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<title>Options for POSIX Basic Regular Expressions</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_regex.ref.syntax_option_type.syntax_option_type_basic"></a><a class="link" href="syntax_option_type_basic.html" title="Options for POSIX Basic Regular Expressions">
Options for POSIX Basic Regular Expressions</a>
</h4></div></div></div>
<p>
Exactly one of the following must always be set for POSIX basic 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>
basic
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that the grammar recognized by the regular expression
engine is the same as that used by <a class="link" href="../../syntax/basic_syntax.html" title="POSIX Basic Regular Expression Syntax">POSIX
basic regular expressions</a> in IEEE Std 1003.1-2001, Portable
Operating System Interface (POSIX ), Base Definitions and Headers,
Section 9, Regular Expressions (FWD.1).
</p>
</td>
</tr>
<tr>
<td>
<p>
sed
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
As Above.
</p>
</td>
</tr>
<tr>
<td>
<p>
grep
</p>
</td>
<td>
<p>
Yes
</p>
</td>
<td>
<p>
Specifies that the grammar recognized by the regular expression
engine is the same as that used by POSIX utility <code class="computeroutput"><span class="identifier">grep</span></code> in IEEE Std 1003.1-2001,
Portable Operating System Interface (POSIX ), Shells and Utilities,
Section 4, Utilit\ies, grep (FWD.1).
</p>
<p>
That is to say, the same as <a class="link" href="../../syntax/basic_syntax.html" title="POSIX Basic Regular Expression Syntax">POSIX
basic syntax</a>, but with the newline character acting as
an alternation character; the expression is treated as a newline
separated list of alternatives.
</p>
</td>
</tr>
<tr>
<td>
<p>
emacs
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
Specifies that the grammar recognised is the superset of the
<a class="link" href="../../syntax/basic_syntax.html" title="POSIX Basic Regular Expression Syntax">POSIX-Basic syntax</a>
used by the emacs program.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The following options may also be set when using POSIX basic 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. This bit is on by default for <a class="link" href="../../syntax/basic_syntax.html" title="POSIX Basic Regular Expression Syntax">POSIX-Basic regular
expressions</a>, but can be unset to force ranges to be compared
by code point only.
</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. This bit is already set, if you use the <code class="computeroutput"><span class="identifier">grep</span></code> option.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_char_classes
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then character classes such as <code class="computeroutput"><span class="special">[[:</span><span class="identifier">alnum</span><span class="special">:]]</span></code>
are not allowed.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_escape_in_lists
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set this makes the escape character ordinary inside lists,
so that <code class="computeroutput"><span class="special">[\</span><span class="identifier">b</span><span class="special">]</span></code> would match either '\' or 'b'.
This bit is on by default for <a class="link" href="../../syntax/basic_syntax.html" title="POSIX Basic Regular Expression Syntax">POSIX-basic
regular expressions</a>, but can be unset to force escapes
to be recognised inside lists.
</p>
</td>
</tr>
<tr>
<td>
<p>
no_intervals
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then bounded repeats such as a{2,3} are not permitted.
</p>
</td>
</tr>
<tr>
<td>
<p>
bk_plus_qm
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then <code class="computeroutput"><span class="special">\?</span></code>
acts as a zero-or-one repeat operator, and <code class="computeroutput"><span class="special">\+</span></code>
acts as a one-or-more repeat operator.
</p>
</td>
</tr>
<tr>
<td>
<p>
bk_vbar
</p>
</td>
<td>
<p>
No
</p>
</td>
<td>
<p>
When set then <code class="computeroutput"><span class="special">\|</span></code>
acts as the alternation operator.
</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>
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="left"></td>
<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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