120 lines
7.6 KiB
HTML
120 lines
7.6 KiB
HTML
<html>
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<title>Position Iterator</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2">
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<td width="10">
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</td>
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<td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Position
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Iterator</b></font> </td>
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<td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" width="112" height="48" align="right" border="0"></a></td>
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</table>
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<br>
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<td width="10"></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td>
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<td width="30"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td>
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<p>Often, when writing a parser that is able to detect errors in the format of
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the input stream, we want it to communicate to the user where the error happened
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within that input. The classic example is when writing a compiler or interpreter
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that detects syntactical errors in the parsed program, indicating the line number
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and maybe even the position within the line where the error was found.</p>
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<p> The class position_iterator is a tool provided within Spirit that allows parser
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writers to easily implement this functionality. The concept is quite simple:
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this class is an iterator wrapper that keeps track of the current position within
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the file, including current file, line and column. It requires a single template
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parameter, which should be the type of the iterator that is to be wrapped.</p>
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<p> To use it, you'll need to add the following include:</p>
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<pre>
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<code><span class=preprocessor>#include </span><span class=special><</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>spirit</span><span class=special>/</span><span class=identifier>iterator</span><span class=special>/</span><span class=identifier>position_iterator</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>></span></code></pre>
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<p> Or include all the iterators in Spirit:</p>
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<pre>
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<code><span class=preprocessor>#include </span><span class=special><</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>spirit</span><span class=special>/</span><span class=identifier>iterator</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>></span></code></pre>
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<p> To construct the wrapper, it needs both the begin and end iterators of the
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input sequence, and the file name of the input sequence. Optionally, you can
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also specify the starting line and column numbers, which default to 1. Default
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construction, with no parameters, creates a generic end-of-sequence iterator,
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in a similar manner as it's done in the stream operators of the standard C++
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library.</p>
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<p> The wrapped iterator must belong to the input or forward iterator category,
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and the position_iterator just inherits that category.</p>
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<p> For example, to create begin and end positional iterators from an input C-
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string, you'd use:</p>
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<pre>
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<code><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>inputstring </span><span class=special>= </span><span class=string>"..."</span><span class=special>;
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</span><span class=keyword>typedef </span><span class=identifier>position_iterator</span><span class=special><</span><span class=keyword>char </span><span class=keyword>const</span><span class=special>*> </span><span class=identifier>iterator_t</span><span class=special>;
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</span><span class=identifier>iterator_t </span><span class=identifier>begin</span><span class=special>(</span><span class=identifier>inputstring</span><span class=special>, </span><span class=identifier>inputstring</span><span class=special>+</span><span class=identifier>strlen</span><span class=special>(</span><span class=identifier>inputstring</span><span class=special>));
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</span><span class=identifier>iterator_t </span><span class=identifier>end</span><span class=special>;</span></code></pre>
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<a name="operations"></a>
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<h2>Operations</h2>
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<pre>
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<code><span class=keyword>void </span><span class=identifier>set_position</span><span class=special>(</span><span class=identifier>file_position </span><span class=keyword>const</span><span class=special>&);</span></code></pre>
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<p> Call this function when you need to change the current position stored in
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the iterator. For example, if parsing C-style #include directives, the included
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file's input must be marked by restarting the file and column to 1 and 1 and
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the name to the new file's name.<br>
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</p>
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<pre>
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<code><span class=identifier>file_position </span><span class=keyword>const</span><span class=special>& </span><span class=identifier>get_position</span><span class=special>() </span><span class=keyword>const</span><span class=special>;</span></code></pre>
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<p> Call this function to retrieve the current position.</p>
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<pre>
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<code><span class=keyword>void </span><span class=identifier>set_tabchars</span><span class=special>(</span><span class=keyword>int</span><span class=special>);</span></code></pre>
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<p> Call this to set the number of tabs per character. This value is necessary
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to correctly track the column number.<br>
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</p>
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<p> <a name="file_position"></a> </p>
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<h2>file_position</h2>
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<p> file_position is a structure that holds the position within a file. Its fields
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are:</p>
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<table width="90%" border="0" align="center">
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<tr>
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<td class="table_title" colspan="2">file_position fields</td>
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</tr>
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<tr>
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<td class="table_cells" width="26%"><code><span class=identifier>std</span><span class=special>::</span><span class=identifier>string
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</span><span class=identifier>file</span><span class=special>;</span></code></td>
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<td class="table_cells" width="74%">Name of the file. Hopefully a full pathname</td>
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</tr>
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<tr>
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<td class="table_cells" width="26%"><code><span class=keyword>int</span><span class=identifier>
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line</span><span class=special>;</span></code></td>
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<td class="table_cells" width="74%">Line number within the file. By default,
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the first line is number 1</td>
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</tr>
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<tr>
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<td class="table_cells" width="26%"><code><span class=keyword>int </span><span class=identifier>column</span><span class=special>;</span></code></td>
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<td class="table_cells" width="74%">Column position within the file. The first
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column is 1</td>
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</tr>
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</table>
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<p><img src="theme/lens.gif" width="15" height="16"> See <a href="../example/fundamental/position_iterator/position_iterator.cpp">position_iterator.cpp</a> for a compilable example. This is part of the Spirit distribution.</p>
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<table border="0">
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<tr>
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<td width="10"></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td>
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<td width="30"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td>
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</tr>
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</table>
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<hr size="1">
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<p class="copyright">Copyright © 2002 Juan Carlos Arevalo-Baeza<br>
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<br>
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<font size="2">Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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<p class="copyright"> </p>
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<p> </p>
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</body>
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</html>
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