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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_regex.ref.syntax_option_type.syntax_option_type_perl"></a><a class="link" href="syntax_option_type_perl.html" title="Options for Perl Regular Expressions">
Options for Perl Regular Expressions</a>
</h4></div></div></div>
<p>
One of the following must always be set for perl regular expressions:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Element
</p>
</th>
<th>
<p>
Standardized
</p>
</th>
<th>
<p>
Effect when set
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
ECMAScript
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that the grammar recognized by the regular expression
engine uses its normal semantics: that is the same as that given
in the ECMA-262, ECMAScript Language Specification, Chapter 15
part 10, RegExp (Regular Expression) Objects (FWD.1).
</p>
<p>
This is functionally identical to the <a class="link" href="../../syntax/perl_syntax.html" title="Perl Regular Expression Syntax">Perl
regular expression syntax</a>.
</p>
<p>
Boost.Regex also recognizes all of the perl-compatible <code class="computeroutput"><span class="special">(?...)</span></code> extensions in this mode.
</p>
</td>
</tr>
<tr>
<td>
<p>
perl
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
As above.
</p>
</td>
</tr>
<tr>
<td>
<p>
normal
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
As above.
</p>
</td>
</tr>
<tr>
<td>
<p>
JavaScript
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
As above.
</p>
</td>
</tr>
<tr>
<td>
<p>
JScript
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
As above.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The following options may also be set when using perl-style regular expressions:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Element
</p>
</th>
<th>
<p>
Standardized
</p>
</th>
<th>
<p>
Effect when set
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
icase
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that matching of regular expressions against a character
container sequence shall be performed without regard to case.
</p>
</td>
</tr>
<tr>
<td>
<p>
nosubs
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that when a regular expression is matched against a
character container sequence, then no sub-expression matches
are to be stored in the supplied <a class="link" href="../match_results.html" title="match_results"><code class="computeroutput"><span class="identifier">match_results</span></code></a> structure.
</p>
</td>
</tr>
<tr>
<td>
<p>
optimize
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that the regular expression engine should pay more
attention to the speed with which regular expressions are matched,
and less to the speed with which regular expression objects are
constructed. Otherwise it has no detectable effect on the program
output. This currently has no effect for Boost.Regex.
</p>
</td>
</tr>
<tr>
<td>
<p>
collate
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that character ranges of the form <code class="computeroutput"><span class="special">[</span><span class="identifier">a</span><span class="special">-</span><span class="identifier">b</span><span class="special">]</span></code>
should be locale sensitive.
</p>
</td>
</tr>
<tr>
<td>
<p>
newline_alt
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Specifies that the \n character has the same effect as the alternation
operator |. Allows newline separated lists to be used as a list
of alternatives.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_except
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Prevents <a class="link" href="../basic_regex.html" title="basic_regex"><code class="computeroutput"><span class="identifier">basic_regex</span></code></a> from throwing
an exception when an invalid expression is encountered.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_mod_m
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Normally Boost.Regex behaves as if the Perl m-modifier is on:
so the assertions ^ and $ match after and before embedded newlines
respectively, setting this flags is equivalent to prefixing the
expression with (?-m).
</p>
</td>
</tr>
<tr>
<td>
<p>
no_mod_s
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Normally whether Boost.Regex will match "." against
a newline character is determined by the match flag <code class="computeroutput"><span class="identifier">match_dot_not_newline</span></code>. Specifying
this flag is equivalent to prefixing the expression with <code class="computeroutput"><span class="special">(?-</span><span class="identifier">s</span><span class="special">)</span></code> and therefore causes "."
not to match a newline character regardless of whether <code class="computeroutput"><span class="identifier">match_not_dot_newline</span></code> is set
in the match flags.
</p>
</td>
</tr>
<tr>
<td>
<p>
mod_s
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Normally whether Boost.Regex will match "." against
a newline character is determined by the match flag <code class="computeroutput"><span class="identifier">match_dot_not_newline</span></code>. Specifying
this flag is equivalent to prefixing the expression with <code class="computeroutput"><span class="special">(?</span><span class="identifier">s</span><span class="special">)</span></code> and therefore causes "."
to match a newline character regardless of whether <code class="computeroutput"><span class="identifier">match_not_dot_newline</span></code> is set
in the match flags.
</p>
</td>
</tr>
<tr>
<td>
<p>
mod_x
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Turns on the perl x-modifier: causes unescaped whitespace in
the expression to be ignored.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_empty_expressions
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then empty expressions/alternatives are prohibited.
</p>
</td>
</tr>
<tr>
<td>
<p>
save_subexpression_location
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then the locations of individual sub-expressions within
the <span class="emphasis"><em>original regular expression string</em></span> can
be accessed via the <a class="link" href="../basic_regex.html#boost_regex.basic_regex.subexpression"><code class="computeroutput"><span class="identifier">subexpression</span><span class="special">()</span></code></a>
member function of <code class="computeroutput"><span class="identifier">basic_regex</span></code>.
</p>
</td>
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<td align="right"><div class="copyright-footer">Copyright © 1998 -2007 John Maddock<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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