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  <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
  <meta name="dcterms.date" content="2022-03-11" />
  <title>Add @, \$, and \` to the basic character set</title>
  <style>
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      pre > code.sourceCode > span > a:first-child::before { text-decoration: underline; }
      }
      code span. { } /* Normal */
      code span.al { color: #ff0000; } /* Alert */
      code span.an { } /* Annotation */
      code span.at { } /* Attribute */
      code span.bn { color: #9f6807; } /* BaseN */
      code span.bu { color: #9f6807; } /* BuiltIn */
      code span.cf { color: #00607c; } /* ControlFlow */
      code span.ch { color: #9f6807; } /* Char */
      code span.cn { } /* Constant */
      code span.co { color: #008000; font-style: italic; } /* Comment */
      code span.cv { color: #008000; font-style: italic; } /* CommentVar */
      code span.do { color: #008000; } /* Documentation */
      code span.dt { color: #00607c; } /* DataType */
      code span.dv { color: #9f6807; } /* DecVal */
      code span.er { color: #ff0000; font-weight: bold; } /* Error */
      code span.ex { } /* Extension */
      code span.fl { color: #9f6807; } /* Float */
      code span.fu { } /* Function */
      code span.im { } /* Import */
      code span.in { color: #008000; } /* Information */
      code span.kw { color: #00607c; } /* Keyword */
      code span.op { color: #af1915; } /* Operator */
      code span.ot { } /* Other */
      code span.pp { color: #6f4e37; } /* Preprocessor */
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      code span.wa { color: #008000; font-weight: bold; } /* Warning */
      code.diff {color: #898887}
      code.diff span.va {color: #006e28}
      code.diff span.st {color: #bf0303}
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margin-top: -0.2em;
margin-bottom: -0.2em;
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opacity: .5;
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font-weight: normal;
font-size: 83%;
}
a.self-link:hover { opacity: 1; }
a.self-link::before { content: "§"; }
ul > li:before {
content: "\2014";
position: absolute;
margin-left: -1.5em;
}
:target { background-color: #C9FBC9; }
:target .codeblock { background-color: #C9FBC9; }
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a.marginalized {
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a.enumerated_item_num {
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a.index {
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a.index:before { content: "⟵"; }

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span.term { font-style: italic; }
span.terminal { font-family: monospace; font-style: normal; }
span.nonterminal { font-style: italic; }
span.tcode { font-family: monospace; font-style: normal; }
span.textbf { font-weight: bold; }
span.textsc { font-variant: small-caps; }
a.nontermdef { font-style: italic; font-family: serif; }
span.emph { font-style: italic; }
span.techterm { font-style: italic; }
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span.mathsf { font-family: sans-serif; }
span.mathrm { font-family: serif; font-style: normal; }
span.textrm { font-family: serif; }
span.textsl { font-style: italic; }
span.mathtt { font-family: monospace; font-style: normal; }
span.mbox { font-family: serif; font-style: normal; }
span.ungap { display: inline-block; width: 2pt; }
span.textit { font-style: italic; }
span.texttt { font-family: monospace; }
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<h1 class="title" style="text-align:center">Add @, $, and ` to the basic character set</h1>

<table style="border:none;float:right">
  <tr>
    <td>Document #:</td>
    <td>D2558R0</td>
  </tr>
  <tr>
    <td>Date:</td>
    <td>2022-03-11</td>
  </tr>
  <tr>
    <td style="vertical-align:top">Project:</td>
    <td>Programming Language C++</td>
  </tr>
  <tr>
    <td style="vertical-align:top">Audience:</td>
    <td>
      SG16<br>
      SG22<br>
      EWG<br>
    </td>
  </tr>
  <tr>
    <td style="vertical-align:top">Reply-to:</td>
    <td>
      Steve Downey<br>&lt;<a href="mailto:sdowney@gmail.com" class="email">sdowney@gmail.com</a>&gt;<br>
    </td>
  </tr>
</table>

