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 <div class="section">
 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 <a name="id2536569"></a>Frequently Asked Questions</h2></div></div></div>
 <div class="qandaset">
 <a name="id2536576"></a><dl>
 <dt>1. <a href="s04.html#id2536578">Don't noncopyable signal semantics mean that a class
         with a signal member will be noncopyable as well?</a>
 </dt>
 <dt>2. <a href="s04.html#id2536601">Is Boost.Signals thread-safe?</a>
 </dt>
 <dt>3. <a href="s04.html#id2536622">How do I get Boost.Signals to work with Qt?</a>
 </dt>
 </dl>
 <table border="0" width="100%" summary="Q and A Set">
 <col align="left" width="1%">
 <col>
 <tbody>
 <tr class="question">
 <td align="left" valign="top">
 <a name="id2536578"></a><a name="id2536581"></a><p><b>1.</b></p>
 </td>
 <td align="left" valign="top"><p>Don't noncopyable signal semantics mean that a class
         with a signal member will be noncopyable as well?</p></td>
 </tr>
 <tr class="answer">
 <td align="left" valign="top"></td>
 <td align="left" valign="top"><p>No. The compiler will not be able to generate a copy
         constructor or copy assignment operator for your class if it
         has a signal as a member, but you are free to write your own
         copy constructor and/or copy assignment operator. Just don't
         try to copy the signal.</p></td>
 </tr>
 <tr class="question">
 <td align="left" valign="top">
 <a name="id2536601"></a><a name="id2536604"></a><p><b>2.</b></p>
 </td>
 <td align="left" valign="top"><p>Is Boost.Signals thread-safe?</p></td>
 </tr>
 <tr class="answer">
 <td align="left" valign="top"></td>
 <td align="left" valign="top"><p>No. Using Boost.Signals in a multithreaded concept is
         very dangerous, and it is very likely that the results will be
         less than satisfying. Boost.Signals will support thread safety
         in the future.</p></td>
 </tr>
 <tr class="question">
 <td align="left" valign="top">
 <a name="id2536622"></a><a name="id2536624"></a><p><b>3.</b></p>
 </td>
 <td align="left" valign="top"><p>How do I get Boost.Signals to work with Qt?</p></td>
 </tr>
 <tr class="answer">
 <td align="left" valign="top"></td>
 <td align="left" valign="top">
 <p>When building with Qt, the Moc keywords
         <code class="computeroutput">signals</code> and <code class="computeroutput">slots</code> are defined using
         preprocessor macros, causing programs using Boost.Signals and
         Qt together to fail to compile.</p>
 <p><span class="emphasis"><em>For Qt 4.1 and later</em></span>, This behavior
         can be turned off in Qt on a per-project or per-file basis
         with the <code class="computeroutput">no_keywords</code> option.  This works with
         out-of-the-box builds of Boost and Qt. You do not need to
         re-configure, re-build, or duplicate existing libraries. For a
         project where you want to use both Boost.Signals and Qt
         Signals and Slots, the relevant part of your .pro file might
         look like this:</p>
 <pre class="programlisting">
 CONFIG      += no_keywords # so Qt won't #define any non-all-caps `keywords'
 INCLUDEPATH += . /usr/local/include/boost-1_33_1/
 macx:LIBS   += /usr/local/lib/libboost_signals-1_33_1.a  # ...your exact paths may vary
 </pre>
 <p>Now you can mix Boost.Signals and Qt Signals and Slots
         in the same files, and even within the same class or function.
         You will have to use the upper-case versions of Qt macros in
         your own code.  See the article <a href="http://scottcollins.net/articles/a-deeper-look-at-signals-and-slots.html" target="_top">A
         Deeper Look at Signals and Slots</a> [off-site] for more
         complete examples and a survey of the strengths of the two
         systems.</p>
 <p><span class="emphasis"><em>Older versions of Qt</em></span> did not
         provide a reliable mechanism for avoiding these unfriendly,
         all lower-case `keyword'-like macros.  Although this is a
         problem with Qt and not Boost.Signals, a user can use the two
         systems together with a little extra effort. There are two
         ways to do this:</p>
 <p>The first way involves defining
         the <code class="computeroutput">BOOST_SIGNALS_NAMESPACE</code>
         macro to some other identifier (e.g., <code class="computeroutput">signalslib</code>)
         when building and using the Boost.Signals library. Then the
         namespace of the Boost.Signals library will be
         <code class="computeroutput">boost::BOOST_SIGNALS_NAMESPACE</code> instead of
         <code class="computeroutput">boost::signals</code>. To retain the original namespace
         name in translation units that do not interact with Qt, you
         can use a namespace alias:</p>
 <pre class="programlisting">
   namespace boost {
     namespace signals = BOOST_SIGNALS_NAMESPACE;
   }
 </pre>
 <p>The second way, provided by Frank Hess and improved by
         Niels Dekker, involves
         creating a header <code class="computeroutput">signalslib.hpp</code> that contains
           the following code:</p>
 <pre class="programlisting">#ifndef SIGNALSLIB_HPP_INCLUDED
 #define SIGNALSLIB_HPP_INCLUDED

