-function"></a>
|
<h3 class="section">9.254 <code>SYSTEM_CLOCK</code> — Time function</h3>
|
<a name="index-SYSTEM_005fCLOCK"></a>
|
<a name="index-time_002c-clock-ticks-2"></a>
|
<a name="index-clock-ticks-2"></a>
|
|
<dl compact="compact">
|
<dt><em>Description</em>:</dt>
|
<dd><p>Determines the <var>COUNT</var> of a processor clock since an unspecified
|
time in the past modulo <var>COUNT_MAX</var>, <var>COUNT_RATE</var> determines
|
the number of clock ticks per second. If the platform supports a
|
monotonic clock, that clock is used and can, depending on the platform
|
clock implementation, provide up to nanosecond resolution. If a
|
monotonic clock is not available, the implementation falls back to a
|
realtime clock.
|
</p>
|
<p><var>COUNT_RATE</var> is system dependent and can vary depending on the kind of
|
the arguments. For <var>kind=4</var> arguments (and smaller integer kinds),
|
<var>COUNT</var> represents milliseconds, while for <var>kind=8</var> arguments (and
|
larger integer kinds), <var>COUNT</var> typically represents micro- or
|
nanoseconds depending on resolution of the underlying platform clock.
|
<var>COUNT_MAX</var> usually equals <code>HUGE(COUNT_MAX)</code>. Note that the
|
millisecond resolution of the <var>kind=4</var> version implies that the
|
<var>COUNT</var> will wrap around in roughly 25 days. In order to avoid issues
|
with the wrap around and for more precise timing, please use the
|
<var>kind=8</var> version.
|
</p>
|
<p>If there is no clock, or querying the clock fails, <var>COUNT</var> is set
|
to <code>-HUGE(COUNT)</code>, and <var>COUNT_RATE</var> and <var>COUNT_MAX</var> are
|
set to zero.
|
</p>
|
<p>When running on a platform using the GNU C library (glibc) version
|
2.16 or older, or a derivative thereof, the high resolution monotonic
|
clock is available only when linking with the <var>rt</var> library. This
|
can be done explicitly by adding the <code>-lrt</code> flag when linking the
|
application, but is also done implicitly when using OpenMP.
|
</p>
|
<p>On the Windows platform, the version with <var>kind=4</var> arguments uses
|
the <code>GetTickCount</code> function, whereas the <var>kind=8</var> version
|
uses <code>QueryPerformanceCounter</code> and
|
<code>QueryPerformanceCounterFrequency</code>. For more information, and
|
potential caveats, please see the platform documentation.
|
</p>
|
</dd>
|
<dt><em>Standard</em>:</dt>
|
<dd><p>Fortran 95 and later
|
</p>
|
</dd>
|
<dt><em>Class</em>:</dt>
|
<dd><p>Subroutine
|
</p>
|
</dd>
|
<dt><em>Syntax</em>:</dt>
|
<dd><p><code>CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])</code>
|
</p>
|
</dd>
|
<dt><em>Arguments</em>:</dt>
|
<dd><table>
|
<tr><td width="15%"><var>COUNT</var></td><td width="70%">(Optional) shall be a scalar of type
|
<code>INTEGER</code> with <code>INTENT(OUT)</code>.</td></tr>
|
<tr><td width="15%"><var>COUNT_RATE</var></td><td width="70%">(Optional) shall be a scalar of type
|
<code>INTEGER</code> or <code>REAL</code>, with <code>INTENT(OUT)</code>.</td></tr>
|
<tr><td width="15%"><var>COUNT_MAX</var></td><td width="70%">(Optional) shall be a scalar of type
|
<code>INTEGER</code> with <code>INTENT(OUT)</code>.</td></tr>
|
</table>
|
|
</dd>
|
<dt><em>Example</em>:</dt>
|
<dd><div class="smallexample">
|
<pre class="smallexample">PROGRAM test_system_clock
|
INTEGER :: count, count_rate, count_max
|
CALL SYSTEM_CLOCK(count, count_rate, count_max)
|
WRITE(*,*) count, count_rate, count_max
|
END PROGRAM
|
</pre></div>
|
|
</dd>
|
<dt><em>See also</em>:</dt>
|
<dd><p><a href="DATE_005fAND_005fTIME.html#DATE_005fAND_005fTIME">DATE_AND_TIME</a>, <a href="CPU_005fTIME.html#CPU_005fTIME">CPU_TIME</a>
|
</p></dd>
|
</dl>
|
|
|
|
<hr>
|
<div class="header">
|
<p>
|
Next: <a href="TAN.html#TAN" accesskey="n" rel="next">TAN</a>, Previous: <a href="SYSTEM.html#SYSTEM" accesskey="p" rel="prev">SYSTEM</a>, Up: <a href="Intrinsic-Procedures.html#Intrinsic-Procedures" accesskey="u" rel="up">Intrinsic Procedures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
|
|
|
</body>
|
</html>
|
