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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, simple 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="scanner.html#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>
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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 class="copyright">Copyright © 2002 Jeff Westfahl</p>
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