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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="14.5.10.3.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.5.12.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="13.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.htm">14</a></span><span class="clause-title-previous"> Expressions</span></span><span class="clause-depth"><a href="14.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.6.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.5.htm">14.5</a></span><span class="clause-title-previous"> Primary expressions</span></span><span class="clause-depth"><a href="14.5.10.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.5.12.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.5.11</span><span class="clause-title"> The typeof operator</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 typeof operator is used to obtain the System.Type object for a type.</span> <span class="grammar-production"><span class="name"><a name="typeof-expression"></a>typeof-expression</span> : <span class="rhs"><span class="keyword">typeof</span> <span class="terminal">(</span> <span class="non-terminal"><a href="11.htm#type">type</a></span> <span class="terminal">)</span> </span><span class="rhs"><span class="keyword">typeof</span> <span class="terminal">(</span> <span class="keyword">void</span> <span class="terminal">)</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 first form of <span class="non-terminal"><a href="14.5.11.htm#typeof-expression">typeof-expression</a></span> consists of a typeof keyword followed by a parenthesized type.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>The result of an expression of this form is the System.Type object for the indicated type.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>There is only one System.Type object for any given type.</span> <span class="note">[Note: This means that for type T, typeof(T) == typeof(T) is always true. end note]</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>The second form of <span class="non-terminal"><a href="14.5.11.htm#typeof-expression">typeof-expression</a></span> consists of a typeof keyword followed by a parenthesized <span class="keyword">void</span> keyword.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>The result of an expression of this form is the System.Type object that represents the absence of a type.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P3S3"></a>The type object returned by typeof(<span class="keyword">void</span>) is distinct from the type object returned for any type.</span> </span><span class="paragraph"><span class="note">[Note: This special type object is useful in class libraries that allow reflection onto methods in the language, where those methods wish to have a way to represent the return type of any method, including <span class="keyword">void</span> methods, with an instance of System.Type. end note]</span> </span><span class="paragraph"><span class="example">[Example: The example <pre class="code-example">
using System;
class Test
{
static void Main() {
Type[] t = {
typeof(int),
typeof(System.Int32),
typeof(string),
typeof(double[]),
typeof(void) };
for (int i = 0; i < t.Length; i++) {
Console.WriteLine(t[i].FullName);
}
}
}
</pre>produces the following output: <pre class="code-example">
System.Int32
System.Int32
System.String
System.Double[]
System.Void
</pre></span></span><span class="paragraph"><span class="example">Note that <span class="keyword">int</span> and System.Int32 are the same type. 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
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