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90 lines
3.4 KiB
HTML
90 lines
3.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>log (LIBM)</title>
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<meta name="description" content="log (LIBM)">
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<meta name="keywords" content="log (LIBM)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Math.html#Math" rel="up" title="Math">
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<link href="log10.html#log10" rel="next" title="log10">
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<link href="ldexp.html#ldexp" rel="prev" title="ldexp">
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="log"></a>
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<div class="header">
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<p>
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Next: <a href="log10.html#log10" accesskey="n" rel="next">log10</a>, Previous: <a href="ldexp.html#ldexp" accesskey="p" rel="prev">ldexp</a>, Up: <a href="Math.html#Math" accesskey="u" rel="up">Math</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="log_002c-logf_002d_002d_002dnatural-logarithms"></a>
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<h3 class="section">1.34 <code>log</code>, <code>logf</code>—natural logarithms</h3>
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<a name="index-log"></a>
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<a name="index-logf"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <math.h>
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double log(double <var>x</var>);
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float logf(float <var>x</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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Return the natural logarithm of <var>x</var>, that is, its logarithm base e
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(where e is the base of the natural system of logarithms, 2.71828…).
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<code>log</code> and <code>logf</code> are identical save for the return and argument types.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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Normally, returns the calculated value. When <var>x</var> is zero, the
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returned value is <code>-HUGE_VAL</code> and <code>errno</code> is set to <code>ERANGE</code>.
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When <var>x</var> is negative, the returned value is NaN (not a number) and
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<code>errno</code> is set to <code>EDOM</code>.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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<code>log</code> is ANSI. <code>logf</code> is an extension.
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</p>
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<br>
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</body>
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</html>
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