98 lines
7.1 KiB
HTML
98 lines
7.1 KiB
HTML
<html>
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<head>
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<title>File Iterator</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" href="theme/style.css" type="text/css">
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</head>
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<body>
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<table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2">
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<tr>
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<td width="10">
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</td>
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<td width="85%">
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>File Iterator</b></font>
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</td>
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<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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</tr>
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</table>
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<br>
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<table border="0">
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<tr>
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<td width="10"></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="multi_pass.html"><img src="theme/l_arr.gif" border="0"></a></td>
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<td width="30"><a href="position_iterator.html"><img src="theme/r_arr.gif" border="0"></a></td>
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</tr>
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</table>
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<p>Since Spirit is a back-tracking parser, it requires at least a forward iterator.
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In particular, an input iterator is not sufficient. Many times it is convenient
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to read the input to a parser from a file, but the STL file iterators are input
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iterators. To get around this limitation, Spirit has a utility class <tt>file_iterator</tt>,
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which is a read-only random-access iterator for files.</p>
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<p>To use the Spirit file iterator, simply create a file iterator with the path
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to the file you wish to parse, and then create an EOF iterator for the file:</p>
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<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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<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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</span><span class=keyword>if </span><span class=special>(!</span><span class=identifier>first</span><span class=special>)
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{
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</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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</span><span class=comment>// Clean up, throw an exception, whatever
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</span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>;
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}
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</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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<p>You now have a pair of iterators to use with Spirit . If your parser is fully
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parametrized (no hard-coded <tt><char const *></tt>), it is a simple matter
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of redefining the iterator type to <tt>file_iterator</tt>:<br>
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</p>
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<pre> <span class=keyword>typedef char </span><span class="identifier">char_t</span><span class=special>;
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</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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</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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</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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</span><span class=identifier>rule_t my_rule</span><span class=special>;
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</span><span class=comment>// Define your rule
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</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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<p>Of course, you don't have to deal with the <a href="faq.html#scanner_business">scanner-business</a>
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at all if you use grammars rather than rules as arguments to the parse functions.
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You simply pass the iterator pairs and the grammar as is:<span class=special><br>
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</span></p>
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<pre> <span class=identifier>my_grammar </span><span class=identifier>g</span><span class=special>;
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</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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<table width="80%" border="0" align="center">
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<tr>
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<td class="note_box"><img src="theme/bulb.gif" width="13" height="18"><b>
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Generic iterator</b><br>
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<br>
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The Spirit file iterator can be parameterized with any type that is default
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constructible and assignable. It transparently supports large files (greater
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than 2GB) on systems that provide an appropriate interface. The file iterator
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can be useful outside of Spirit as well. For instance, the Boost.Tokenizer
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package requires a bidirectional iterator, which is provided by file_iterator.</td>
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</tr>
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</table>
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<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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<table border="0">
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<tr>
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<td width="10"></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="multi_pass.html"><img src="theme/l_arr.gif" border="0"></a></td>
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<td width="30"><a href="position_iterator.html"><img src="theme/r_arr.gif" border="0"></a></td>
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</tr>
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</table>
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<br>
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<hr size="1">
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<p class="copyright">Copyright © 2002 Jeff Westfahl</p>
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<p class="copyright"><font size="2"> Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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</font> </p>
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<p class="copyright"> </p>
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</body>
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</html>
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