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| <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>File Iterator</b></font> |
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| <p>Since Spirit is a back-tracking parser, it requires at least a forward iterator. |
| In particular, an input iterator is not sufficient. Many times it is convenient |
| to read the input to a parser from a file, but the STL file iterators are input |
| iterators. To get around this limitation, Spirit has a utility class <tt>file_iterator</tt>, |
| which is a read-only random-access iterator for files.</p> |
| <p>To use the Spirit file iterator, simply create a file iterator with the path |
| to the file you wish to parse, and then create an EOF iterator for the file:</p> |
| <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> |
| <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>); |
| |
| </span><span class=keyword>if </span><span class=special>(!</span><span class=identifier>first</span><span class=special>) |
| { |
| </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>; |
| |
| </span><span class=comment>// Clean up, throw an exception, whatever |
| </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>; |
| } |
| |
| </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> |
| <p>You now have a pair of iterators to use with Spirit . If your parser is fully |
| parametrized (no hard-coded <tt><char const *></tt>), it is a simple matter |
| of redefining the iterator type to <tt>file_iterator</tt>:<br> |
| </p> |
| <pre> <span class=keyword>typedef char </span><span class="identifier">char_t</span><span class=special>; |
| </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>; |
| </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>; |
| </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>; |
| |
| </span><span class=identifier>rule_t my_rule</span><span class=special>; |
| |
| </span><span class=comment>// Define your rule |
| |
| </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> |
| <p>Of course, you don't have to deal with the <a href="faq.html#scanner_business">scanner-business</a> |
| at all if you use grammars rather than rules as arguments to the parse functions. |
| You simply pass the iterator pairs and the grammar as is:<span class=special><br> |
| </span></p> |
| <pre> <span class=identifier>my_grammar </span><span class=identifier>g</span><span class=special>; |
| </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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| Generic iterator</b><br> |
| <br> |
| The Spirit file iterator can be parameterized with any type that is default |
| constructible and assignable. It transparently supports large files (greater |
| than 2GB) on systems that provide an appropriate interface. The file iterator |
| can be useful outside of Spirit as well. For instance, the Boost.Tokenizer |
| package requires a bidirectional iterator, which is provided by file_iterator.</td> |
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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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| <p class="copyright">Copyright © 2002 Jeff Westfahl</p> |
| <p class="copyright"><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) |
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