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<div class=Section1>
<h3><span lang=EN-US>95. </span><span style='font-family:宋体;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial'>不要用</span><span lang=EN-US>C</span><span
style='font-family:宋体;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial'>风格的强制类型转换。</span></h3>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>摘要</span><span lang=EN-US><o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>年龄和智慧并不一定成正比：</span><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"'>风格的强制类型转换在不同的上下文中具有不同的（经常是危险的）语义，所有这些都隐藏在相同的语法背后。用</span><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"'>风格的强制类型转换代替</span><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"'>风格的类型转换有助于预防意想不到的错误。</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>讨论</span><span lang=EN-US><o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><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"'>风格的强制类型转换的一个问题在于用相同的语法做不完全相同的事情，依赖于这些变幻莫测的行为就像是依赖于</span><span
lang=EN-US>#include</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的文件一样。而</span><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"'>风格的类型转换，虽然仍保留了强制类型转换本质上存在的危险性，但是它避免了</span><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"'>风格的类型转换存在的多义性，并清晰地说明了意图，容易搜寻，写起来更费时间（这就使人在写之前要三思），也不会悄悄地插入有害的</span><span
class=SpellE><span lang=EN-US>reinterpret_cast</span></span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>（参见第</span><span lang=EN-US>92</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>条）。</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>考虑以下代码，</span><span lang=EN-US>Derived</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>从</span><span lang=EN-US>Base</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>继承而来：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal style='margin-left:36.0pt'><span class=GramE><span
lang=EN-US>extern</span></span><span lang=EN-US> void Fun( Derived* );</span></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal style='margin-left:36.0pt'><span class=GramE><span
lang=EN-US>void</span></span><span lang=EN-US> Gun( Base* <span class=SpellE>pb</span>
) {</span></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><i style='mso-bidi-font-style:
normal'>// </i></span><i style='mso-bidi-font-style:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>让我们假设</span><span lang=EN-US>Gun</span></i><i
style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>清楚地知道</span><span
class=SpellE><span lang=EN-US>pb</span></span></i><i style='mso-bidi-font-style:
normal'><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>实际指向</span><span lang=EN-US>Derived<o:p></o:p></span></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><i style='mso-bidi-font-style:
normal'>// </i></span><i style='mso-bidi-font-style:normal'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>并要把它传给</span><span lang=EN-US>Fun<o:p></o:p></span></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span>Derived* pd = (Base*)<span
class=SpellE>pb</span>;<span style='mso-tab-count:1'> </span><span
style='mso-tab-count:1'> </span><i
style='mso-bidi-font-style:normal'>// </i></span><i style='mso-bidi-font-style:
normal'><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>糟糕：</span><span lang=EN-US>C</span></i><i
style='mso-bidi-font-style:normal'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>风格的强制类型转换</span></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US><span
style='mso-spacerun:yes'> </span><span
style='mso-spacerun:yes'> </span><span class=GramE>Fun(</span> pd );</span></p>
<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US>}</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>如果</span><span lang=EN-US>Gun</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
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