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| 22 | <title>Character Constants (GNU C Language Manual)</title>
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Constants.html" rel="up" title="Constants">
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| 55 | </head>
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="Character-Constants"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="String-Constants.html" accesskey="n" rel="next">String Constants</a>, Previous: <a href="Invalid-Numbers.html" accesskey="p" rel="prev">Invalid Numbers</a>, Up: <a href="Constants.html" accesskey="u" rel="up">Constants</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="Character-Constants-1"></span><h3 class="section">12.6 Character Constants</h3>
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| 64 | <span id="index-character-constants"></span>
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| 65 | <span id="index-constants_002c-character"></span>
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| 66 | <span id="index-escape-sequence"></span>
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| 67 |
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| 68 | <p>A <em>character constant</em> is written with single quotes, as in
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| 69 | <code>'<var>c</var>'</code>. In the simplest case, <var>c</var> is a single ASCII
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| 70 | character that the constant should represent. The constant has type
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| 71 | <code>int</code>, and its value is the character code of that character.
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| 72 | For instance, <code>'a'</code> represents the character code for the letter
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| 73 | ‘<samp>a</samp>’: 97, that is.
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| 74 | </p>
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| 75 | <p>To put the ‘<samp>'</samp>’ character (single quote) in the character
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| 76 | constant, <em>quote</em> it with a backslash (‘<samp>\</samp>’). This character
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| 77 | constant looks like <code>'\''</code>. This sort of sequence, starting with
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| 78 | ‘<samp>\</samp>’, is called an <em>escape sequence</em>—the backslash character
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| 79 | here functions as a kind of <em>escape character</em>.
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| 80 | </p>
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| 81 | <p>To put the ‘<samp>\</samp>’ character (backslash) in the character constant,
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| 82 | quote it likewise with ‘<samp>\</samp>’ (another backslash). This character
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| 83 | constant looks like <code>'\\'</code>.
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| 84 | </p>
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| 85 | <span id="index-bell-character"></span>
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| 86 | <span id="index-_005ca"></span>
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| 87 | <span id="index-backspace"></span>
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| 88 | <span id="index-_005cb"></span>
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| 89 | <span id="index-tab-_0028ASCII-character_0029"></span>
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| 90 | <span id="index-_005ct"></span>
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| 91 | <span id="index-vertical-tab"></span>
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| 92 | <span id="index-_005cv"></span>
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| 93 | <span id="index-formfeed"></span>
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| 94 | <span id="index-_005cf"></span>
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| 95 | <span id="index-newline"></span>
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| 96 | <span id="index-_005cn"></span>
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| 97 | <span id="index-return-_0028ASCII-character_0029"></span>
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| 98 | <span id="index-_005cr"></span>
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| 99 | <span id="index-escape-_0028ASCII-character_0029"></span>
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| 100 | <span id="index-_005ce"></span>
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| 101 | <p>Here are all the escape sequences that represent specific
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| 102 | characters in a character constant. The numeric values shown are
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| 103 | the corresponding ASCII character codes, as decimal numbers.
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| 104 | </p>
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| 105 | <div class="example">
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| 106 | <pre class="example">'\a' ⇒ 7 /* <span class="roman">alarm, <kbd>CTRL-g</kbd></span> */
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| 107 | '\b' ⇒ 8 /* <span class="roman">backspace, <tt class="key">BS</tt>, <kbd>CTRL-h</kbd></span> */
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| 108 | '\t' ⇒ 9 /* <span class="roman">tab, <tt class="key">TAB</tt>, <kbd>CTRL-i</kbd></span> */
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| 109 | '\n' ⇒ 10 /* <span class="roman">newline, <kbd>CTRL-j</kbd></span> */
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| 110 | '\v' ⇒ 11 /* <span class="roman">vertical tab, <kbd>CTRL-k</kbd></span> */
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| 111 | '\f' ⇒ 12 /* <span class="roman">formfeed, <kbd>CTRL-l</kbd></span> */
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| 112 | '\r' ⇒ 13 /* <span class="roman">carriage return, <tt class="key">RET</tt>, <kbd>CTRL-m</kbd></span> */
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| 113 | '\e' ⇒ 27 /* <span class="roman">escape character, <tt class="key">ESC</tt>, <kbd>CTRL-[</kbd></span> */
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| 114 | '\\' ⇒ 92 /* <span class="roman">backslash character, <kbd>\</kbd></span> */
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| 115 | '\'' ⇒ 39 /* <span class="roman">singlequote character, <kbd>'</kbd></span> */
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| 116 | '\"' ⇒ 34 /* <span class="roman">doublequote character, <kbd>"</kbd></span> */
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| 117 | '\?' ⇒ 63 /* <span class="roman">question mark, <kbd>?</kbd></span> */
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| 118 | </pre></div>
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| 119 |
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| 120 | <p>‘<samp>\e</samp>’ is a GNU C extension; to stick to standard C, write ‘<samp>\33</samp>’.
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| 121 | </p>
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| 122 | <p>You can also write octal and hex character codes as
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| 123 | ‘<samp>\<var>octalcode</var></samp>’ or ‘<samp>\x<var>hexcode</var></samp>’. Decimal is not an
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| 124 | option here, so octal codes do not need to start with ‘<samp>0</samp>’.
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| 125 | </p>
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| 126 | <p>The character constant’s value has type <code>int</code>. However, the
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| 127 | character code is treated initially as a <code>char</code> value, which is
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| 128 | then converted to <code>int</code>. If the character code is greater than
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| 129 | 127 (<code>0177</code> in octal), the resulting <code>int</code> may be negative
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| 130 | on a platform where the type <code>char</code> is 8 bits long and signed.
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| 131 | </p>
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| 132 | <hr>
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| 133 | <div class="header">
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| 134 | <p>
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| 135 | Next: <a href="String-Constants.html" accesskey="n" rel="next">String Constants</a>, Previous: <a href="Invalid-Numbers.html" accesskey="p" rel="prev">Invalid Numbers</a>, Up: <a href="Constants.html" accesskey="u" rel="up">Constants</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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