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<title>Regex++, Format String Reference</title>
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<p> </p>
<table border="0" cellpadding="7" cellspacing="0" width="100%">
<tr>
<td valign="top"><h3><img src="../../c++boost.gif"
alt="C++ Boost" width="276" height="86"></h3>
</td>
<td valign="top"><h3 align="center">Regex++, Format
String Reference.</h3>
<p align="left"><i>Copyright (c) 1998-2001 </i></p>
<p align="left"><i>Dr John Maddock</i></p>
<p align="left"><i>Permission to use, copy, modify,
distribute and sell this software and its documentation
for any purpose is hereby granted without fee, provided
that the above copyright notice appear in all copies and
that both that copyright notice and this permission
notice appear in supporting documentation. Dr John
Maddock makes no representations about the suitability of
this software for any purpose. It is provided "as is"
without express or implied warranty.</i></p>
</td>
</tr>
</table>
<hr>
<h3><a name="format_string"></a>Format String Syntax</h3>
<p>Format strings are used by the algorithms <a
href="template_class_ref.htm#reg_format">regex_format</a> and <a
href="template_class_ref.htm#reg_merge">regex_merge</a>, and are
used to transform one string into another. </p>
<p>There are three kind of format string: sed, perl and extended,
the extended syntax is the default so this is covered first. </p>
<p><b><i>Extended format syntax</i></b> </p>
<p>In format strings, all characters are treated as literals
except: ()$\?: </p>
<p>To use any of these as literals you must prefix them with the
escape character \ </p>
<p>The following special sequences are recognized: <br>
<br>
</p>
<p><i>Grouping:</i> </p>
<p>Use the parenthesis characters ( and ) to group sub-expressions
within the format string, use \( and \) to represent literal '('
and ')'. <br>
<br>
</p>
<p><i>Sub-expression expansions:</i> </p>
<p>The following perl like expressions expand to a particular
matched sub-expression: <br>
</p>
<table border="0" cellpadding="7" cellspacing="0" width="100%">
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">$`</td>
<td valign="top" width="43%">Expands to all the text from
the end of the previous match to the start of the current
match, if there was no previous match in the current
operation, then everything from the start of the input
string to the start of the match.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">$'</td>
<td valign="top" width="43%">Expands to all the text from
the end of the match to the end of the input string.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">$&</td>
<td valign="top" width="43%">Expands to all of the
current match.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">$0</td>
<td valign="top" width="43%">Expands to all of the
current match.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">$N</td>
<td valign="top" width="43%">Expands to the text that
matched sub-expression <i>N</i>.</td>
<td valign="top" width="9%"> </td>
</tr>
</table>
<p><br>
</p>
<p><i>Conditional expressions:</i> </p>
<p>Conditional expressions allow two different format strings to
be selected dependent upon whether a sub-expression participated
in the match or not: </p>
<p>?Ntrue_expression:false_expression </p>
<p>Executes true_expression if sub-expression <i>N</i>
participated in the match, otherwise executes false_expression. </p>
<p>Example: suppose we search for "(while)|(for)" then
the format string "?1WHILE:FOR" would output what
matched, but in upper case. <br>
<br>
</p>
<p><i>Escape sequences:</i> </p>
<p>The following escape sequences are also allowed: <br>
</p>
<table border="0" cellpadding="7" cellspacing="0" width="100%">
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\a</td>
<td valign="top" width="43%">The bell character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\f</td>
<td valign="top" width="43%">The form feed character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\n</td>
<td valign="top" width="43%">The newline character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\r</td>
<td valign="top" width="43%">The carriage return
character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\t</td>
<td valign="top" width="43%">The tab character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\v</td>
<td valign="top" width="43%">A vertical tab character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\x</td>
<td valign="top" width="43%">A hexadecimal character -
for example \x0D.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\x{}</td>
<td valign="top" width="43%">A possible unicode
hexadecimal character - for example \x{1A0}</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\cx</td>
<td valign="top" width="43%">The ASCII escape character
x, for example \c@ is equivalent to escape-@.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\e</td>
<td valign="top" width="43%">The ASCII escape character.</td>
<td valign="top" width="9%"> </td>
</tr>
<tr>
<td valign="top" width="8%"> </td>
<td valign="top" width="40%">\dd</td>
<td valign="top" width="43%">An octal character constant,
for example \10.</td>
<td valign="top" width="9%"> </td>
</tr>
</table>
<p><br>
</p>
<p><b><i>Perl format strings</i></b> </p>
<p>Perl format strings are the same as the default syntax except
that the characters ()?: have no special meaning. </p>
<p><b><i>Sed format strings</i></b> </p>
<p>Sed format strings use only the characters \ and & as
special characters. </p>
<p>\n where n is a digit, is expanded to the nth sub-expression. </p>
<p>& is expanded to the whole of the match (equivalent to \0).
</p>
<p>Other escape sequences are expanded as per the default syntax.
<br>
</p>
<hr>
<p><i>Copyright </i><a href="mailto:John_Maddock@compuserve.com"><i>Dr
John Maddock</i></a><i> 1998-2000 all rights reserved.</i> </p>
</body>
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