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<title>Position Iterator</title>
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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>&lt;</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>&gt;</span></code></pre>
<p> Or include all the iterators in Spirit:</p>
<pre>
    <code><span class=preprocessor>#include </span><span class=special>&lt;</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>&gt;</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>&quot;...&quot;</span><span class=special>;
    </span><span class=keyword>typedef </span><span class=identifier>position_iterator</span><span class=special>&lt;</span><span class=keyword>char </span><span class=keyword>const</span><span class=special>*&gt; </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>&amp;);</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>&amp; </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>
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    <td class="table_title" colspan="2">file_position fields</td>
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    <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>
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    <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>
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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>
    <td class="table_cells" width="74%">Column position within the file. The first 
      column is 1</td>
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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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<p class="copyright">Copyright &copy; 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>
<p class="copyright">&nbsp; </p>
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