</header>
<div style="clear:both">
<div id="TOC" role="doc-toc">
<h1 id="toctitle">Contents</h1>
<ul>
<li><a href="#abstract"><span class="toc-section-number">1</span> Abstract<span></span></a></li>
<li><a href="#motivation"><span class="toc-section-number">2</span> Motivation<span></span></a></li>
<li><a href="#wording"><span class="toc-section-number">3</span> Wording<span></span></a></li>
<li><a href="#bibliography"><span class="toc-section-number">4</span> References<span></span></a></li>
</ul>
</div>
<h1 data-number="1" id="abstract"><span class="header-section-number">1</span> Abstract<a href="#abstract" class="self-link"></a></h1>
<p>WG14, the C Standardization committee, is adopting <span class="citation" data-cites="CN2701">[<a href="#ref-CN2701" role="doc-biblioref">N2701</a>]</span> for C23. This will add U+0024 $ DOLLAR SIGN, U+0040 @ COMMERCIAL AT, and U+0060 ` GRAVE ACCENT to the basic source character set. C++ should adopt the same characters for C++26.</p>
<h1 data-number="2" id="motivation"><span class="header-section-number">2</span> Motivation<a href="#motivation" class="self-link"></a></h1>
<p>These characters are available in all encoded character sets in common use and everyone assumes that they are available, using them freely in source text. The primary change would be that these characters become available for syntactic purposes. Although using $ in identifiers is a common extension, they were not added to the identifier set in C, and this paper does not propose adding them either. Nor were trigraphs added in C for these characters, and this paper does not propose additional trigraphs or digraphs be added.</p>
<p>The translation model for C makes adding these to their basic source character set, the encoded set for source code before translation, much more compelling. These characters being already in the translation character set as single byte characters makes this less important for C++. Nonetheless, it would be useful to make these available for language purposes as the more conservative C language has agreed there are no functional impediments to their use.</p>
<p>Corentin Jabot discusses the usage in other programming languages extensively in <span class="citation" data-cites="P2342R0">[<a href="#ref-P2342R0" role="doc-biblioref">P2342R0</a>]</span>, <em>For a Few Punctuators More</em>, q.v.</p>
<h1 data-number="3" id="wording"><span class="header-section-number">3</span> Wording<a href="#wording" class="self-link"></a></h1>
<p>These changes are relative to <span class="citation" data-cites="N4901">[<a href="#ref-N4901" role="doc-biblioref">N4901</a>]</span> “Working Draft, Standard for Programming Language C++”</p>
<p>Modify [lex.charset] as follows:</p>
<p><span class="marginalizedparent"><a class="marginalized">2</a></span> The basic character set is a subset of the translation character set, consisting of <span class="rm" style="color: #bf0303"><del>96</del></span><span class="add" style="color: #006e28"><ins>99</ins></span> characters as specified in Table 1.</p>
<p>Modify [tab:lex.charset.basic] with the following additions:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb1-1"><a href="#cb1-1"></a>U+0009               CHARACTER TABULATION</span>
<span id="cb1-2"><a href="#cb1-2"></a>U+000B               LINE TABULATION</span>
<span id="cb1-3"><a href="#cb1-3"></a>U+000C               FORM FEED</span>
<span id="cb1-4"><a href="#cb1-4"></a>U+0020               SPACE</span>
<span id="cb1-5"><a href="#cb1-5"></a>U+000A               LINE FEED                    new-line</span>
<span id="cb1-6"><a href="#cb1-6"></a>U+0021               EXCLAMATION MARK             !</span>
<span id="cb1-7"><a href="#cb1-7"></a>U+0022               QUOTATION MARK               &quot;</span>
<span id="cb1-8"><a href="#cb1-8"></a>U+0023               NUMBER SIGN                  #</span></code></pre></div>
<div class="add" style="color: #006e28">

<div class="sourceCode" id="cb2"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb2-1"><a href="#cb2-1"></a>U+0024               DOLLAR SIGN                  $</span></code></pre></div>

