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| 26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
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| 27 | <a name="id1633680"></a>Frequently Asked Questions</h2></div></div></div> |
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| 28 | <div class="qandaset"> |
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| 29 | <dl> |
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| 30 | <dt>1. <a href="s04.html#id1633688">Don't noncopyable signal semantics mean that a class |
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| 31 | with a signal member will be noncopyable as well?</a> |
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| 32 | </dt> |
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| 33 | <dt>2. <a href="s04.html#id1633711">Is Boost.Signals thread-safe?</a> |
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| 34 | </dt> |
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| 35 | <dt>3. <a href="s04.html#id1633734">How do I get Boost.Signals to work with Qt?</a> |
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| 36 | </dt> |
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| 37 | </dl> |
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| 38 | <table border="0" summary="Q and A Set"> |
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| 39 | <col align="left" width="1%"> |
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| 40 | <tbody> |
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| 41 | <tr class="question"> |
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| 42 | <td align="left" valign="top"> |
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| 43 | <a name="id1633688"></a><a name="id1633690"></a><b>1.</b> |
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| 44 | </td> |
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| 45 | <td align="left" valign="top"><p>Don't noncopyable signal semantics mean that a class |
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| 46 | with a signal member will be noncopyable as well?</p></td> |
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| 47 | </tr> |
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| 48 | <tr class="answer"> |
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| 49 | <td align="left" valign="top"><b></b></td> |
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| 50 | <td align="left" valign="top"><p>No. The compiler will not be able to generate a copy |
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| 51 | constructor or copy assignment operator for your class if it |
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| 52 | has a signal as a member, but you are free to write your own |
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| 53 | copy constructor and/or copy assignment operator. Just don't |
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| 54 | try to copy the signal.</p></td> |
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| 55 | </tr> |
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| 56 | <tr class="question"> |
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| 57 | <td align="left" valign="top"> |
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| 58 | <a name="id1633711"></a><a name="id1633713"></a><b>2.</b> |
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| 59 | </td> |
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| 60 | <td align="left" valign="top"><p>Is Boost.Signals thread-safe?</p></td> |
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| 61 | </tr> |
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| 62 | <tr class="answer"> |
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| 63 | <td align="left" valign="top"><b></b></td> |
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| 64 | <td align="left" valign="top"><p>No. Using Boost.Signals in a multithreaded concept is |
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| 65 | very dangerous, and it is very likely that the results will be |
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| 66 | less than satisfying. Even trying to invoke the same signal from |
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| 67 | two different threads is dangerous. Although we would like to |
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| 68 | make Signals thread-safe, it is unlikely to happen without |
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| 69 | help from other developers.</p></td> |
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| 70 | </tr> |
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| 71 | <tr class="question"> |
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| 72 | <td align="left" valign="top"> |
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| 73 | <a name="id1633734"></a><a name="id1633736"></a><b>3.</b> |
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| 74 | </td> |
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| 75 | <td align="left" valign="top"><p>How do I get Boost.Signals to work with Qt?</p></td> |
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| 76 | </tr> |
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| 77 | <tr class="answer"> |
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| 78 | <td align="left" valign="top"><b></b></td> |
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| 79 | <td align="left" valign="top"> |
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| 80 | <p>When building with Qt, the Moc keywords |
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| 81 | <code class="computeroutput">signals</code> and <code class="computeroutput">slots</code> are defined using |
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| 82 | preprocessor macros, causing programs using Boost.Signals and |
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| 83 | Qt together to fail to compile.</p> |
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| 84 | <p><span class="emphasis"><em>For Qt 4.1 and later</em></span>, This behavior |
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| 85 | can be turned off in Qt on a per-project or per-file basis |
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| 86 | with the <code class="computeroutput">no_keywords</code> option. This works with |
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| 87 | out-of-the-box builds of Boost and Qt. You do not need to |
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| 88 | re-configure, re-build, or duplicate existing libraries. For a |
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| 89 | project where you want to use both Boost.Signals and Qt |
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| 90 | Signals and Slots, the relevant part of your .pro file might |
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| 91 | look like this:</p> |
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| 92 | <pre class="programlisting"> |
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| 93 | CONFIG += no_keywords # so Qt won't #define any non-all-caps `keywords' |
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| 94 | INCLUDEPATH += . /usr/local/include/boost-1_33_1/ |
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| 95 | macx:LIBS += /usr/local/lib/libboost_signals-1_33_1.a # ...your exact paths may vary |
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| 96 | </pre> |
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| 97 | <p>Now you can mix Boost.Signals and Qt Signals and Slots |
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| 98 | in the same files, and even within the same class or function. |
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| 99 | You will have to use the upper-case versions of Qt macros in |
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| 100 | your own code. See the article <a href="http://scottcollins.net/articles/a-deeper-look-at-signals-and-slots.html" target="_top">A |
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| 101 | Deeper Look at Signals and Slots</a> [off-site] for more |
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| 102 | complete examples and a survey of the strengths of the two |
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| 103 | systems.</p> |
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| 104 | <p><span class="emphasis"><em>Older versions of Qt</em></span> did not |
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| 105 | provide a reliable mechanism for avoiding these unfriendly, |
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| 106 | all lower-case `keyword'-like macros. Although this is a |
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| 107 | problem with Qt and not Boost.Signals, a user can use the two |
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| 108 | systems together with a little extra effort. There are two |
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| 109 | ways to do this:</p> |
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| 110 | <p>The first way involves defining |
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| 111 | the <code class="computeroutput">BOOST_SIGNALS_NAMESPACE</code> |
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| 112 | macro to some other identifier (e.g., <code class="computeroutput">signalslib</code>) |
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| 113 | when building and using the Boost.Signals library. Then the |
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| 114 | namespace of the Boost.Signals library will be |
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| 115 | <code class="computeroutput">boost::BOOST_SIGNALS_NAMESPACE</code> instead of |
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| 116 | <code class="computeroutput">boost::signals</code>. To retain the original namespace |
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| 117 | name in translation units that do not interact with Qt, you |
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| 118 | can use a namespace alias:</p> |
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| 119 | <pre class="programlisting"> |
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| 120 | namespace boost { |
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| 121 | namespace signals = BOOST_SIGNALS_NAMESPACE; |
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| 122 | } |
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| 123 | </pre> |
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| 124 | <p>The second way, provided by Frank Hess, involves |
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| 125 | creating a header <code class="computeroutput">signalslib.hpp</code> that contains |
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| 126 | the following code:</p> |
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| 127 | <pre class="programlisting">#ifdef signals |
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| 128 | #error "signalslib.hpp must be included before any qt header" |
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| 129 | #endif |
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| 130 | |
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| 131 | #include <boost/signal.hpp> |
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| 132 | namespace boost |
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| 133 | { |
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| 134 | namespace signalslib = signals; |
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| 135 | }</pre> |
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| 136 | <p>This header must be included before any Qt headers. Once |
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| 137 | it has been included, you can refer to the Signals library via |
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| 138 | the namespace <code class="computeroutput">boost::signalslib</code>. This option is |
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| 139 | preferable to the first option because it can be used without |
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| 140 | recompiling the Signals library binary. </p> |
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| 141 | </td> |
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| 142 | </tr> |
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| 143 | </tbody> |
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| 144 | </table> |
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| 145 | </div> |
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| 146 | </div> |
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| 147 | <table width="100%"><tr> |
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| 148 | <td align="left"><small><p>Last revised: November 03, 2006 at 19:45:40 GMT</p></small></td> |
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| 149 | <td align="right"><small>Copyright © 2001-2004 Douglas Gregor</small></td> |
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| 150 | </tr></table> |
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