📄 c++的多态性实现机制剖析.htm
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<body lang=ZH-CN link=blue vlink=purple style='tab-interval:21.0pt;text-justify-trim:
punctuation'>
<div class=Section1 style='layout-grid:15.6pt'>
<p class=MsoNormal align=center style='text-align:center;line-height:150%;
mso-outline-level:1'><b style='mso-bidi-font-weight:normal'><span lang=EN-US
style='font-size:22.0pt;line-height:150%'>C++</span></b><b style='mso-bidi-font-weight:
normal'><span style='font-size:22.0pt;line-height:150%;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的多态性实现机制剖析</span></b><b
style='mso-bidi-font-weight:normal'><span lang=EN-US style='font-size:22.0pt;
line-height:150%'><o:p></o:p></span></b></p>
<p class=MsoNormal align=center style='text-align:center;line-height:150%;
mso-outline-level:1'><span style='font-size:15.0pt;line-height:150%;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>――即</span><span
lang=EN-US style='font-size:15.0pt;line-height:150%'>VC++</span><span
style='font-size:15.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>视频第三课</span><span
lang=EN-US style='font-size:15.0pt;line-height:150%'>this</span><span
style='font-size:15.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>指针详细说明</span><span
lang=EN-US style='font-size:15.0pt;line-height:150%'><o:p></o:p></span></p>
<p class=MsoNormal align=center style='text-align:center;line-height:150%;
mso-outline-level:1'><span style='font-size:12.0pt;line-height:150%;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>作者：孙鑫</span><span
style='font-size:12.0pt;line-height:150%'> </span><span style='font-size:12.0pt;
line-height:150%;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>时间：</span><st1:chsdate Year="2006"
Month="1" Day="12" IsLunarDate="False" IsROCDate="False" w:st="on"><span
lang=EN-US style='font-size:12.0pt;line-height:150%'>2006</span><span
style='font-size:12.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>年</span><span
lang=EN-US style='font-size:12.0pt;line-height:150%'>1</span><span
style='font-size:12.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>月</span><span
lang=EN-US style='font-size:12.0pt;line-height:150%'>12</span><span
style='font-size:12.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>日</span></st1:chsdate><span
style='font-size:12.0pt;line-height:150%;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>星期四</span><span
lang=EN-US style='font-size:12.0pt;line-height:150%'><o:p></o:p></span></p>
<h1 style='margin-left:21.25pt;text-indent:-21.25pt;mso-list:l0 level1 lfo1;
tab-stops:list 21.25pt'><![if !supportLists]><span lang=EN-US style='mso-fareast-font-family:
"Times New Roman"'><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>多态性和虚函数</span></h1>
<p class=MsoNormal style='line-height:150%'><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>我们先看一个例子：</span></p>
<div style='mso-element:para-border-div;border:none;border-bottom:solid windowtext 1.5pt;
padding:0cm 0cm 1.0pt 0cm'>
<p class=MsoCaption align=center style='text-align:center;border:none;
mso-border-bottom-alt:solid windowtext 1.5pt;padding:0cm;mso-padding-alt:0cm 0cm 1.0pt 0cm'><span
style='font-family:黑体;mso-ascii-font-family:Arial'>例</span><span lang=EN-US>1- </span><!--[if supportFields]><span
lang=EN-US><span style='mso-element:field-begin'></span><span
style='mso-spacerun:yes'> </span>SEQ </span><span style='font-family:黑体;
mso-ascii-font-family:Arial'>例</span><span lang=EN-US>1- \* ARABIC <span
style='mso-element:field-separator'></span></span><![endif]--><span lang=EN-US><span
style='mso-no-proof:yes'>1</span></span><!--[if supportFields]><span
lang=EN-US><span style='mso-element:field-end'></span></span><![endif]--></p>
</div>
<p class=MsoNormal><span lang=EN-US>#include <<span class=SpellE>iostream.h</span>></span></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>class</span></span><span
lang=EN-US> animal</span></p>
<p class=MsoNormal><span lang=EN-US>{</span></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>public</span></span><span
lang=EN-US>:</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span><span
class=GramE>void</span> sleep()</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span>{</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:2'> </span><span
class=SpellE><span class=GramE>cout</span></span><<"animal
sleep"<<<span class=SpellE>endl</span>;</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span>}</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span><span
class=GramE><b style='mso-bidi-font-weight:normal'>void</b></span><b
style='mso-bidi-font-weight:normal'> breathe()<o:p></o:p></b></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:1'> </span>{<o:p></o:p></span></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:2'> </span><span
class=SpellE><span class=GramE>cout</span></span><<"animal
breathe"<<<span class=SpellE>endl</span>;<o:p></o:p></span></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:1'> </span>}<o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN-US>};</span></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>class</span></span><span
lang=EN-US> <span class=SpellE>fish:public</span> animal</span></p>
<p class=MsoNormal><span lang=EN-US>{</span></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>public</span></span><span
lang=EN-US>:</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span><span
class=GramE><b style='mso-bidi-font-weight:normal'>void</b></span><b
style='mso-bidi-font-weight:normal'> breathe()<o:p></o:p></b></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:1'> </span>{<o:p></o:p></span></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:2'> </span><span
class=SpellE><span class=GramE>cout</span></span><<"fish
bubble"<<<span class=SpellE>endl</span>;<o:p></o:p></span></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:1'> </span>}<o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN-US>};</span></p>
<p class=MsoNormal><span class=GramE><span lang=EN-US>void</span></span><span
lang=EN-US> main()</span></p>
<p class=MsoNormal><span lang=EN-US>{</span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span><span
class=GramE><b style='mso-bidi-font-weight:normal'>fish</b></span><b
style='mso-bidi-font-weight:normal'> <span class=SpellE>fh</span>;<o:p></o:p></b></span></p>
<p class=MsoNormal><span lang=EN-US><span style='mso-tab-count:1'> </span><span
class=GramE><b style='mso-bidi-font-weight:normal'>animal</b></span><b
style='mso-bidi-font-weight:normal'> *<span class=SpellE>pAn</span>=&<span
class=SpellE>fh</span>;<o:p></o:p></b></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span lang=EN-US><span
style='mso-tab-count:1'> </span><span
class=SpellE><span class=GramE>pAn</span></span>->breathe();<o:p></o:p></span></b></p>
<div style='mso-element:para-border-div;border:none;border-bottom:solid windowtext 1.5pt;
padding:0cm 0cm 1.0pt 0cm'>
<p class=MsoNormal style='border:none;mso-border-bottom-alt:solid windowtext 1.5pt;
padding:0cm;mso-padding-alt:0cm 0cm 1.0pt 0cm'><span lang=EN-US>}</span></p>
</div>
<p class=MsoNormal style='line-height:150%'><span lang=EN-US><span
style='mso-tab-count:1'> </span></span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>注意，<span class=GramE>在例</span></span><span lang=EN-US>1-1</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的程序中没有定义虚函数。考虑<span class=GramE>一</span>下例</span><span
lang=EN-US>1-1</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>的程序执行的结果是什么？</span></p>
<p class=MsoNormal style='line-height:150%'><span lang=EN-US><span
style='mso-tab-count:1'> </span></span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>答案是输出：</span><span class=GramE><span lang=EN-US>animal</span></span><span
lang=EN-US> breathe</span></p>
<p class=MsoNormal style='line-height:150%'><span lang=EN-US><span
style='mso-tab-count:1'> </span></span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>我们在</span><span lang=EN-US>main()</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>函数中首先定义了一个</span><span lang=EN-US>fish</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>类的对象</span><span class=SpellE><span lang=EN-US>fh</span></span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
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