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<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<meta name="GENERATOR" content="Microsoft FrontPage Express 2.0">
<title>Boost Char Separator</title>
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--
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-- and its documentation for any purpose is hereby granted without fee,
-- provided that the above copyright notice appears in all copies and
-- that both that copyright notice and this permission notice appear
-- in supporting documentation. Jeremy Siek makes no
-- representations about the suitability of this software for any
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</head>
<body bgcolor="#FFFFFF" text="#000000" link="#0000EE"
vlink="#551A8B" alink="#FF0000">
<p><img src="../../c++boost.gif" alt="C++ Boost" width="277"
height="86"> <br>
</p>
<h1>
char_separator<Char, Traits>
</h1>
<p>
The <tt>char_separator</tt> class breaks a sequence of characters into
tokens based on character delimiters much in the same way that
<tt>strtok()</tt> does (but without all the evils of non-reentrancy
and destruction of the input sequence).
</p>
<p>
The <tt>char_separator</tt> class is used in conjunction with the <a
href="token_iterator.htm"><tt>token_iterator</tt></a> or <a
href="tokenizer.htm"><tt>tokenizer</tt></a> to perform tokenizing.
</p>
<h2>Definitions</h2>
<p>
The <tt>strtok()</tt> function does not include matches with the
character delimiters in the output sequence of tokens. However,
sometimes it is useful to have the delimiters show up in the output
sequence, therefore <tt>char_separator</tt> provides this as an
option. We refer to delimiters that show up as output tokens as
<b><i>kept delimiters</i></b> and delimiters that do now show up as
output tokens as <b><i>dropped delimiters</i></b>.
</p>
<p>
When two delimiters appear next to each other in the input sequence,
there is the question of whether to output an <b><i>empty
token</i></b> or to skip ahead. The behaviour of <tt>strtok()</tt> is
to skip ahead. The <tt>char_separator</tt> class provides both
options.
</p>
<h2>Examples</h2>
<p>
This first examples shows how to use <tt>char_separator</tt> as a
replacement for the <tt>strtok()</tt> function. We've specified three
character delimiters, and they will not show up as output tokens. We
have not specified any kept delimiters, and by default any empty
tokens will be ignored.
</p>
<blockquote>
<pre>// char_sep_example_1.cpp
#include <iostream>
#include <boost/tokenizer.hpp>
#include <string>
int main()
{
std::string str = ";;Hello|world||-foo--bar;yow;baz|";
typedef boost::tokenizer<boost::char_separator<char> >
tokenizer;
boost::char_separator<char> sep("-;|");
tokenizer tokens(str, sep);
for (tokenizer::iterator tok_iter = tokens.begin();
tok_iter != tokens.end(); ++tok_iter)
std::cout << "<" << *tok_iter << "> ";
std::cout << "\n";
return EXIT_SUCCESS;
}
</pre>
</blockquote>
The output is:
<blockquote>
<pre>
<Hello> <world> <foo> <bar> <yow> <baz>
</pre>
</blockquote>
<p>
The next example shows tokenizing with two dropped delimiters '-' and
';' and a single kept delimiter '|'. We also specify that empty tokens
should show up in the output when two delimiters are next to each
other.
</p>
<blockquote>
<pre>// char_sep_example_2.cpp
#include <iostream>
#include <boost/tokenizer.hpp>
#include <string>
int main()
{
std::string str = ";;Hello|world||-foo--bar;yow;baz|";
typedef boost::tokenizer<boost::char_separator<char> >
tokenizer;
boost::char_separator<char> sep("-;", "|", boost::keep_empty_tokens);
tokenizer tokens(str, sep);
for (tokenizer::iterator tok_iter = tokens.begin();
tok_iter != tokens.end(); ++tok_iter)
std::cout << "<" << *tok_iter << "> ";
std::cout << "\n";
return EXIT_SUCCESS;
}
</pre>
</blockquote>
The output is:
<blockquote>
<pre>
<> <> <Hello> <|> <world> <|> <> <|> <> <foo> <> <bar> <yow> <baz> <|> <>
</pre>
</blockquote>
<p>
The final example shows tokenizing on punctuation and whitespace
characters using the default constructor of the
<tt>char_separator</tt>.
</p>
<blockquote>
<pre>// char_sep_example_3.cpp
#include <iostream>
#include <boost/tokenizer.hpp>
#include <string>
int main()
{
std::string str = "This is, a test";
typedef boost::tokenizer<boost::char_separator<char> > Tok;
boost::char_separator<char> sep; // default constructed
Tok tok(str, sep);
for(Tok::iterator tok_iter = tok.begin(); tok_iter != tok.end(); ++tok_iter)
std::cout << "<" << *tok_iter << "> ";
std::cout << "\n";
return EXIT_SUCCESS;
}
</pre>
</blockquote>
The output is:
<blockquote>
<pre>
<This> <is> <,> <a> <test>
</pre>
</blockquote>
<h2>Template parameters</h2>
<P>
<table border>
<TR>
<th>Parameter</th><th>Description</th><th>Default</th>
</tr>
<TR><TD><TT>Char</TT></TD>
<TD>The type of elements within a token, typically <tt>char</tt>.</TD>
<TD> </TD>
</TR>
<TR><TD><TT>Traits</TT></TD>
<TD>The <tt>char_traits</tt> for the character type.</TD>
<TD><tt>char_traits<char></tt></TD>
</TR>
</table>
<h2>Model of</h2>
<a href="tokenizerfunction.htm">Tokenizer Function</a>
<h2>Members</h2>
<hr>
<pre>
explicit char_separator(const Char* dropped_delims,
const Char* kept_delims = "",
empty_token_policy empty_tokens = drop_empty_tokens)
</pre>
<p>
This creates a <tt>char_separator</tt> object, which can then be used
to create a <a href="token_iterator.htm"><tt>token_iterator</tt></a>
or <a href="tokenizer.htm"><tt>tokenizer</tt></a> to perform
tokenizing. The <tt>dropped_delims</tt> and <tt>kept_delims</tt> are
strings of characters where each character is used as delimiter during
tokenizing. Whenever a delimiter is seen in the input sequence, the
current token is finished, and a new token begins.
The delimiters in <tt>dropped_delims</tt> do not show up as tokens in
the output whereas the delimiters in <tt>kept_delims</tt> do show up
as tokens. If <tt>empty_tokens</tt> is <tt>drop_empty_tokens</tt>,
then empty tokens will not show up in the output. If
<tt>empty_tokens</tt> is <tt>keep_empty_tokens</tt> then empty tokens
will show up in the output.
</p>
<hr>
<pre>
explicit char_separator()
</pre>
<p>
The function <tt>std::isspace()</tt> is used to identify dropped
delimiters and <tt>std::ispunct()</tt> is used to identify kept
delimiters. In addition, empty tokens are dropped.
</p>
<hr>
<pre>
template <typename InputIterator, typename Token>
bool operator()(InputIterator& next, InputIterator end, Token& tok)
</pre>
<p>
This function is called by the <a
href="token_iterator.htm"><tt>token_iterator</tt></a> to perform
tokenizing. The user typically does not call this function directly.
</p>
<hr>
<p> Copyright Jeremy Siek and John R. Bandela 2001-2002. Permission
to copy, use, modify, sell and distribute this document is granted
provided this copyright notice appears in all copies. This document is
provided "as is" without express or implied warranty, and
with no claim as to its suitability for any purpose.</p>
</body>
</html>
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