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<title>例4-3</title>
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<blockquote>
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<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">#include
<iostream.h></font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">class
Time</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">Time(int
new_hours,int new_minutes)</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{</font></p>
<blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">hours=new_hours;</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">minutes=new_minutes;</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">int
get_hours( );</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
get_minutes( );</font></p>
</blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">protected:</font></p>
<blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
hours,minutes;</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">int
Time::get_hours( )</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{
return hours; }</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"> </p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
Time::get_minutes( )</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{
return minutes; }</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"> </p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">class
Timex:public Time</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">Timex(int
new_hours,int new_minutes,int new_seconds);</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
get_seconds( );</font></p>
</blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">protected:</font></p>
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<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
seconds;</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"> </p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">Timex::Timex(int
new_hours,int new_minutes,int new_seconds):Time(new_hours,new_minutes)</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">派生类构造函数后必须包括向基类传递参数的调用</font></font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{
seconds=new_seconds; }</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"> </p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">int
Timex::get_seconds( )</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{
return seconds; }</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"> </p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">void
main( )</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">{</font></p>
<blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">Time
time1(20,30);</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">Timex
time2(10,45,34);</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">cout<<time1.get_hours(
)<<":"<<time1.get_minutes( )<<endl;</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">cout<<time2.get_hours(
)<<":"<<time2.get_minutes(
)<<":"<<time2.get_seconds( )<<endl;</font></p>
</blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">}</font></p>
</blockquote>
</blockquote>
<font SIZE="3">
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">程序输出结果是：</font></p>
<blockquote>
<blockquote>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">20<font FACE="??ì?,SimSun" LANG="ZH-CN">：</font>30</font></p>
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"><font size="2">10<font FACE="??ì?,SimSun" LANG="ZH-CN">：</font>45<font FACE="??ì?,SimSun" LANG="ZH-CN">：</font>34</font></p>
</blockquote>
</blockquote>
<font SIZE="3">
<p ALIGN="justify" style="line-height: 100%; margin-top: 0; margin-bottom: 0"></font><font FACE="??ì?,SimSun" LANG="ZH-CN" size="2">说明：当基类定义有构造函数时，派生类必须定义构造函数，以提供将参数传递给基类构造函数的途径。因此在有些情况下，派生类的构造函数的函数体可能为空，仅起到参数传递的作用。</font></p>
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