item_001.htm

C++程序编写规范,适合C++中级读者

"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"'>：一个第三方的头文件</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。一个你无法修改的头文件可能包含会产生警告（可能是良性的）的代码。如果是这样的话，那么就用自己的版本把该头文件封装起来，在自己的版本中</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"'>原来的头文件，并仅在该作用域中有选择地关闭那些干扰性的警告，然后在整个项目的其余部分</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"'>封装后的头文件。例如（注意用来控制警告的语法根据编译器的不同而不同）：</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"'>文件：</span><span
lang=EN-US> <span class=SpellE>myproj/my_lambda.h</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"'>——</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"'>封装了</span><span
lang=EN-US>Boost</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"'>中的</span><span class=SpellE><span lang=EN-US>lambda.hpp</span></span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>//<span
style='mso-spacerun:yes'>&nbsp; </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"'>始终包含此文件，不要直接使用</span><span
class=SpellE><span lang=EN-US>lambda.hpp</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"'>。</span><span lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>//<span
style='mso-spacerun:yes'>&nbsp; </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"'>注意：我们的构建现在会自动检查</span> <span
lang=EN-US>&quot;<span class=SpellE>grep</span> <span class=SpellE>lambda.hpp</span>
&lt;<span class=SpellE>srcfile</span>&gt;&quot;</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"'>。</span><span lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>// <span
class=SpellE>Boost.Lambda</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"'>会产生无用的编译器警告，这些警告是无害的。</span><span lang=EN-US><o:p></o:p></span></i></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"'>一旦</span><span
class=SpellE><span lang=EN-US>Boost.Lambda</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"'>修正了这个问题，我们将删除下面的</span><span
class=SpellE><span lang=EN-US>pragma</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"'>，</span><span lang=EN-US><o:p></o:p></span></i></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"'>但是此头文件仍会存在。</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>//<o:p></o:p></span></i></p>

<p class=MsoNormal><span lang=EN-US>#<span class=SpellE>pragma</span> warning(push)<span
style='mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp; </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"'>仅在此头文件中禁用</span></i></p>

<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'>&nbsp;</span><span
style='mso-spacerun:yes'>&nbsp;</span><span style='mso-spacerun:yes'>&nbsp;
</span>#<span class=SpellE>pragma</span> <span class=GramE>warning(</span>disable:4512)</span></p>

<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'>&nbsp;</span><span
style='mso-spacerun:yes'>&nbsp;</span><span style='mso-spacerun:yes'>&nbsp;
</span>#<span class=SpellE>pragma</span> <span class=GramE>warning(</span>disable:4180)</span></p>

<p class=MsoNormal><span lang=EN-US><span
style='mso-spacerun:yes'>&nbsp;</span><span
style='mso-spacerun:yes'>&nbsp;</span><span style='mso-spacerun:yes'>&nbsp;
</span></span><span lang=EN-US style='font-family:"Arial Black"'>#include
&lt;boost/lambda/<span class=SpellE>lambda.hpp</span>&gt;<o:p></o:p></span></p>

<p class=MsoNormal><span lang=EN-US>#<span class=SpellE>pragma</span>
warning(pop)<span style='mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</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"'>恢复原来的警告级别</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
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"'>：“未使用的函数参数”</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。首先检查一下，确信你确实不需要使用该参数（例如：这可能是一个为了今后扩充而保留的占位符，或者是一个已标准化的标记（</span><span
lang=EN-US>signature</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>）的必需部分，对你的代码并没有用）。如果不需要，直接把该参数的名字在函数的参数列表中删除就行了：</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"'>在一个用户定义的</span><span
class=SpellE><span lang=EN-US>allocator</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"'>中，该</span><span class=SpellE><span
lang=EN-US>allocator</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"'>没有使用</span><span lang=EN-US>hint …<o:p></o:p></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"'>警告：“参数‘</span><span
class=SpellE><span lang=EN-US>localityHint</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"'>’未使用”</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span class=GramE><span lang=EN-US>pointer</span></span><span
lang=EN-US> allocate( <span class=SpellE>size_type</span> <span class=SpellE>numObjects</span>,
const void *<span class=SpellE>localityHint</span> = 0 ) {</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span><span class=GramE>return</span>
<span class=SpellE>static_cast</span>&lt;pointer&gt;( <span class=SpellE>mallocShared</span>(
<span class=SpellE>numObjects</span> * <span class=SpellE>sizeof</span>(T) ) );</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"'>新版本：消除了警告</span><span
lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span class=GramE><span lang=EN-US>pointer</span></span><span
lang=EN-US> allocate( <span class=SpellE>size_type</span> <span class=SpellE>numObjects</span>,
const void * /* <span class=SpellE>localityHint</span> */ = 0 ) {</span></p>

<p class=MsoNormal><span lang=EN-US><span style='mso-spacerun:yes'>&nbsp;
</span><span style='mso-spacerun:yes'>&nbsp;&nbsp;</span><span class=GramE>return</span>
<span class=SpellE>static_cast</span>&lt;pointer&gt;( <span class=SpellE>mallocShared</span>(
<span class=SpellE>numObjects</span> * <span class=SpellE>sizeof</span>(T) ));</span></p>

<p class=MsoNormal><span lang=EN-US>}</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"'>：“定义了变量却从未使用”</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。首先检查一下，确信你确实不需要引用该变量。（一个基于栈的</span><span lang=EN-US>RAII</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>对象经常会欺骗性地导致这个警告；参见第</span><span lang=EN-US>13</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>条）如果不需要，通常可以加一条对变量自身求值的表达式（该求值不会影响运行时的速度）：</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"'>警告：“定义了变量‘</span><span
lang=EN-US>lock</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"'>’却从未使用”</span><span lang=EN-US><o:p></o:p></span></i></p>

<p class=MsoNormal><span class=GramE><span lang=EN-US>void</span></span><span
lang=EN-US> Fun() {</span></p>

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

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

<p class=MsoNormal><span lang=EN-US><o:p>&nbsp;</o:p></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"'>新版本：可能消除了警告</span><span