📄 item_024.htm
字号:
<html xmlns:v="urn:schemas-microsoft-com:vml"
xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:w="urn:schemas-microsoft-com:office:word"
xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=gb2312">
<meta name=ProgId content=Word.Document>
<meta name=Generator content="Microsoft Word 11">
<meta name=Originator content="Microsoft Word 11">
<link rel=File-List href="filelist-24.xml.css" tppabs="http://www.gesoftfactory.com/developer/cppcodingstandards/Item_024_files/filelist.xml">
<title>24</title>
<!--[if gte mso 9]><xml>
<o:DocumentProperties>
<o:Author>SGuy</o:Author>
<o:LastAuthor>Dove</o:LastAuthor>
<o:Revision>2</o:Revision>
<o:TotalTime>5</o:TotalTime>
<o:Created>2005-08-07T04:18:00Z</o:Created>
<o:LastSaved>2005-08-07T04:18:00Z</o:LastSaved>
<o:Pages>1</o:Pages>
<o:Words>105</o:Words>
<o:Characters>603</o:Characters>
<o:Lines>5</o:Lines>
<o:Paragraphs>1</o:Paragraphs>
<o:CharactersWithSpaces>707</o:CharactersWithSpaces>
<o:Version>11.5606</o:Version>
</o:DocumentProperties>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:WordDocument>
<w:SpellingState>Clean</w:SpellingState>
<w:GrammarState>Clean</w:GrammarState>
<w:PunctuationKerning/>
<w:DrawingGridVerticalSpacing>7.8 pt</w:DrawingGridVerticalSpacing>
<w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery>
<w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:Compatibility>
<w:SpaceForUL/>
<w:BalanceSingleByteDoubleByteWidth/>
<w:DoNotLeaveBackslashAlone/>
<w:ULTrailSpace/>
<w:DoNotExpandShiftReturn/>
<w:AdjustLineHeightInTable/>
<w:BreakWrappedTables/>
<w:SnapToGridInCell/>
<w:WrapTextWithPunct/>
<w:UseAsianBreakRules/>
<w:DontGrowAutofit/>
<w:UseFELayout/>
</w:Compatibility>
<w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel>
</w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" LatentStyleCount="156">
</w:LatentStyles>
</xml><![endif]-->
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;
mso-font-charset:2;
mso-generic-font-family:auto;
mso-font-pitch:variable;
mso-font-signature:0 268435456 0 0 -2147483648 0;}
@font-face
{font-family:宋体;
panose-1:2 1 6 0 3 1 1 1 1 1;
mso-font-alt:SimSun;
mso-font-charset:134;
mso-generic-font-family:auto;
mso-font-pitch:variable;
mso-font-signature:3 135135232 16 0 262145 0;}
@font-face
{font-family:"\@宋体";
panose-1:2 1 6 0 3 1 1 1 1 1;
mso-font-charset:134;
mso-generic-font-family:auto;
mso-font-pitch:variable;
mso-font-signature:3 135135232 16 0 262145 0;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{mso-style-parent:"";
margin:0cm;
margin-bottom:.0001pt;
mso-pagination:widow-orphan;
font-size:12.0pt;
font-family:"Times New Roman";
mso-fareast-font-family:宋体;}
h3
{mso-style-next:Normal;
margin-top:12.0pt;
margin-right:0cm;
margin-bottom:3.0pt;
margin-left:0cm;
mso-pagination:widow-orphan;
page-break-after:avoid;
mso-outline-level:3;
font-size:13.0pt;
font-family:Arial;}
span.SpellE
{mso-style-name:"";
mso-spl-e:yes;}
span.GramE
{mso-style-name:"";
mso-gram-e:yes;}
/* Page Definitions */
@page
{mso-page-border-surround-header:no;
mso-page-border-surround-footer:no;}
@page Section1
{size:595.3pt 841.9pt;
margin:72.0pt 90.0pt 72.0pt 90.0pt;
mso-header-margin:42.55pt;
mso-footer-margin:49.6pt;
mso-paper-source:0;
layout-grid:15.6pt;}
div.Section1
{page:Section1;}
/* List Definitions */
@list l0
{mso-list-id:16204290;
mso-list-type:hybrid;
mso-list-template-ids:-323730282 67698689 67698691 67698693 67698689 67698691 67698693 67698689 67698691 67698693;}
@list l0:level1
{mso-level-number-format:bullet;
mso-level-text:\F0B7;
mso-level-tab-stop:36.0pt;
mso-level-number-position:left;
text-indent:-18.0pt;
font-family:Symbol;}
@list l1
{mso-list-id:1462336193;
mso-list-type:hybrid;
mso-list-template-ids:-62620550 67698689 67698691 67698693 67698689 67698691 67698693 67698689 67698691 67698693;}
@list l1:level1
{mso-level-number-format:bullet;
mso-level-text:\F0B7;
mso-level-tab-stop:36.0pt;
mso-level-number-position:left;
text-indent:-18.0pt;
