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<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="9.5.3.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="9.5.5.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="9.5.3.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="9.5.5.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">9.5.4</span><span class="clause-title"> Conditional compilation 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 conditional compilation directives are used to conditionally include or exclude portions of a source file.</span> <span class="grammar-production"><span class="name"><a name="pp-conditional"></a>pp-conditional</span> :: <span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#pp-if-section">pp-if-section</a></span> <span class="non-terminal"><a href="9.5.4.htm#pp-elif-sections">pp-elif-sections</a></span><sub>opt</sub> <span class="non-terminal"><a href="9.5.4.htm#pp-else-section">pp-else-section</a></span><sub>opt</sub> <span class="non-terminal"><a href="9.5.4.htm#pp-endif">pp-endif</a></span> </span></span><span class="grammar-production"><span class="name"><a name="pp-if-section"></a>pp-if-section</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">if</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span> <span class="non-terminal"><a href="9.5.2.htm#pp-expression">pp-expression</a></span> <span class="non-terminal"><a href="9.5.3.htm#pp-new-line">pp-new-line</a></span> <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span><sub>opt</sub> </span></span><span class="grammar-production"><span class="name"><a name="pp-elif-sections"></a>pp-elif-sections</span> :: <span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#pp-elif-section">pp-elif-section</a></span> </span><span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#pp-elif-sections">pp-elif-sections</a></span> <span class="non-terminal"><a href="9.5.4.htm#pp-elif-section">pp-elif-section</a></span> </span></span><span class="grammar-production"><span class="name"><a name="pp-elif-section"></a>pp-elif-section</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">elif</span> <span class="non-terminal"><a href="9.3.3.htm#whitespace">whitespace</a></span> <span class="non-terminal"><a href="9.5.2.htm#pp-expression">pp-expression</a></span> <span class="non-terminal"><a href="9.5.3.htm#pp-new-line">pp-new-line</a></span> <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span><sub>opt</sub> </span></span><span class="grammar-production"><span class="name"><a name="pp-else-section"></a>pp-else-section</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">else</span> <span class="non-terminal"><a href="9.5.3.htm#pp-new-line">pp-new-line</a></span> <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span><sub>opt</sub> </span></span><span class="grammar-production"><span class="name"><a name="pp-endif"></a>pp-endif</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">endif</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="conditional-section"></a>conditional-section</span> :: <span class="rhs"><span class="non-terminal"><a href="9.3.htm#input-section">input-section</a></span> </span><span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#skipped-section">skipped-section</a></span> </span></span><span class="grammar-production"><span class="name"><a name="skipped-section"></a>skipped-section</span> :: <span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#skipped-section-part">skipped-section-part</a></span> </span><span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#skipped-section">skipped-section</a></span> <span class="non-terminal"><a href="9.5.4.htm#skipped-section-part">skipped-section-part</a></span> </span></span><span class="grammar-production"><span class="name"><a name="skipped-section-part"></a>skipped-section-part</span> :: <span class="rhs"><span class="non-terminal"><a href="9.5.4.htm#skipped-characters">skipped-characters</a></span><sub>opt</sub> <span class="non-terminal"><a href="9.3.1.htm#new-line">new-line</a></span> </span><span class="rhs"><span class="non-terminal"><a href="9.5.htm#pp-directive">pp-directive</a></span> </span></span><span class="grammar-production"><span class="name"><a name="skipped-characters"></a>skipped-characters</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="9.5.4.htm#not-number-sign">not-number-sign</a></span> <span class="non-terminal"><a href="9.3.2.htm#input-characters">input-characters</a></span><sub>opt</sub> </span></span><span class="grammar-production"><span class="name"><a name="not-number-sign"></a>not-number-sign</span> :: <span class="rhs">Any <span class="non-terminal"><a href="9.3.2.htm#input-character">input-character</a></span> except # </span></span></span><span class="paragraph"><span class="note">[Note: As indicated by the syntax, conditional compilation directives must be written as sets consisting of, in order, an <span class="symbol">#if</span> directive, zero or more <span class="symbol">#elif</span> directives, zero or one <span class="symbol">#else</span> directive, and an <span class="symbol">#endif</span> directive. Between the directives are conditional sections of source code. Each section is controlled by the immediately preceding directive. A conditional section may itself contain nested conditional compilation directives provided these directives form complete sets. end note]</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>A <span class="non-terminal"><a href="9.5.4.htm#pp-conditional">pp-conditional</a></span> selects at most one of the contained <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span>s for normal lexical processing: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a> The <span class="non-terminal"><a href="9.5.2.htm#pp-expression">pp-expression</a></span>s of the <span class="symbol">#if</span> and <span class="symbol">#elif</span> directives are evaluated in order until one yields true.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>If an expression yields true, the <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span> of the corresponding directive is selected.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a> If all <span class="non-terminal"><a href="9.5.2.htm#pp-expression">pp-expression</a></span>s yield false, and if an <span class="symbol">#else</span> directive is present, the <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span> of the <span class="symbol">#else</span> directive is selected.</span> </li><li><span class="sentence"><span class="sentence-number">5</span> <a name="P2S5"></a> Otherwise, no <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span> is selected.</span> </li></ul></span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>The selected <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span>, if any, is processed as a normal input-section: the source code contained in the section must adhere to the lexical grammar; tokens are generated from the source code in the section; and pre-processing directives in the section have the prescribed effects.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>The remaining <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span>s, if any, are processed as skipped-sections: except for pre-processing directives, the source code in the section need not adhere to the lexical grammar; no tokens are generated from the source code in the section; and pre-processing directives in the section must be lexically correct but are not otherwise processed.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>Within a <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span> that is being processed as a <span class="non-terminal"><a href="9.5.4.htm#skipped-section">skipped-section</a></span>, any nested <span class="non-terminal"><a href="9.5.4.htm#conditional-section">conditional-section</a></span>s (contained in nested <span class="symbol">#if</span>...<span class="symbol">#endif</span> and <span class="symbol">#region</span>...<span class="symbol">#endregion</span> constructs) are also processed as <span class="non-terminal"><a href="9.5.4.htm#skipped-section">skipped-section</a></span>s.</span> </span><span class="paragraph"><span class="example">[Example: The following example illustrates how conditional compilation directives can nest: <pre class="code-example">
#define Debug // Debugging on
#undef Trace // Tracing off
class PurchaseTransaction
{
void Commit() {
#if Debug
CheckConsistency();
#if Trace
WriteToLog(this.ToString());
#endif
#endif
CommitHelper();
}
}
</pre></span></span><span class="paragraph"><span class="example">Except for pre-processing directives, skipped source code is not subject to lexical analysis. For example, the following is valid despite the unterminated comment in the <span class="symbol">#else</span> section: <pre class="code-example">
#define Debug // Debugging on
class PurchaseTransaction
{
void Commit() {
#if Debug
CheckConsistency();
#else
/* Do something else
#endif
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