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<title>第 4 章</title>
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<p style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span style="position: absolute; left: 4; top: -8"><font size="2"><img border="0" src="1.gif" width="63" height="70"></font></span></p>
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<span style="background-color: #CCFF99">第 4 章 </span>><span style="background-color: #CCFF99"> 第
2 节 </span>><span style="background-color: #CCFF99">
4.2 多重继承</span></font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0" class="右标题"><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">多重继承可以看作是单继承的扩展。所谓多重继承是指派生类具有多个基类，派生类与每个基类之间的关系仍可看作是一个单继承。</font></p>
<p ALIGN="justify" style="line-height: 200%; margin-top: 0; margin-bottom: 0"><font FACE="oúì?,SimHei" LANG="ZH-CN" size="2">1.
多重继承的定义</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">多重继承下派生类的定义格式如下：</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000">class
<font FACE="??ì?,SimSun" LANG="ZH-CN">派生类名</font>: <font FACE="??ì?,SimSun" LANG="ZH-CN">继承方式</font>1
<font FACE="??ì?,SimSun" LANG="ZH-CN">基类名</font>1, <font FACE="??ì?,SimSun" LANG="ZH-CN">继承方式</font>2
<font FACE="??ì?,SimSun" LANG="ZH-CN">基类名</font>2, <font FACE="??ì?,SimSun" LANG="ZH-CN">…</font></font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000">{</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000"><font FACE="??ì?,SimSun" LANG="ZH-CN">派生类类体</font>;</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000">};</font></p>
</blockquote>
</blockquote>
<p ALIGN="justify" style="line-height: 200%; margin-top: 0; margin-bottom: 0"><font FACE="oúì?,SimHei" LANG="ZH-CN" size="2">2.
多重继承的构造函数</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">在多继承的情况下，派生类的构造函数格式如下：</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000"><font FACE="??ì?,SimSun" LANG="ZH-CN">派生类名</font>(<font FACE="??ì?,SimSun" LANG="ZH-CN">总参数表</font>):
<font FACE="??ì?,SimSun" LANG="ZH-CN">基类名</font>1(<font FACE="??ì?,SimSun" LANG="ZH-CN">参数表</font>1),
<font FACE="??ì?,SimSun" LANG="ZH-CN">基类名</font>2(<font FACE="??ì?,SimSun" LANG="ZH-CN">参数表</font>2),
<font FACE="??ì?,SimSun" LANG="ZH-CN">…</font>,<font FACE="??ì?,SimSun" LANG="ZH-CN">子对象名</font>(<font FACE="??ì?,SimSun" LANG="ZH-CN">参数表</font>n+1),
<font FACE="??ì?,SimSun" LANG="ZH-CN">…</font></font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000">{</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000"><font FACE="??ì?,SimSun" LANG="ZH-CN">派生类构造函数体</font>;</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2" color="#008000">}</font></p>
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<p style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2" color="#008000">其中，“总参数表”中各个参数包含了其后的各个分参数表。</font></p>
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<p style="line-height: 100%; text-indent: 0; margin: 0" align="left"><font size="2"><font FACE="??ì?,SimSun" LANG="ZH-CN"><a href="example4-4.htm" target="_blank">【例</a></font><a href="example4-4.htm" target="_blank">4-4<font FACE="??ì?,SimSun" LANG="ZH-CN">】</font></a><font FACE="??ì?,SimSun" LANG="ZH-CN">派生类构造函数的构成及其执行顺序。</font></font></p>
<p ALIGN="justify" style="line-height: 200%; margin-top: 0; margin-bottom: 0"><font FACE="oúì?,SimHei" LANG="ZH-CN" size="2">3.
二义性问题</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">一般说来，在派生类中对基类成员的访问应该是唯一的，但是，由于多继承情况下，可能造成对基类中某成员的访问出现不唯一的情况，这称为对基类成员访问的二义性问题。</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 10; margin-bottom: 0"><font FACE="??ì?,SimSun" LANG="ZH-CN" SIZE="3"><font size="2">①</font>
</font><font size="2">情况1：</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><font FACE="??ì?,SimSun" LANG="ZH-CN">【例</font>4-5<font FACE="??ì?,SimSun" LANG="ZH-CN">】二义性问题。</font></font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">class
A</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">public:</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
f( );</font></p>
</blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">};</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">class
B</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">public:</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
f( );</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
g( );</font></p>
</blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">};</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">class
C : public A, public B</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">public:</font></p>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
g( );</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
h( );</font></p>
</blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">};</font></p>
</blockquote>
</blockquote>
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<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font size="2"><font FACE="??ì?,SimSun" LANG="ZH-CN">如果定义一个类</font>C<font FACE="??ì?,SimSun" LANG="ZH-CN">的对象</font>c1<font FACE="??ì?,SimSun" LANG="ZH-CN">，则对函数</font>f(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">的访问便具有二义性：</font></font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.f(
);</font></p>
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</blockquote>
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