📄 9.5.3.htm

📁 This ECMA Standard specifies the form and establishes the interpretation of programs written in the
💻 HTM
字号:
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Hyperlinked ECMA C# Language Specification</title><meta name="author" content="Jon Jagger" /><link rel="stylesheet" href="ecma334.css"></link></head><body><div align="right"><em><a href="http://www.jaggersoft.com">Jon Jagger</a></em></div><div align="right"><a href="mailto:jon@jaggersoft.com">jon@jaggersoft.com</a></div><form method="get" action="http://search.atomz.com/search/"><input size="30" name="sp-q"></input><input type="submit" value="Search C# Spec"></input><input type="hidden" name="sp-a" value="sp10024177"></input><input type="hidden" name="sp-f" value="ISO-8859-1"></input></form><a href="toc.htm">Table of Contents</a> <a href="1.htm">1</a> <a href="2.htm">2</a> <a href="3.htm">3</a> <a href="4.htm">4</a> <a href="5.htm">5</a> <a href="6.htm">6</a> <a href="7.htm">7</a> <a href="8.htm">8</a> <a href="9.htm">9</a> <a href="10.htm">10</a> <a href="11.htm">11</a> <a href="12.htm">12</a> <a href="13.htm">13</a> <a href="14.htm">14</a> <a href="15.htm">15</a> <a href="16.htm">16</a> <a href="17.htm">17</a> <a href="18.htm">18</a> <a href="19.htm">19</a> <a href="20.htm">20</a> <a href="21.htm">21</a> <a href="22.htm">22</a> <a href="23.htm">23</a> <a href="24.htm">24</a> <a href="25.htm">25</a> <a href="notes.htm">Notes</a> <a href="HyperlinkedCSharpECMA.zip">Download</a><span class="ruler"></span><span class="heading">ECMA-334 C# Language Specification</span><span class="navigate"><a href="9.5.2.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="9.5.4.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="8.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="10.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="9.htm">9</a></span><span class="clause-title-previous"> Lexical structure</span></span><span class="clause-depth"><a href="9.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="9.5.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="9.5.htm">9.5</a></span><span class="clause-title-previous"> Pre-processing directives</span></span><span class="clause-depth"><a href="9.5.2.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="9.5.4.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">9.5.3</span><span class="clause-title"> Declaration directives</span></span><span class="locator">
     Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>The declaration directives are used to define or undefine conditional compilation symbols.</span> <span class="grammar-production"><span class="name"><a name="pp-declaration"></a>pp-declaration</span> :: <span class="rhs"><span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span><sub>opt</sub> <span class="terminal">#</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span><sub>opt</sub> <span class="terminal">define</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span> <span class="non-terminal"><a href="9.5.1.htm#conditional-symbol">conditional-symbol</a></span> <span class="non-terminal"><a href="9.5.3.htm#pp-new-line">pp-new-line</a></span> </span><span class="rhs"><span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span><sub>opt</sub> <span class="terminal">#</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span><sub>opt</sub> <span class="terminal">undef</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span> <span class="non-terminal"><a href="9.5.1.htm#conditional-symbol">conditional-symbol</a></span> <span class="non-terminal"><a href="9.5.3.htm#pp-new-line">pp-new-line</a></span> </span></span><span class="grammar-production"><span class="name"><a name="pp-new-line"></a>pp-new-line</span> :: <span class="rhs"><span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span><sub>opt</sub> <span class="non-terminal"><a href="9.3.2.htm#single-line-comment">single-line-comment</a></span><sub>opt</sub> <span class="non-terminal"><a href="9.3.1.htm#new-line">new-line</a></span> </span></span></span><span class="locator">
     Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>The processing of a <span class="symbol">#define</span> directive causes the given conditional compilation symbol to become defined, starting with the source line that follows the directive.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>Likewise, the processing of an <span class="symbol">#undef</span> directive causes the given conditional compilation symbol to become undefined, starting with the source line that follows the directive.</span> </span><span class="locator">
     Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>Any <span class="symbol">#define</span> and <span class="symbol">#undef</span> directives in a source file must occur before the first token (<a href="9.4.htm">&#167;9.4</a>) in the source file; otherwise a compile-time error occurs.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>In intuitive terms, <span class="symbol">#define</span> and <span class="symbol">#undef</span> directives must precede any "real code" in the source file.</span> </span><span class="paragraph"><span class="example">[Example: The example: <pre class="code-example">
#define Enterprise  
#if Professional || Enterprise  
#define Advanced  
#endif  
namespace Megacorp.Data  
{  
   #if Advanced  
   class PivotTable {...}  
   #endif  
}  
</pre>is valid because the <span class="symbol">#define</span> directives precede the first token (the namespace keyword) in the source file. end example]</span> </span><span class="paragraph"><span class="example">[Example: The following example results in a compile-time error because a <span class="symbol">#define</span> follows real code: <pre class="code-example">
#define A  
namespace N  
{  
   #define B  
   #if B  
   class Class1 {}  
   #endif  
}  
</pre>end example]</span> </span><span class="locator">
     Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>A <span class="symbol">#define</span> may define a conditional compilation symbol that is already defined, without there being any intervening <span class="symbol">#undef</span> for that symbol.</span> <span class="example">[Example: The example below defines a conditional compilation symbol A and then defines it again. <pre class="code-example">
#define A  
#define A  
</pre></span></span><span class="paragraph"><span class="example">For compilers that allow conditional compilation symbols to be defined as compilation options, an alternative way for such redefinition to occur is to define the symbol as a compiler option as well as in the source. end example]</span> </span><span class="locator">
     Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>A <span class="symbol">#undef</span> may "undefine" a conditional compilation symbol that is not defined.</span> <span class="example">[Example: The example below defines a conditional compilation symbol A and then undefines it twice; although the second <span class="symbol">#undef</span> has no effect, it is still valid. <pre class="code-example">
#define A  
#undef A  
#undef A  
</pre>end example]</span> </span><span class="ruler"></span><table><tr><td><table align="left" bgcolor="navy"><tr bgcolor="navy"><td><font face="Arial,sans-serif" size="6" color="yellow"><strong>{ JSL }</strong></font></td></tr></table></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Jagger Software Ltd</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Company # 4070126</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>VAT # 762 5213 42</strong></font></td></tr></table><img src="valid-html401.png" align="left" height="31" width="88" alt="Valid HTML 4.01" /><img src="vcss.gif" align="left" height="31" width="88" alt="Valid CSS" /></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 + -