 #if defined(signals) &amp;&amp; defined(QOBJECTDEFS_H) &amp;&amp; \
   !defined(QT_MOC_CPP)
 #  undef signals
 #  define signals signals
 #endif

 #include &lt;boost/signal.hpp&gt;
 namespace boost
 {
   namespace signalslib = signals;
 }

 #if defined(signals) &amp;&amp; defined(QOBJECTDEFS_H) &amp;&amp; \
   !defined(QT_MOC_CPP)
 #  undef signals
 // Restore the macro definition of "signals", as it was
 // defined by Qt's &lt;qobjectdefs.h&gt;.
 #  define signals protected
 #endif

 #endif</pre>
 <p>Use this header to include the Boost library, then refer
           to it in the namespace <code class="computeroutput">boost::signalslib</code>. This
           option is often
         preferable to the first option because it can be used without
         recompiling the Signals library binary. </p>
 </td>
 </tr>
 </tbody>
 </table>
 </div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 <td align="left"><p><small>Last revised: May 21, 2008 at 21:57:05 +0100</small></p></td>
 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2004 Douglas Gregor<p>Use, modification and distribution is subject to the Boost
     Software License, Version 1.0. (See accompanying file
     <code class="filename">LICENSE_1_0.txt</code> 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>
 </div></td>
 </tr></table>
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 <a accesskey="p" href="../boost/last_value_void_id625017.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../signals.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="s05.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
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	</div>
	<div class="section">
	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
	<a name="id2536569"></a>Frequently Asked Questions</h2></div></div></div>
	<div class="qandaset">
	<a name="id2536576"></a><dl>
	<dt>1. <a href="s04.html#id2536578">Don't noncopyable signal semantics mean that a class
	with a signal member will be noncopyable as well?</a>
	</dt>
	<dt>2. <a href="s04.html#id2536601">Is Boost.Signals thread-safe?</a>
	</dt>
	<dt>3. <a href="s04.html#id2536622">How do I get Boost.Signals to work with Qt?</a>
	</dt>
	</dl>
	<table border="0" width="100%" summary="Q and A Set">
	<col align="left" width="1%">
	<col>
	<tbody>
	<tr class="question">
	<td align="left" valign="top">
	<a name="id2536578"></a><a name="id2536581"></a><p><b>1.</b></p>
	</td>
	<td align="left" valign="top"><p>Don't noncopyable signal semantics mean that a class
	with a signal member will be noncopyable as well?</p></td>
	</tr>
	<tr class="answer">
	<td align="left" valign="top"></td>
	<td align="left" valign="top"><p>No. The compiler will not be able to generate a copy
	constructor or copy assignment operator for your class if it
	has a signal as a member, but you are free to write your own
	copy constructor and/or copy assignment operator. Just don't
	try to copy the signal.</p></td>
	</tr>
	<tr class="question">
	<td align="left" valign="top">
	<a name="id2536601"></a><a name="id2536604"></a><p><b>2.</b></p>
	</td>
	<td align="left" valign="top"><p>Is Boost.Signals thread-safe?</p></td>
	</tr>
	<tr class="answer">
	<td align="left" valign="top"></td>
	<td align="left" valign="top"><p>No. Using Boost.Signals in a multithreaded concept is
	very dangerous, and it is very likely that the results will be
	less than satisfying. Boost.Signals will support thread safety
	in the future.</p></td>
	</tr>
	<tr class="question">
	<td align="left" valign="top">
	<a name="id2536622"></a><a name="id2536624"></a><p><b>3.</b></p>
	</td>
	<td align="left" valign="top"><p>How do I get Boost.Signals to work with Qt?</p></td>
	</tr>
	<tr class="answer">
	<td align="left" valign="top"></td>
	<td align="left" valign="top">
	<p>When building with Qt, the Moc keywords
	<code class="computeroutput">signals</code> and <code class="computeroutput">slots</code> are defined using