font-family:Symbol;}
ol
{margin-bottom:0cm;}
ul
{margin-bottom:0cm;}
-->
</style>
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-parent:"";
mso-padding-alt:0cm 5.4pt 0cm 5.4pt;
mso-para-margin:0cm;
mso-para-margin-bottom:.0001pt;
mso-pagination:widow-orphan;
font-size:10.0pt;
font-family:"Times New Roman";
mso-ansi-language:#0400;
mso-fareast-language:#0400;
mso-bidi-language:#0400;}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="2050"/>
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1"/>
</o:shapelayout></xml><![endif]-->
</head>
<body lang=ZH-CN style='tab-interval:21.0pt;text-justify-trim:punctuation'>
<div class=Section1 style='layout-grid:15.6pt'>
<h3><span lang=EN-US>24</span><span style='font-family:宋体;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial'>．始终用内部</span><span lang=EN-US>#include</span><span
style='font-family:宋体;mso-ascii-font-family:Arial;mso-hansi-font-family:Arial'>防护哨。绝对不要用外部</span><span
lang=EN-US>#include</span><span style='font-family:宋体;mso-ascii-font-family:
Arial;mso-hansi-font-family:Arial'>防护哨。</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"'>戴上头（文件）盔：对所有的头文件，用内部</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"'>防护哨和唯一的名字来防止无意中的多重多含。</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 style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>每个头文件应该用内部</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"'>防护哨，以避免万一头文件被包含了多次而导致的多重定义。例如，一个名为</span><span class=SpellE><span
lang=EN-US>foo.h</span></span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的头文件应该遵循以下一般形式：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>#<span class=SpellE>ifndef</span>
FOO_H_INCLUDED_</span></p>
<p class=MsoNormal><span lang=EN-US>#define FOO_H_INCLUDED_</span></p>
<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>//
... contents of the <span class=GramE>file ...</span><o:p></o:p></span></i></p>
<p class=MsoNormal><span lang=EN-US>#<span class=SpellE>endif</span></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"'>在定义包含防护哨的时候，请注意以下规则：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l0 level1 lfo1;tab-stops:list 36.0pt'><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"'>使用唯一的防护哨名</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>：确保该名字至少在应用程序中是唯一的。在前面我们使用了一个很流行的约定。防护哨名可以包含应用程序的名字，有些工具生成的防护哨名包含了随机数。</span></li>
</ul>
<p class=MsoNormal style='margin-left:18.0pt'><span lang=EN-US><o:p> </o:p></span></p>
<ul style='margin-top:0cm' type=disc>
<li class=MsoNormal style='mso-list:l1 level1 lfo2;tab-stops:list 36.0pt'><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"'>别耍小聪明</span></i><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>：不要在被防护的部分之外放任何代码或注释，坚持使用前面给出的标准形式。如今的编译器能够检测包含防护哨，但它们的智能度可能是有限的并希望防护哨代码只出现在头文件的开始和结尾处。</span></li>
</ul>
<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"'>避免使用一些老书中提倡而现在已经过时了的外部包含防护哨：</span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal style='tab-stops:198.0pt'><span lang=EN-US>#<span
class=SpellE>ifdef</span> FOO_H_INCLUDED_<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"'>不建议</span></p>
<p class=MsoNormal><span lang=EN-US>#include “<span class=SpellE>foo.h</span>”</span></p>
<p class=MsoNormal><span lang=EN-US>#define FOO_H_INCLUDED_</span></p>
<p class=MsoNormal><span lang=EN-US>#<span class=SpellE>endif</span></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"'>外部包含防护哨很乏味，在如今的编译器看来已经过时，另外，这种方法非常脆弱，因为调用者和头文件必须就防护哨名达成一致，而这导致了紧耦合。</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"'>例外</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"'>在极少的情况下，可能有意将某个头文件包含多次。</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"'>参考资料</span><span lang=EN-US><o:p></o:p></span></b></p>
<p class=MsoNormal><i style='mso-bidi-font-style:normal'><span lang=EN-US>[C++03</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>§2.1] · [Stroustrup00] §9.3.3</span></i></p>
</div>
</body>
</html>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -