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<tr class="t-nv"><td colspan="5"> <a href="sizeof....html" title="cpp/language/sizeof...">sizeof...</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<p>Floating point literal defines a compile-time constant whose value is specified in the source file.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="floating_literal.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="floating_literal.html#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="floating_literal.html#Example"><span class="tocnumber">3</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="floating_literal.html#Notes"><span class="tocnumber">4</span> <span class="toctext">Notes</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/floating_literal&action=edit&section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
<p>Floating-point literals have two syntaxes. The first one consists of the following parts:
</p>
<dl><dd><ul><li> nonempty sequence of decimal digits containing a decimal point character (defines significand)
</li><li> <span class="t-mark">(optional)</span> <code><b>e</b></code> or <code><b>E</b></code> followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
</li><li> <span class="t-mark">(optional)</span> a suffix type specifier as a <code><b>l</b></code>, <code><b>f</b></code>, <code><b>L</b></code> or <code><b>F</b></code>
</li></ul>
</dd></dl>
<p>The second one consists of the following parts:
</p>
<dl><dd><ul><li> nonempty sequence of decimal digits (defines significant)
</li><li> <code><b>e</b></code> or <code><b>E</b></code> followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
</li><li> <span class="t-mark">(optional)</span> a suffix type specifier as a <code><b>l</b></code>, <code><b>f</b></code>, <code><b>L</b></code> or <code><b>F</b></code>
</li></ul>
</dd></dl>
<p>The suffix type specifier defines the actual type of the floating-point literal:
</p>
<dl><dd><ul><li> (no suffix) defines <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span>
</li><li> <code><b>f F</b></code> defines <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>
</li><li> <code><b>l L</b></code> defines <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span>
</li></ul>
</dd></dl>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx14"><td>Optional single quotes(<code>'</code>) can be inserted between the digits as a separator, they are ignored when compiling.</td>
<td><span class="t-mark-rev t-since-cxx14">(since C++14)</span></td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/floating_literal&action=edit&section=2" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span></h3>
<p>A decimal scientific notation is used, meaning that the exponent is the power of 10 by which the significant is multiplied.<br />
The mathematical meaning of <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu19">123e4</span></span></span> is <i>123×10<sup>4</sup></i>
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/floating_literal&action=edit&section=3" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include <iostream></span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="nu19">123.456e-67</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
<span class="sy1"><<</span> .1E4f <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
<span class="sy1"><<</span> <span class="nu0">58</span>. <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
<span class="sy1"><<</span> <span class="nu19">4e2</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">1.23456e-65
1000
58
400</pre></div></div>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/floating_literal&action=edit&section=4" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>The hexadecimal floating-point constants (e.g. <code>0x1p-5</code>, <code>0x1.0Ap-2</code>, <code>0x1.8p-1</code>), which are allowed in the C programming language, cannot be used as floating point literals in C++ (although some C++ compilers might interpret them). However, they may be parsed and printed by the I/O functions: both C++ I/O streams when <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/manip/fixed.html"><span class="kw1509">std::<span class="me2">hexfloat</span></span></a></span></span> is enabled and the C I/O streams: <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/c/printf.html"><span class="kw1568">std::<span class="me2">printf</span></span></a></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/c/scanf.html"><span class="kw1562">std::<span class="me2">scanf</span></span></a></span></span>, etc. See <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../string/byte/strtof.html"><span class="kw977">std::<span class="me2">strtof</span></span></a></span></span> for the format description
</p>
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