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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">是访问类</font>A<font FACE="??ì?,SimSun" LANG="ZH-CN">中的</font>f(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">，还是访问类</font>B<font FACE="??ì?,SimSun" LANG="ZH-CN">中的</font>f(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">呢？</font></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">解决的方法可用前面用过的成员名限定法来消除二义性，例如：</font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.<font color="#FF6600">A::</font>f(
);</font></p>
</blockquote>
</blockquote>
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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">或者</font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.<font color="#FF6600">B::</font>f(
);</font></p>
</blockquote>
</blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font FACE="??ì?,SimSun" LANG="ZH-CN" SIZE="3"><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">②</font><font face="??ì?,SimSun">
</font></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">情况2：</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">在前例中，类</font>B<font FACE="??ì?,SimSun" LANG="ZH-CN">中有一个成员函数</font>g(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">，类</font>C<font FACE="??ì?,SimSun" LANG="ZH-CN">中也有一个成员函数</font>g(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">。这时，</font></font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.g(
);</font></p>
</blockquote>
</blockquote>
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<p style="line-height: 120%; margin-top: 0; margin-bottom: 0"></font><font size="2"><font FACE="??ì?,SimSun" LANG="ZH-CN">不存在二义性，它是指</font>C::g(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">，而不是指</font>B::g( )<font FACE="??ì?,SimSun" LANG="ZH-CN">。因为这两个</font>g(
)<font FACE="??ì?,SimSun" LANG="ZH-CN">函数，一个出现在基类</font>B<font FACE="??ì?,SimSun" LANG="ZH-CN">中，一个出现在派生类</font>C<font FACE="??ì?,SimSun" LANG="ZH-CN">中。在类的派生层次结构中，基类的成员和派生类新增的成员的作用范围不同，是相互包含的两个层，派生类在内层。</font></font></p>
<p style="line-height: 120%; margin-top: 0; margin-bottom: 0"><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2"><font color="#FF6600">对于在不同的作用域声明的标识符，可见性原则是：</font>如果存在两个或多个具有包含关系的作用域，外层声明的标识符如果在内层没有声明同名标识符，那么它在内层仍可见；如果内层声明了同名标识符，则外层标识符在内层不可见，这时称内层变量覆盖了外层同名变量，这种现象称为<font color="#FF6600">同名覆盖</font>。</font></p>
<p style="line-height: 100%; margin-top: 10; margin-bottom: 0"><font FACE="??ì?,SimSun" LANG="ZH-CN" SIZE="3"><font face="??ì?,SimSun" lang="ZH-CN" size="2">③</font><font face="??ì?,SimSun">
</font></font><font face="??ì?,SimSun" lang="ZH-CN" size="2">情况3：</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">当一个派生类从多个基类派生，而这些基类又有一个共同的基类，则对该基类中说明的成员进行访问时，也可能会出现二义性。例如：</font></p>
<blockquote>
<blockquote>
<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>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
a;</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
B1 : public 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">private:</font></p>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
b1;</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
B2 : public 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">private:</font></p>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
b2;</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 B1, public B2</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>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
f( );</font></p>
</blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">private:</font></p>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
c;</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 FACE="??ì?,SimSun" LANG="ZH-CN" size="2">已知：</font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">C
c1;</font></p>
</blockquote>
</blockquote>
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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">下面的两个访问都有二义性：</font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.a;</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.A::a;</font></p>
</blockquote>
</blockquote>
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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">而下面的访问是正确的：</font></p>
<blockquote>
<blockquote>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.B1::a;</font></p>
<p ALIGN="JUSTIFY" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">c1.B2::a;</font></p>
</blockquote>
</blockquote>
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