doc/stdlibug/8-3.html - stdcxx - Git at Google

 <!--
     Licensed to the Apache Software  Foundation (ASF) under one or more
     contributor  license agreements.  See  the NOTICE  file distributed
     with  this  work  for  additional information  regarding  copyright
     ownership.   The ASF  licenses this  file to  you under  the Apache
     License, Version  2.0 (the  License); you may  not use  this file
     except in  compliance with the License.   You may obtain  a copy of
     the License at

     http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software
     distributed under the  License is distributed on an  "AS IS" BASIS,
     WITHOUT  WARRANTIES OR CONDITIONS  OF ANY  KIND, either  express or
     implied.   See  the License  for  the  specific language  governing
     permissions and limitations under the License.

     Copyright 1999-2007 Rogue Wave Software, Inc.
 -->

 <HTML>
 <HEAD>
 <TITLE>Example Program: A Spelling Checker</TITLE>
 <LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
 <BODY BGCOLOR=#FFFFFF>
 <A HREF="8-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="8-4.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV>
 <H2>8.3 Example Program: A Spelling Checker</H2>
 <A NAME="idx150"><!></A>
 <P>A simple example program that uses a <B><I><A HREF="../stdlibref/set.html">set</A></I></B> is a spelling checker. </P>
 <BLOCKQUOTE><HR><B>
 NOTE -- This program can be found in the file spell.cpp.
 </B><HR></BLOCKQUOTE>
 <P>The checker takes as arguments two input streams: the first represents a stream of correctly spelled words (that is, a dictionary), and the second a text file. To begin, the dictionary is read into a set. This is performed with a <SAMP>std::copy()</SAMP> function and an input stream iterator, copying the values into an inserter for the dictionary. Next, words from the text are examined one by one, to see if they are in the dictionary. If they are not, they are added to a set of misspelled words. After the entire text has been examined, the program outputs the list of misspelled words.</P>

 <UL><PRE>
 typedef
   std::set &lt;std::string,
             std::less&lt;std::string&gt;, std::allocator&lt;std::string&gt; &gt;
   stringset;

 typedef
   std::ostream_iterator&lt;std::string, char, std::char_traits&lt;char&gt; &gt;
   ostrm_iter;

 typedef
   std::istream_iterator&lt;std::string,
                         char, std::char_traits&lt;char&gt;, ptrdiff_t&gt;
   istrm_iter;

 void spellCheck (istream&amp; dictionary, istream&amp; text) {
   stringset words, misspellings;
   std::string word;
   istrm_iter  eof, dstream (dictionary);

   // First read the dictionary.
   std::copy (dstream, eof, std::inserter (words, words.begin ()));

   // Next read the text.
   while (text &gt;&gt; word)
     if (! words.count (word))
       misspellings.insert (word);

   // Finally, output all misspellings.
   std::cout &lt;&lt; std::endl &lt;&lt; "Misspelled words:" &lt;&lt; std::endl;

   std::copy (misspellings.begin (), misspellings.end (),
              ostrm_iter (std::cout, "\n"));
 }
 </PRE></UL>
 <P>An improvement would be to suggest alternative words for each misspelling. There are various heuristics that can be used to discover alternatives. The technique we use here is to simply exchange adjacent letters. To find these, a call to the following function is inserted into the loop that displays the misspellings:</P>

 <UL><PRE>{
   for (int I = 1; I &lt; word.length(); I++) {
     std::swap(word[I-1], word[I]);
     if (words.count(word))
       std::cout &lt;&lt; "Suggestion: " &lt;&lt; word &lt;&lt; std::endl;
     // put word back as before
     std::swap(word[I-1], word[I]);
     }
 }
 </PRE></UL>

 <BR>
 <HR>
 <A HREF="8-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="8-4.html"><IMG SRC="images/bnext.gif" WIDTH=20 HEIGHT=21 ALT="Next file" BORDER=O></A>

 <!-- Google Analytics tracking code -->
 <script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
 </script>
 <script type="text/javascript">
     _uacct = "UA-1775151-1";
     urchinTracker();
 </script>
 <!-- end of Google Analytics tracking code -->

 </BODY>
 </HTML>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed
	with this work for additional information regarding copyright
	ownership. The ASF licenses this file to you under the Apache
	License, Version 2.0 (the License); you may not use this file
	except in compliance with the License. You may obtain a copy of
	the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
	implied. See the License for the specific language governing
	permissions and limitations under the License.

	Copyright 1999-2007 Rogue Wave Software, Inc.
	-->

	<HTML>
	<HEAD>
	<TITLE>Example Program: A Spelling Checker</TITLE>
	<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
	<BODY BGCOLOR=#FFFFFF>
	<A HREF="8-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="8-4.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV>
	<H2>8.3 Example Program: A Spelling Checker</H2>
	<A NAME="idx150"><!></A>
	<P>A simple example program that uses a <B><I><A HREF="../stdlibref/set.html">set</A></I></B> is a spelling checker. </P>
	<BLOCKQUOTE><HR><B>
	NOTE -- This program can be found in the file spell.cpp.
	</B><HR></BLOCKQUOTE>
	<P>The checker takes as arguments two input streams: the first represents a stream of correctly spelled words (that is, a dictionary), and the second a text file. To begin, the dictionary is read into a set. This is performed with a <SAMP>std::copy()</SAMP> function and an input stream iterator, copying the values into an inserter for the dictionary. Next, words from the text are examined one by one, to see if they are in the dictionary. If they are not, they are added to a set of misspelled words. After the entire text has been examined, the program outputs the list of misspelled words.</P>

	<UL><PRE>
	typedef
	std::set <std::string,
	std::less<std::string>, std::allocator<std::string> >
	stringset;

	typedef
	std::ostream_iterator<std::string, char, std::char_traits<char> >
	ostrm_iter;

	typedef
	std::istream_iterator<std::string,
	char, std::char_traits<char>, ptrdiff_t>
	istrm_iter;

	void spellCheck (istream& dictionary, istream& text) {
	stringset words, misspellings;
	std::string word;
	istrm_iter eof, dstream (dictionary);

	// First read the dictionary.
	std::copy (dstream, eof, std::inserter (words, words.begin ()));

	// Next read the text.
	while (text >> word)
	if (! words.count (word))
	misspellings.insert (word);

	// Finally, output all misspellings.
	std::cout << std::endl << "Misspelled words:" << std::endl;

	std::copy (misspellings.begin (), misspellings.end (),
	ostrm_iter (std::cout, "\n"));
	}
	</PRE></UL>
	<P>An improvement would be to suggest alternative words for each misspelling. There are various heuristics that can be used to discover alternatives. The technique we use here is to simply exchange adjacent letters. To find these, a call to the following function is inserted into the loop that displays the misspellings:</P>

	<UL><PRE>{
	for (int I = 1; I < word.length(); I++) {
	std::swap(word[I-1], word[I]);
	if (words.count(word))
	std::cout << "Suggestion: " << word << std::endl;
	// put word back as before
	std::swap(word[I-1], word[I]);
	}
	}
	</PRE></UL>

	<BR>
	<HR>
	<A HREF="8-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="8-4.html"><IMG SRC="images/bnext.gif" WIDTH=20 HEIGHT=21 ALT="Next file" BORDER=O></A>

	<!-- Google Analytics tracking code -->
	<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
	</script>
	<script type="text/javascript">
	_uacct = "UA-1775151-1";
	urchinTracker();
	</script>
	<!-- end of Google Analytics tracking code -->

	</BODY>
	</HTML>