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📄 [c++对象模型][9]虚继承与虚函数表 - itech's blog - 博客园.htm

📁 最为全面的c++内存模型探秘。不管是初学者还是老手
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style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestVT()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;B&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pB&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GD();<BR>&nbsp;&nbsp;&nbsp;&nbsp;GD&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pGD&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;dynamic_cast</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN style="COLOR: #000000">GD</SPAN><SPAN 
style="COLOR: #000000">*&gt;</SPAN><SPAN 
style="COLOR: #000000">(pB);<BR>&nbsp;&nbsp;&nbsp;&nbsp;pGD</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">i&nbsp;</SPAN><SPAN style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800080">10</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pGD</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">x&nbsp;</SPAN><SPAN style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800080">20</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pGD</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">y&nbsp;</SPAN><SPAN style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800080">30</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;pGD</SPAN><SPAN 
style="COLOR: #000000">-&gt;</SPAN><SPAN 
style="COLOR: #000000">a&nbsp;</SPAN><SPAN style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800080">40</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;PrintMemberAndVT(pGD);<BR>&nbsp;&nbsp;&nbsp;&nbsp;delete&nbsp;pGD;<BR>}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>6）验证代码结果：</P>
<P><IMG 
src="[C++对象模型][9]虚继承与虚函数表 - iTech's Blog - 博客园.files/2009022812593163.png"></P>
<P>&nbsp;</P>
<P>7）总结：</P>
<P><SPAN 
style="COLOR: #ff0000">虚继承，使公共的基类在子类中只有一份，我们看到虚继承在多重继承的基础上多了vbtable来存储到公共基类的偏移。</SPAN></P>
<P>&nbsp;</P>
<P>二 虚继承运行时类型转化 </P>
<P>&nbsp;</P>
<P>1）代码验证：<IMG id=Code_Closed_Image_130505 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_130505').style.display='none'; document.getElementById('Code_Open_Image_130505').style.display='inline'; document.getElementById('Code_Open_Text_130505').style.display='inline';" 
height=16 
src="[C++对象模型][9]虚继承与虚函数表 - iTech's Blog - 博客园.files/ContractedBlock.gif" 
width=11 align=top><SPAN id=Code_Open_Text_130505><SPAN 
style="COLOR: #000000"></SPAN></SPAN></P>
<P>&nbsp;</P>
<DIV class=cnblogs_code><IMG id=Code_Closed_Image_130736 style="DISPLAY: none" 
onclick="this.style.display='none'; document.getElementById('Code_Closed_Text_130736').style.display='none'; document.getElementById('Code_Open_Image_130736').style.display='inline'; document.getElementById('Code_Open_Text_130736').style.display='inline';" 
height=16 
src="[C++对象模型][9]虚继承与虚函数表 - iTech's Blog - 博客园.files/ContractedBlock.gif" 
width=11 align=top><IMG id=Code_Open_Image_130736 
onclick="this.style.display='none'; document.getElementById('Code_Open_Text_130736').style.display='none'; getElementById('Code_Closed_Image_130736').style.display='inline'; getElementById('Code_Closed_Text_130736').style.display='inline';" 
height=16 
src="[C++对象模型][9]虚继承与虚函数表 - iTech's Blog - 博客园.files/ExpandedBlockStart.gif" 
width=11 align=top><SPAN class=cnblogs_code_Collapse 
id=Code_Closed_Text_130736>Code</SPAN><SPAN id=Code_Open_Text_130736><BR><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><SPAN 
style="COLOR: #0000ff">void</SPAN><SPAN 
style="COLOR: #000000">&nbsp;TestDynamicCast()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;B&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN style="COLOR: #000000">pB&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;GD();<BR>&nbsp;&nbsp;&nbsp;&nbsp;GD&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pGD&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;dynamic_cast</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN style="COLOR: #000000">GD</SPAN><SPAN 
style="COLOR: #000000">*&gt;</SPAN><SPAN 
style="COLOR: #000000">(pB);<BR>&nbsp;&nbsp;&nbsp;&nbsp;cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">GD:</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pGD&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;D1&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pD1&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;dynamic_cast</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN style="COLOR: #000000">D1</SPAN><SPAN 
style="COLOR: #000000">*&gt;</SPAN><SPAN 
style="COLOR: #000000">(pB);<BR>&nbsp;&nbsp;&nbsp;&nbsp;cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">D1:</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pD1&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;D2&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">pD2&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;dynamic_cast</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN style="COLOR: #000000">D2</SPAN><SPAN 
style="COLOR: #000000">*&gt;</SPAN><SPAN 
style="COLOR: #000000">(pB);<BR>&nbsp;&nbsp;&nbsp;&nbsp;cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">D2:</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pD2&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;endl;<BR>&nbsp;&nbsp;&nbsp;&nbsp;cout&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #800000">B:</SPAN><SPAN style="COLOR: #800000">"</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;pB&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;endl;<BR>}</SPAN></SPAN></DIV>
<P>&nbsp;</P>
<P>&nbsp;</P>
<P>2）验证代码结果：</P>
<P><IMG 
src="[C++对象模型][9]虚继承与虚函数表 - iTech's Blog - 博客园.files/2009022813070883.png"></P>
<P>&nbsp;</P>
<P>3）总结：</P>
<P><SPAN 
style="COLOR: #ff0000">还是从内存布局来看dynamic_cast时地址的变化，第一个基类的地址与子类相同，其他的基类和虚基类需要做偏移。</SPAN></P>
<P>三 完！</P>
<DIV id=MySignature>
<P>感谢，Thanks！<BR><BR>作者：<A href="http://itech.cnblogs.com/">iTech</A><BR>出处：<A 
href="http://itech.cnblogs.com/">http://itech.cnblogs.com/</A> 
<BR>转载：本文版权归作者iTech所有，转载请注明出处，不得用于商业用途！</P></DIV>
<DIV id=EntryTag>Tag标签: <A 
href="http://www.cnblogs.com/itech/tag/[Cpp对象模型]/">[Cpp对象模型]</A></DIV></DIV>
<DIV class=postDesc>posted @ 2009-03-01 19:35 <A 
href="http://www.cnblogs.com/itech/">iTech</A> 阅读(49) <A 
href="http://www.cnblogs.com/itech/archive/2009/02/27/1399996.html#Post">评论(0)</A> 
&nbsp;<A 
href="http://www.cnblogs.com/itech/admin/EditPosts.aspx?postid=1399996">编辑</A> 
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onclick="PutInWz();return false;" 
href="http://www.cnblogs.com/itech/archive/2009/02/27/1399996.html#">网摘</A> 
所属分类: <A href="http://www.cnblogs.com/itech/category/170009.html">C++</A> 
</DIV></DIV><IMG height=1 
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