</div>
<div class="sourceCode" id="cb3"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb3-1"><a href="#cb3-1"></a>U+0025               PERCENT SIGN                 %</span>
<span id="cb3-2"><a href="#cb3-2"></a>U+0026               AMPERSAND                    &amp;</span>
<span id="cb3-3"><a href="#cb3-3"></a>U+0027               APOSTROPHE                   &#39;</span>
<span id="cb3-4"><a href="#cb3-4"></a>U+0028               LEFT PARENTHESIS             (</span>
<span id="cb3-5"><a href="#cb3-5"></a>U+0029               RIGHT PARENTHESIS            )</span>
<span id="cb3-6"><a href="#cb3-6"></a>U+002A               ASTERISK                     *</span>
<span id="cb3-7"><a href="#cb3-7"></a>U+002B               PLUS SIGN                    +</span>
<span id="cb3-8"><a href="#cb3-8"></a>U+002C               COMMA                        ,</span>
<span id="cb3-9"><a href="#cb3-9"></a>U+002D               HYPHEN-MINUS                 -</span>
<span id="cb3-10"><a href="#cb3-10"></a>U+002E               FULL STOP                    .</span>
<span id="cb3-11"><a href="#cb3-11"></a>U+002F                SOLIDUS                     /</span>
<span id="cb3-12"><a href="#cb3-12"></a>U+0030 .. U+0039     DIGIT ZERO .. NINE           0 1 2 3 4 5 6 7 8 9</span>
<span id="cb3-13"><a href="#cb3-13"></a>U+003A               COLON  :</span>
<span id="cb3-14"><a href="#cb3-14"></a>U+003B               SEMICOLON                    ;</span>
<span id="cb3-15"><a href="#cb3-15"></a>U+003C               LESS-THAN SIGN               &lt;</span>
<span id="cb3-16"><a href="#cb3-16"></a>U+003D               EQUALS SIGN                  =</span>
<span id="cb3-17"><a href="#cb3-17"></a>U+003E               GREATER-THAN SIGN            &gt;</span>
<span id="cb3-18"><a href="#cb3-18"></a>U+003F               QUESTION MARK                ?</span></code></pre></div>
<div class="add" style="color: #006e28">

<div class="sourceCode" id="cb4"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb4-1"><a href="#cb4-1"></a>U+0040               COMMERCIAL AT                @</span></code></pre></div>

</div>
<div class="sourceCode" id="cb5"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb5-1"><a href="#cb5-1"></a>U+0041 .. U+005A     LATIN CAPITAL LETTER A .. Z  A B C D E F G H I J K L M</span>
<span id="cb5-2"><a href="#cb5-2"></a>                                                  N O P Q R S T U V W X Y Z</span>
<span id="cb5-3"><a href="#cb5-3"></a>U+005B               LEFT SQUARE BRACKET          [</span>
<span id="cb5-4"><a href="#cb5-4"></a>U+005C               REVERSE SOLIDUS              \</span>
<span id="cb5-5"><a href="#cb5-5"></a>U+005D               RIGHT SQUARE BRACKET         ]</span>
<span id="cb5-6"><a href="#cb5-6"></a>U+005E               CIRCUMFLEX ACCENT            ^</span>
<span id="cb5-7"><a href="#cb5-7"></a>U+005F               LOW LINE                     _</span></code></pre></div>
<div class="add" style="color: #006e28">

<div class="sourceCode" id="cb6"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb6-1"><a href="#cb6-1"></a>U+0060               GRAVE ACCENT                 `</span></code></pre></div>

</div>
<div class="sourceCode" id="cb7"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb7-1"><a href="#cb7-1"></a>U+0061 .. U+007A     LATIN SMALL LETTER A .. Z    a b c d e f g h i j k l m</span>
<span id="cb7-2"><a href="#cb7-2"></a>                                                  n o p q r s t u v w x y z</span>
<span id="cb7-3"><a href="#cb7-3"></a>U+007B               LEFT CURLY BRACKET           {</span>
<span id="cb7-4"><a href="#cb7-4"></a>U+007C               VERTICAL LINE                |</span>
<span id="cb7-5"><a href="#cb7-5"></a>U+007D               RIGHT CURLY BRACKET          }</span>
<span id="cb7-6"><a href="#cb7-6"></a>U+007E               TILDE                        ~</span></code></pre></div>
<h1 data-number="4" id="bibliography"><span class="header-section-number">4</span> References<a href="#bibliography" class="self-link"></a></h1>
<div id="refs" class="references hanging-indent" role="doc-bibliography">
<div id="ref-CN2701">
<p>[N2701] Philipp Klaus Krause. @ and $ in source and execution character set. <br />
<a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2701.htm">http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2701.htm</a></p>
</div>
<div id="ref-N4901">
<p>[N4901] Thomas Köppe. 2021-10-22. Working Draft, Standard for Programming Language C++. <br />
<a href="https://wg21.link/n4901">https://wg21.link/n4901</a></p>
</div>
<div id="ref-P2342R0">
<p>[P2342R0] Corentin Jabot. 2021-03-25. For a Few Punctuators More. <br />
<a href="https://wg21.link/p2342r0">https://wg21.link/p2342r0</a></p>
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