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