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<span style="background-color: #CCFF99">第 7 章</span><span style="background-color: #CCFF99">
</span>><span style="background-color: #CCFF99"> 第 4 节 </span>><span style="background-color: #CCFF99">
7.4 </span><span style="background-color: #CCFF99">用户自定义类型的输入输出</span></p>
<hr color="#008000" size="1">
<p class="MsoNormal" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><span lang="EN-US">C++</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">语言的</span><span lang="EN-US">I/O</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">流库的一个很重要的特性是能够支持新的数据类型——用户自定义类型的输入和输出。实现这种功能的方式是重载插入操作符</span><span lang="EN-US"><<</span><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">和提取操作符</span><span lang="EN-US">>></span><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">。</span></font></p>
<p class="MsoNormal" style="line-height: 100%; margin-top: 0; margin-bottom: 0"> </p>
<p class="a0" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">【例</span><span lang="EN-US">7-9</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">】重载插入运算符。</span></font></p>
<blockquote>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">#include
<iomanip.h></font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><span lang="EN-US">class
RMB<span style="mso-spacerun:
yes">
</span>//</span><span style="font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">声明</span><span lang="EN-US">RMB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">类</span></font></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">public:</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">RMB(double v=0.0)</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">yuan=unsigned(v);</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">jf=unsigned((v-yuan)*100.0+0.5);</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">}</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">operator double( )</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">return yuan+jf/100.0;</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">}</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">void display(ostream& out)</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">out<<yuan<<'.'<<setfill('0')</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2"><<setw(2)<<jf<<setfill(' ');</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">}</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">protected:</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">unsigned int yuan;</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">unsigned int jf;</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">};</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><span lang="EN-US">ostream&
operator << (ostream& ot,RMB& d)<span style="mso-spacerun: yes">
</span>//</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">重载插入符</span><span lang="EN-US"><<</span></font></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">d.display(ot);</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">return ot;</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">}</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">void
main( )</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">{</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">RMB rmb(1.5);</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">cout<<"Initially
rmb="<<rmb<<"\n";</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">rmb=2.0*rmb;</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><span style="mso-tab-count:1"><font size="2">
</font></span><font size="2">cout<<"then
rmb="<<rmb<<"\n";</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">}</font></span></p>
<p class="MsoNormal" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span style="mso-spacerun: yes" lang="EN-US"><font size="2"> </font></span></p>
</blockquote>
<p class="MsoNormal" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2"><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">程序运行结果是：</span></font></p>
<blockquote>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">Initially
rmb=1.50</font></span></p>
<p class="a" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><span lang="EN-US"><font size="2">Then
rmb=3.00</font></span></p>
</blockquote>
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