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Ref-docs/c_lib_guide/1.1.html
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Ref-docs/c_lib_guide/1.1.html
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<html>
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<head>
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<title>
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C Guide--1.1 Characters
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</title>
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<!-- Changed by: eric huss, 12-Mar-1997 -->
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</head>
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<body text="#000000" bgcolor="#FFFFFF">
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<center>
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<table border=0 width=100%>
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<tr>
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<td align=left width=20% valign=top>
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<a href="index.html">
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<img src="left.gif" border=0>
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Previous Section<br>
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TOC</a></td>
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<td align=center width=60% valign=top>
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| <a href="index.html">Table of Contents</a> |
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<a href="index2.html">Index</a> |</td>
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<td align=right width=20% valign=top>
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<a href="1.2.html">
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Next Section
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<img src="right.gif" border=0><br>
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1.2 Identifiers</a></td>
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</tr>
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</table>
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</center>
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<hr>
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<p>
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<h1>1.1.1 Trigraph Characters</h1>
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<p>
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A trigraph sequence found in the source code is converted to its respective translation
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character. This allows people to enter certain characters that are not allowed under some (rare)
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platforms.
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<center>
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<table>
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<tr ALIGN=CENTER>
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<td>Trigraph Sequence</td>
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<td>Translation Character</td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??=</b></code></td>
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<td><code><b>#</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??(</b></code></td>
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<td><code><b>[</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??/</b></code></td>
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<td><code><b>\</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??)</b></code></td>
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<td><code><b>]</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??'</b></code></td>
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<td><code><b>^</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??<</b></code></td>
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<td><code><b>{</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??!</b></code></td>
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<td><code><b>|</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??></b></code></td>
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<td><code><b>}</b></code></td>
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</tr>
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<tr ALIGN=CENTER>
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<td><code><b>??-</b></code></td>
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<td><code><b>~</b></code></td>
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</tr>
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</table>
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</center>
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Example:
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<blockquote><code><b>
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printf("No???/n");
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</b></code></blockquote>
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translates into:
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<blockquote><code><b>
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printf("No?\n");
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</b></code></blockquote>
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<h1>1.1.2 Escape sequences</h1>
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<p>
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The following escape sequences allow special characters to be put
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into the source code.
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<center>
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<table>
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<tr>
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<td>Escape Sequence</td>
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<td>Name</td>
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<td>Meaning</td>
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</tr>
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<tr>
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<td><code><b>\a</b></code></td>
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<td>Alert</td>
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<td>Produces an audible or visible alert.</td>
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</tr>
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<tr>
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<td><code><b>\b</b></code></td>
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<td>Backspace</td>
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<td>Moves the cursor back one position (non-destructive).</td>
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</tr>
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<tr>
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<td><code><b>\f</b></code></td>
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<td>Form Feed</td>
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<td>Moves the cursor to the first position of the next page.</td>
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</tr>
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<tr>
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<td><code><b>\n</b></code></td>
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<td>New Line</td>
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<td>Moves the cursor to the first position of the next line.</td>
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</tr>
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<tr>
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<td><code><b>\r</b></code></td>
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<td>Carriage Return</td>
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<td>Moves the cursor to the first position of the current line.</td>
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</tr>
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<tr>
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<td><code><b>\t</b></code></td>
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<td>Horizontal Tab</td>
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<td>Moves the cursor to the next horizontal tabular position.</td>
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</tr>
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<tr>
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<td><code><b>\v</b></code></td>
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<td>Vertical Tab</td>
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<td>Moves the cursor to the next vertical tabular position.</td>
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</tr>
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<tr>
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<td><code><b>\'</b></code></td>
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<td></td>
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<td>Produces a single quote.</td>
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</tr>
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<tr>
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<td><code><b>\"</b></code></td>
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<td></td>
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<td>Produces a double quote.</td>
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</tr>
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<tr>
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<td><code><b>\?</b></code></td>
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<td></td>
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<td>Produces a question mark.</td>
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</tr>
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<tr>
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<td><code><b>\\</b></code></td>
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<td></td>
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<td>Produces a single backslash.</td>
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</tr>
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<tr>
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<td><code><b>\0</b></code></td>
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<td></td>
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<td>Produces a null character.</td>
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</tr>
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<tr>
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<td><code><b>\</b></code><i>ddd</i></td>
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<td></td>
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<td>Defines one character by the octal digits (base-8 number).
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Multiple characters may be defined in the same escape
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sequence, but the value is implementation-specific (see examples).
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</td>
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</tr>
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<tr>
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<td><code><b>\x</b></code><i>dd</i></td>
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<td></td>
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<td>Defines one character by the hexadecimal digit (base-16 number).</td>
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</tr>
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</table>
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</center>
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Examples:
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<blockquote>
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<code><b>printf("\12");</b></code><br>
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Produces the decimal character 10 (x0A Hex).<br>
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<br>
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<code><b>printf("\xFF");</b></code><br>
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Produces the decimal character -1 or 255 (depending on sign).<br>
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<br>
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<code><b>printf("\x123");</b></code><br>
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Produces a single character (value is undefined). May cause errors.<br>
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<br>
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<code><b>printf("\0222");</b></code><br>
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Produces two characters whose values are implementation-specific.
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</blockquote>
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<h1>1.1.3 Comments</h1>
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<p>
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Comments in the source code are ignored by the compiler. They are encapsulated
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starting with <code><b>/*</b></code> and ending with
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<code><b>*/</b></code>. According to the ANSI standard,
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nested comments are not allowed, although some implementations allow it.
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<p>
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Single line comments are becoming more common, although not defined in the ANSI
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standard. Single line comments begin with <code><b>//</b></code> and are
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automatically terminated at the end of the current line.
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<hr>
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<center>
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<table border=0 width=100%>
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<tr>
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<td align=left width=20% valign=top>
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<a href="index.html">
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<img src="left.gif" border=0>
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Previous Section<br>
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TOC</a></td>
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<td align=center width=60% valign=top>
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| <a href="index.html">Table of Contents</a> |
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<a href="index2.html">Index</a> |</td>
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<td align=right width=20% valign=top>
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<a href="1.2.html">
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Next Section
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<img src="right.gif" border=0><br>
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1.2 Identifiers</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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