| 1 | <html> |
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| 2 | <head> |
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| 3 | <title>File Iterator</title> |
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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%"> |
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| 14 | <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>File Iterator</b></font> |
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| 15 | </td> |
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| 16 | <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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| 17 | </tr> |
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| 18 | </table> |
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| 19 | <br> |
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| 20 | <table border="0"> |
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| 21 | <tr> |
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| 22 | <td width="10"></td> |
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| 23 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> |
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| 24 | <td width="30"><a href="multi_pass.html"><img src="theme/l_arr.gif" border="0"></a></td> |
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| 25 | <td width="30"><a href="position_iterator.html"><img src="theme/r_arr.gif" border="0"></a></td> |
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| 26 | </tr> |
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| 27 | </table> |
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| 28 | <p>Since Spirit is a back-tracking parser, it requires at least a forward iterator. |
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| 29 | In particular, an input iterator is not sufficient. Many times it is convenient |
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| 30 | to read the input to a parser from a file, but the STL file iterators are input |
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| 31 | iterators. To get around this limitation, Spirit has a utility class <tt>file_iterator</tt>, |
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| 32 | which is a read-only random-access iterator for files.</p> |
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| 33 | <p>To use the Spirit file iterator, simply create a file iterator with the path |
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| 34 | to the file you wish to parse, and then create an EOF iterator for the file:</p> |
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| 35 | <pre><span class=identifier> </span><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>file_iterator</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>> </span><span class=comment>// the header file</span></pre> |
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| 36 | <pre> <span class=identifier>file_iterator</span><span class=special><> </span><span class=identifier>first</span><span class=special>(</span><span class=string>"input.dat"</span><span class=special>); |
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| 37 | |
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| 38 | </span><span class=keyword>if </span><span class=special>(!</span><span class=identifier>first</span><span class=special>) |
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| 39 | { |
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| 40 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=string>"Unable to open file!\n"</span><span class=special>; |
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| 41 | |
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| 42 | </span><span class=comment>// Clean up, throw an exception, whatever |
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| 43 | </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>; |
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| 44 | } |
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| 45 | |
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| 46 | </span><span class=identifier>file_iterator</span><span class=special><> </span><span class=identifier>last </span><span class=special>= </span><span class=identifier>first</span><span class=special>.</span><span class=identifier>make_end</span><span class=special>();</span></pre> |
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| 47 | <p>You now have a pair of iterators to use with Spirit . If your parser is fully |
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| 48 | parametrized (no hard-coded <tt><char const *></tt>), it is a simple matter |
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| 49 | of redefining the iterator type to <tt>file_iterator</tt>:<br> |
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| 50 | </p> |
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| 51 | <pre> <span class=keyword>typedef char </span><span class="identifier">char_t</span><span class=special>; |
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| 52 | </span><span class=keyword>typedef </span><span class=identifier>file_iterator </span><span class=special><</span><span class=keyword>char</span><span class=identifier>_t</span><span class=special>> </span><span class=identifier>iterator_t</span><span class=special>; |
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| 53 | </span><span class=keyword>typedef </span><span class=identifier>scanner</span><span class=special><</span><span class=identifier>iterator_t</span><span class=special>> </span><span class=identifier>scanner_t</span><span class=special>; |
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| 54 | </span><span class=keyword>typedef </span><span class=identifier>rule </span><span class=special><</span><span class=identifier>scanner_t</span><span class=special>> </span><span class=identifier>rule_t</span><span class=special>; |
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| 55 | |
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| 56 | </span><span class=identifier>rule_t my_rule</span><span class=special>; |
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| 57 | |
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| 58 | </span><span class=comment>// Define your rule |
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| 59 | |
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| 60 | </span><span class=identifier>parse_info</span><span class=special><</span><span class=identifier>iterator_t</span><span class=special>> </span><span class=identifier>info </span><span class=special>= </span><span class=identifier>parse</span><span class=special>(</span><span class=identifier>first</span><span class=special>, </span><span class=identifier>last</span><span class=special>, </span><span class=identifier>my_rule</span><span class=special>);</span></pre> |
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| 61 | <p>Of course, you don't have to deal with the <a href="faq.html#scanner_business">scanner-business</a> |
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| 62 | at all if you use grammars rather than rules as arguments to the parse functions. |
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| 63 | You simply pass the iterator pairs and the grammar as is:<span class=special><br> |
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| 64 | </span></p> |
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| 65 | <pre> <span class=identifier>my_grammar </span><span class=identifier>g</span><span class=special>; |
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| 66 | </span><span class=identifier>parse_info</span><span class=special><</span><span class=identifier>iterator_t</span><span class=special>> </span><span class=identifier>info </span><span class=special>= </span><span class=identifier>parse</span><span class=special>(</span><span class=identifier>first</span><span class=special>, </span><span class=identifier>last</span><span class=special>, </span><span class=identifier>g</span><span class=special>);</span></pre> |
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| 67 | <table width="80%" border="0" align="center"> |
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| 68 | <tr> |
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| 69 | <td class="note_box"><img src="theme/bulb.gif" width="13" height="18"><b> |
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| 70 | Generic iterator</b><br> |
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| 71 | <br> |
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| 72 | The Spirit file iterator can be parameterized with any type that is default |
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| 73 | constructible and assignable. It transparently supports large files (greater |
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| 74 | than 2GB) on systems that provide an appropriate interface. The file iterator |
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| 75 | can be useful outside of Spirit as well. For instance, the Boost.Tokenizer |
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| 76 | package requires a bidirectional iterator, which is provided by file_iterator.</td> |
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| 77 | </tr> |
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| 78 | </table> |
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| 79 | <p><img src="theme/lens.gif" width="15" height="16"> See <a href="../example/fundamental/file_parser.cpp">file_parser.cpp</a> for a compilable example. This is part of the Spirit distribution.</p> |
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| 80 | <table border="0"> |
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| 81 | <tr> |
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| 82 | <td width="10"></td> |
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| 83 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> |
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| 84 | <td width="30"><a href="multi_pass.html"><img src="theme/l_arr.gif" border="0"></a></td> |
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| 85 | <td width="30"><a href="position_iterator.html"><img src="theme/r_arr.gif" border="0"></a></td> |
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| 86 | </tr> |
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| 87 | </table> |
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| 88 | <br> |
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| 89 | <hr size="1"> |
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| 90 | <p class="copyright">Copyright © 2002 Jeff Westfahl</p> |
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| 91 | <p class="copyright"><font size="2"> Use, modification and distribution is subject to the Boost Software |
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| 92 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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| 93 | http://www.boost.org/LICENSE_1_0.txt) |
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| 94 | </font> </p> |
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| 95 | <p class="copyright"> </p> |
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| 96 | </body> |
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| 97 | </html> |
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