item_019.htm

C++程序编写规范,适合C++中级读者

<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"'>示例</span></b></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><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"'>示例</span><span lang=EN-US>1</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"'>：用缺省的初始值或</span> <span lang=EN-US>?: </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"'>来降低数据流和控制流的混杂度。</span></i></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </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"'>不推荐：没有初始化变量</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span lang=EN-US style='font-family:"Arial Black"'>int
speedupFactor;<o:p></o:p></span></p>

<p class=MsoNormal><span lang=EN-US>if( condition )</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span>speedupFactor = 2;</span></p>

<p class=MsoNormal><span lang=EN-US>else</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span>speedupFactor = -1;</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </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"'>较好：初始化了变量</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span lang=EN-US>int speedupFactor </span><span lang=EN-US
style='font-family:"Arial Black"'>= -1;</span></p>

<p class=MsoNormal><span lang=EN-US>if( condition )</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span>speedupFactor = 2;</span></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </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"'>较好：初始化了变量</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span lang=EN-US>int speedupFactor </span><span lang=EN-US
style='font-family:"Arial Black"'>= condition ? 2 : -1;</span></p>

<p class=MsoNormal><span lang=EN-US style='color:red'><o:p>&nbsp;</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"'>这些较好的替代方式没有在变量的定义和初始化之间留下任何空隙，这很好。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><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"'>示例</span><span lang=EN-US>2</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"'>：用一个函数代替复杂的计算过程</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。有时一个值是通过计算得到的，这时最好把计算的过程封装到一个函数中（参见第</span><span
lang=EN-US>11</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>&nbsp;</o:p></span></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </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"'>不推荐：没有初始化变量</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span lang=EN-US style='font-family:"Arial Black"'>int
speedupFactor;<o:p></o:p></span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span lang=EN-US>if( condition ) {</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span><i style='mso-bidi-font-style:
normal'>// … code …<o:p></o:p></i></span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span>speedupFactor =
someValue;</span></p>

<p class=MsoNormal><span lang=EN-US>}else {</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span><i style='mso-bidi-font-style:
normal'>// … code …<o:p></o:p></i></span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span>speedupFactor =
someOtherValue;</span></p>

<p class=MsoNormal><span lang=EN-US>}</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// </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"'>较好：初始化了变量</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal style='tab-stops:246.5pt'><span lang=EN-US>int speedupFactor
= </span><span lang=EN-US style='font-family:"Arial Black"'>ComputeSpeedupFactor();</span></p>

<p class=MsoNormal><span lang=EN-US style='color:red'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><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"'>示例</span><span lang=EN-US>3</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"'>：数组的初始化</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。对于较大的聚合类型如数组，适当的初始化并不意味着一定要触及（</span><span lang=EN-US>touch</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>）所有的数据。例如，如果你要使用一个</span><span lang=EN-US>API</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>，而该</span><span lang=EN-US>API</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>必须使用长度为</span><span
lang=EN-US>MAX_PATH</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的</span><span
lang=EN-US>char</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>类型的定长数组（但是请参见第</span><span lang=EN-US>77</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>和</span><span lang=EN-US>78</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>条）。如果你确信数组是以</span><span
lang=EN-US>null</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>结尾的</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"'>风格的字符串，那么这样的赋值就足够了：</span></p>

<p class=MsoNormal style='margin-left:36.0pt'><i style='mso-bidi-font-style:
normal'><span lang=EN-US>// </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"'>可以接受</span><span lang=EN-US>: </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"'>创建一个空的路径</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US>char
path[MAX_PATH]; path[0] = ‘\0’;</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>下面的初始化更安全，它把数组中所有的字符都设为零：</span></p>

<p class=MsoNormal style='margin-left:36.0pt'><i style='mso-bidi-font-style:
normal'><span lang=EN-US>// </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"'>更好：创建一个全部填零的路径</span></i></p>

<p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US>char
path[MAX_PATH] = { ‘\0’ };</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>以上两种初始化方法我们都推荐，但一般来说应该首选安全性而不是不必要的效率。</span></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>例外</span></b></p>

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</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"'>程序无需初始化由硬件或其它进程直接写入的输入缓冲区和</span><span
lang=EN-US>volatile</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>数据。</span></p>

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