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<p>Comments serve as a sort of in-code documentation. When inserted into a program, they are effectively ignored by the compiler; they are solely intended to be used as notes by the humans that read source code. Although specific documentation is not part of the C++ standard, several utilities exist that parse comments with different documentation formats.
</p>
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<li class="toclevel-1 tocsection-1"><a href="comments.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="comments.html#C-style"><span class="tocnumber">2</span> <span class="toctext">C-style</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="comments.html#C.2B.2B-style"><span class="tocnumber">3</span> <span class="toctext">C++-style</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="comments.html#Notes"><span class="tocnumber">4</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="comments.html#Example"><span class="tocnumber">5</span> <span class="toctext">Example</span></a></li>
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<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
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<td> <code><b>/*</b></code> <span class="t-spar">comment</span> <code><b>*/</b></code>
</td>
<td> (1)
</td>
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</td></tr>
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<td> <code><b>//</b></code> <span class="t-spar">comment</span>\n
</td>
<td> (2)
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<div class="t-li1"><span class="t-li">1)</span> Often known as "C-style" or "multi-line" comments.</div>
<div class="t-li1"><span class="t-li">2)</span> Often known as "C++-style" or "single-line" comments.</div>
<p>All comments are removed from the program at <a href="language/translation_phases.html" title="cpp/language/translation phases">translation phase 3</a> by replacing each comment with a single whitespace character.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=2" title="Edit section: C-style">edit</a>]</span> <span class="mw-headline" id="C-style">C-style</span></h3>
<p>C-style comments are usually used to comment large blocks of text, however, they can be used to comment single lines. To insert a C-style comment, simply surround text with <code>/*</code> and <code>*/</code>; this will cause the contents of the comment to be ignored by the compiler. Although it is not part of the C++ standard, <code>/**</code> and <code>*/</code> are often used to indicate documentation blocks; this is legal because the second asterisk is simply treated as part of the comment. C-style comments cannot be nested.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=3" title="Edit section: C++-style">edit</a>]</span> <span class="mw-headline" id="C.2B.2B-style">C++-style</span></h3>
<p>C++-style comments are usually used to comment single lines, however, multiple C++-style comments can be placed together to form multi-line comments. C++-style comments tell the compiler to ignore all content between <code>//</code> and a new line.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=4" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>Because comments <a href="language/translation_phases.html" title="cpp/language/translation phases">are removed</a> before the preprocessor stage, a macro cannot be used to form a comment and an unterminated C-style comment doesn't spill over from an #include'd file.
</p><p>Besides commenting out, other mechanisms used for source code exclusion are
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#if 0</span>
<a href="io/cout.html"><span class="kw1552">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"this will not be executed or even compiled<span class="es1">\n</span>"</span><span class="sy4">;</span>
<span class="co2">#endif</span></pre></div></div>
<p>and
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">if</span><span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span> <span class="br0">{</span>
<a href="io/cout.html"><span class="kw1552">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"this will not be executed<span class="es1">\n</span>"</span>
<span class="br0">}</span></pre></div></div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=5" 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="coMULTI">/* C-style comments can contain
multiple lines */</span>
<span class="coMULTI">/* or just one */</span>
 
<span class="co1">// C++-style comments can comment one line</span>
 
<span class="co1">// or, they can</span>
<span class="co1">// be strung together</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co1">// The below code won't be run</span>
<span class="co1">// return 1;</span>
 
<span class="co1">// The below code will be run</span>
<span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p><br />
</p>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/comment&action=edit&section=6" title="Edit section: See Also">edit</a>]</span> <span class="mw-headline" id="See_Also">See Also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../c/comment.html" title="c/comment">C documentation</a></span> for <span class="t-dsc-see-tt"><span>comment</span></span></div>
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