| 1 | <html> |
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| 2 | <head> |
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| 3 | <title>Position Iterator</title> |
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| 7 | |
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| 8 | <body> |
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| 9 | <table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2"> |
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| 10 | <tr> |
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| 11 | <td width="10"> |
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| 12 | </td> |
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| 13 | <td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Position |
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| 14 | Iterator</b></font> </td> |
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| 15 | <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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| 16 | </tr> |
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| 17 | </table> |
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| 18 | <br> |
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| 19 | <table border="0"> |
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| 20 | <tr> |
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| 21 | <td width="10"></td> |
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| 22 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> |
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| 23 | <td width="30"><a href="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td> |
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| 24 | <td width="30"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td> |
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| 25 | </tr> |
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| 26 | </table> |
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| 27 | <p>Often, when writing a parser that is able to detect errors in the format of |
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| 28 | the input stream, we want it to communicate to the user where the error happened |
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| 29 | within that input. The classic example is when writing a compiler or interpreter |
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| 30 | that detects syntactical errors in the parsed program, indicating the line number |
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| 31 | and maybe even the position within the line where the error was found.</p> |
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| 32 | <p> The class position_iterator is a tool provided within Spirit that allows parser |
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| 33 | writers to easily implement this functionality. The concept is quite simple: |
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| 34 | this class is an iterator wrapper that keeps track of the current position within |
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| 35 | the file, including current file, line and column. It requires a single template |
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| 36 | parameter, which should be the type of the iterator that is to be wrapped.</p> |
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| 37 | <p> To use it, you'll need to add the following include:</p> |
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| 38 | <pre> |
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| 39 | <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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| 40 | <p> Or include all the iterators in Spirit:</p> |
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| 41 | <pre> |
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| 42 | <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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| 43 | <p> To construct the wrapper, it needs both the begin and end iterators of the |
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| 44 | input sequence, and the file name of the input sequence. Optionally, you can |
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| 45 | also specify the starting line and column numbers, which default to 1. Default |
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| 46 | construction, with no parameters, creates a generic end-of-sequence iterator, |
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| 47 | in a similar manner as it's done in the stream operators of the standard C++ |
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| 48 | library.</p> |
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| 49 | <p> The wrapped iterator must belong to the input or forward iterator category, |
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| 50 | and the position_iterator just inherits that category.</p> |
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| 51 | <p> For example, to create begin and end positional iterators from an input C- |
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| 52 | string, you'd use:</p> |
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| 53 | <pre> |
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| 54 | <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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| 55 | </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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| 56 | |
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| 57 | </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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| 58 | </span><span class=identifier>iterator_t </span><span class=identifier>end</span><span class=special>;</span></code></pre> |
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| 59 | <a name="operations"></a> |
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| 60 | <h2>Operations</h2> |
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| 61 | <pre> |
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| 62 | <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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| 63 | <p> Call this function when you need to change the current position stored in |
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| 64 | the iterator. For example, if parsing C-style #include directives, the included |
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| 65 | file's input must be marked by restarting the file and column to 1 and 1 and |
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| 66 | the name to the new file's name.<br> |
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| 67 | </p> |
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| 68 | <pre> |
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| 69 | <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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| 70 | <p> Call this function to retrieve the current position.</p> |
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| 71 | <pre> |
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| 72 | <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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| 73 | <p> Call this to set the number of tabs per character. This value is necessary |
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| 74 | to correctly track the column number.<br> |
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| 75 | </p> |
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| 76 | <p> <a name="file_position"></a> </p> |
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| 77 | <h2>file_position</h2> |
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| 78 | <p> file_position is a structure that holds the position within a file. Its fields |
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| 79 | are:</p> |
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| 80 | <table width="90%" border="0" align="center"> |
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| 81 | <tr> |
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| 82 | <td class="table_title" colspan="2">file_position fields</td> |
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| 83 | </tr> |
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| 84 | <tr> |
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| 85 | <td class="table_cells" width="26%"><code><span class=identifier>std</span><span class=special>::</span><span class=identifier>string |
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| 86 | </span><span class=identifier>file</span><span class=special>;</span></code></td> |
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| 87 | <td class="table_cells" width="74%">Name of the file. Hopefully a full pathname</td> |
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| 88 | </tr> |
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| 89 | <tr> |
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| 90 | <td class="table_cells" width="26%"><code><span class=keyword>int</span><span class=identifier> |
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| 91 | line</span><span class=special>;</span></code></td> |
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| 92 | <td class="table_cells" width="74%">Line number within the file. By default, |
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| 93 | the first line is number 1</td> |
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| 94 | </tr> |
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| 95 | <tr> |
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| 96 | <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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| 97 | <td class="table_cells" width="74%">Column position within the file. The first |
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| 98 | column is 1</td> |
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| 99 | </tr> |
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| 100 | </table> |
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| 101 | <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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| 102 | <table border="0"> |
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| 103 | <tr> |
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| 104 | <td width="10"></td> |
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| 105 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> |
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| 106 | <td width="30"><a href="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td> |
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| 107 | <td width="30"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td> |
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| 108 | </tr> |
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| 109 | </table> |
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| 110 | <hr size="1"> |
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| 111 | <p class="copyright">Copyright © 2002 Juan Carlos Arevalo-Baeza<br> |
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| 112 | <br> |
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| 113 | <font size="2">Use, modification and distribution is subject to the Boost Software |
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| 114 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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| 115 | http://www.boost.org/LICENSE_1_0.txt) </font> </p> |
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| 116 | <p class="copyright"> </p> |
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| 117 | <p> </p> |
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| 118 | </body> |
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| 119 | </html> |
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