	preprocessor macros, causing programs using Boost.Signals and
	Qt together to fail to compile.</p>
	<p><span class="emphasis"><em>For Qt 4.1 and later</em></span>, This behavior
	can be turned off in Qt on a per-project or per-file basis
	with the <code class="computeroutput">no_keywords</code> option. This works with
	out-of-the-box builds of Boost and Qt. You do not need to
	re-configure, re-build, or duplicate existing libraries. For a
	project where you want to use both Boost.Signals and Qt
	Signals and Slots, the relevant part of your .pro file might
	look like this:</p>
	<pre class="programlisting">
	CONFIG += no_keywords # so Qt won't #define any non-all-caps `keywords'
	INCLUDEPATH += . /usr/local/include/boost-1_33_1/
	macx:LIBS += /usr/local/lib/libboost_signals-1_33_1.a # ...your exact paths may vary
	</pre>
	<p>Now you can mix Boost.Signals and Qt Signals and Slots
	in the same files, and even within the same class or function.
	You will have to use the upper-case versions of Qt macros in
	your own code. See the article <a href="http://scottcollins.net/articles/a-deeper-look-at-signals-and-slots.html" target="_top">A
	Deeper Look at Signals and Slots</a> [off-site] for more
	complete examples and a survey of the strengths of the two
	systems.</p>
	<p><span class="emphasis"><em>Older versions of Qt</em></span> did not
	provide a reliable mechanism for avoiding these unfriendly,
	all lower-case `keyword'-like macros. Although this is a
	problem with Qt and not Boost.Signals, a user can use the two
	systems together with a little extra effort. There are two
	ways to do this:</p>
	<p>The first way involves defining
	the <code class="computeroutput">BOOST_SIGNALS_NAMESPACE</code>
	macro to some other identifier (e.g., <code class="computeroutput">signalslib</code>)
	when building and using the Boost.Signals library. Then the
	namespace of the Boost.Signals library will be
	<code class="computeroutput">boost::BOOST_SIGNALS_NAMESPACE</code> instead of
	<code class="computeroutput">boost::signals</code>. To retain the original namespace
	name in translation units that do not interact with Qt, you
	can use a namespace alias:</p>
	<pre class="programlisting">
	namespace boost {
	namespace signals = BOOST_SIGNALS_NAMESPACE;
	}
	</pre>
	<p>The second way, provided by Frank Hess and improved by
	Niels Dekker, involves
	creating a header <code class="computeroutput">signalslib.hpp</code> that contains
	the following code:</p>
	<pre class="programlisting">#ifndef SIGNALSLIB_HPP_INCLUDED
	#define SIGNALSLIB_HPP_INCLUDED

	#if defined(signals) && defined(QOBJECTDEFS_H) && \
	!defined(QT_MOC_CPP)
	# undef signals
	# define signals signals
	#endif

	#include <boost/signal.hpp>
	namespace boost
	{
	namespace signalslib = signals;
	}

	#if defined(signals) && defined(QOBJECTDEFS_H) && \
	!defined(QT_MOC_CPP)
	# undef signals
	// Restore the macro definition of "signals", as it was
	// defined by Qt's <qobjectdefs.h>.
	# define signals protected
	#endif

	#endif</pre>
	<p>Use this header to include the Boost library, then refer
	to it in the namespace <code class="computeroutput">boost::signalslib</code>. This
	option is often
	preferable to the first option because it can be used without
	recompiling the Signals library binary. </p>
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	</div>
	<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
	<td align="left"><p><small>Last revised: May 21, 2008 at 21:57:05 +0100</small></p></td>
	<td align="right"><div class="copyright-footer">Copyright © 2001-2004 Douglas Gregor<p>Use, modification and distribution is subject to the Boost
	Software License, Version 1.0. (See accompanying file
	<code class="filename">LICENSE_1_0.txt</code> 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>
	</div></td>
	</tr></table>
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