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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> |
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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 © 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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