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26 | <div class="titlepage"><div><div><h3 class="title"> | |
27 | <a name="boost_typetraits.reference.is_virtual_base_of"></a><a class="link" href="is_virtual_base_of.html" title="is_virtual_base_of">is_virtual_base_of</a> | |
28 | </h3></div></div></div> | |
29 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Base</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Derived</span><span class="special">></span> | |
30 | <span class="keyword">struct</span> <span class="identifier">is_virtual_base_of</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span> | |
31 | </pre> | |
32 | <p> | |
33 | <span class="bold"><strong>Inherits:</strong></span> If Base is a virtual base class | |
34 | of type Derived then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, | |
35 | otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>. | |
36 | </p> | |
37 | <p> | |
38 | Types <code class="computeroutput"><span class="identifier">Base</span></code> and <code class="computeroutput"><span class="identifier">Derived</span></code> must not be incomplete types. | |
39 | </p> | |
40 | <p> | |
41 | <span class="bold"><strong>C++ Standard Reference:</strong></span> 10. | |
42 | </p> | |
43 | <p> | |
44 | <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span> | |
45 | <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_virtual_base_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> | |
46 | or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> | |
47 | </p> | |
48 | <p> | |
49 | <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers | |
50 | are supported by this trait. | |
51 | </p> | |
52 | <div class="note"><table border="0" summary="Note"> | |
53 | <tr> | |
54 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
55 | <th align="left">Note</th> | |
56 | </tr> | |
57 | <tr><td align="left" valign="top"><p> | |
58 | There are a small number of cases where it's simply not possible for this | |
59 | trait to work, and where attempting to instantiate the trait will cause | |
60 | compiler errors (see bug reports <a href="https://svn.boost.org/trac/boost/ticket/3730" target="_top">#3730</a> | |
61 | and <a href="https://svn.boost.org/trac/boost/ticket/11323" target="_top">11323</a>). | |
62 | Further more the issues may well be compiler specific. In this situation | |
63 | the user should supply a full specialization of the trait to work around | |
64 | the problem. | |
65 | </p></td></tr> | |
66 | </table></div> | |
67 | <p> | |
68 | <span class="bold"><strong>Examples:</strong></span> | |
69 | </p> | |
70 | <div class="blockquote"><blockquote class="blockquote"><p> | |
71 | Given: <code class="computeroutput"> <span class="keyword">class</span> <span class="identifier">Base</span><span class="special">{};</span> <span class="keyword">class</span> <span class="identifier">Derived</span> <span class="special">:</span> <span class="keyword">public</span> <span class="keyword">virtual</span> | |
72 | <span class="identifier">Base</span><span class="special">{};</span></code> | |
73 | </p></blockquote></div> | |
74 | <div class="blockquote"><blockquote class="blockquote"><p> | |
75 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">></span></code> | |
76 | inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. | |
77 | </p></blockquote></div> | |
78 | <div class="blockquote"><blockquote class="blockquote"><p> | |
79 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">>::</span><span class="identifier">type</span></code> is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. | |
80 | </p></blockquote></div> | |
81 | <div class="blockquote"><blockquote class="blockquote"><p> | |
82 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression | |
83 | that evaluates to <span class="emphasis"><em>true</em></span>. | |
84 | </p></blockquote></div> | |
85 | <div class="blockquote"><blockquote class="blockquote"><p> | |
86 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">SomeClassType</span><span class="special">,</span> | |
87 | <span class="identifier">SomeClassType</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression | |
88 | that evaluates to <span class="emphasis"><em>true</em></span>. | |
89 | </p></blockquote></div> | |
90 | <div class="blockquote"><blockquote class="blockquote"><p> | |
91 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">NotAClassType</span><span class="special">,</span> | |
92 | <span class="identifier">NotAClassType</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression | |
93 | that evaluates to <span class="emphasis"><em>false</em></span>. | |
94 | </p></blockquote></div> | |
95 | <div class="blockquote"><blockquote class="blockquote"><p> | |
96 | <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">value_type</span></code> | |
97 | is the type <code class="computeroutput"><span class="keyword">bool</span></code>. | |
98 | </p></blockquote></div> | |
99 | </div> | |
100 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
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107 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
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