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