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| 22 | <title>Identifiers (GNU C Language Manual)</title>
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| 58 | <span id="Identifiers"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Operators_002fPunctuation.html" accesskey="n" rel="next">Operators/Punctuation</a>, Previous: <a href="Comments.html" accesskey="p" rel="prev">Comments</a>, Up: <a href="Lexical-Syntax.html" accesskey="u" rel="up">Lexical Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="Identifiers-1"></span><h3 class="section">5.5 Identifiers</h3>
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| 64 | <span id="index-identifiers"></span>
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| 65 |
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| 66 | <p>An <em>identifier</em> (name) in C is a sequence of letters and digits,
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| 67 | as well as ‘<samp>_</samp>’, that does not start with a digit. Most compilers
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| 68 | also allow ‘<samp>$</samp>’. An identifier can be as long as you like; for
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| 69 | example,
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| 70 | </p>
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| 71 | <div class="example">
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| 72 | <pre class="example">int anti_dis_establishment_arian_ism;
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| 73 | </pre></div>
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| 74 |
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| 75 | <span id="index-case-of-letters-in-identifiers"></span>
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| 76 | <p>Letters in identifiers are case-sensitive in C; thus, <code>a</code>
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| 77 | and <code>A</code> are two different identifiers.
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| 78 | </p>
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| 79 | <span id="index-keyword"></span>
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| 80 | <span id="index-reserved-words"></span>
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| 81 | <p>Identifiers in C are used as variable names, function names, typedef
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| 82 | names, enumeration constants, type tags, field names, and labels.
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| 83 | Certain identifiers in C are <em>keywords</em>, which means they have
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| 84 | specific syntactic meanings. Keywords in C are <em>reserved words</em>,
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| 85 | meaning you cannot use them in any other way. For instance, you can’t
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| 86 | define a variable or function named <code>return</code> or <code>if</code>.
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| 87 | </p>
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| 88 | <p>You can also include other characters, even non-ASCII characters, in
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| 89 | identifiers by writing their Unicode character names, which start with
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| 90 | ‘<samp>\u</samp>’ or ‘<samp>\U</samp>’, in the identifier name. See <a href="Unicode-Character-Codes.html">Unicode Character Codes</a>. However, it is usually a bad idea to use non-ASCII
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| 91 | characters in identifiers, and when they are written in English, they
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| 92 | never need non-ASCII characters. See <a href="English.html">English</a>.
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| 93 | </p>
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| 94 | <p>Whitespace is required to separate two consecutive identifiers, or to
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| 95 | separate an identifier from a preceding or following numeric
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| 96 | constant.
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| 97 | </p>
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