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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="17.5.1.2.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="17.5.1.4.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="16.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="18.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="17.htm">17</a></span><span class="clause-title-previous"> Classes</span></span><span class="clause-depth"><a href="17.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="17.6.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="17.5.htm">17.5</a></span><span class="clause-title-previous"> Methods</span></span><span class="clause-depth"><a href="17.5.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="17.5.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="17.5.1.htm">17.5.1</a></span><span class="clause-title-previous"> Method parameters</span></span><span class="clause-depth"><a href="17.5.1.2.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="17.5.1.4.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">17.5.1.3</span><span class="clause-title"> Output parameters</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>A parameter declared with an out modifier is an output parameter.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>Similar to a reference parameter, an output parameter does not create a new storage location.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a>Instead, an output parameter represents the same storage location as the variable given as the argument in the method invocation.</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>When a formal parameter is an output parameter, the corresponding argument in a method invocation must consist of the keyword out followed by a <span class="non-terminal"><a href="12.4.htm#variable-reference">variable-reference</a></span> (<a href="12.3.3.htm">§12.3.3</a>) of the same type as the formal parameter.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>A variable need not be definitely assigned before it can be passed as an output parameter, but following an invocation where a variable was passed as an output parameter, the variable is considered definitely assigned.</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>Within a method, just like a local variable, an output parameter is initially considered unassigned and must be definitely assigned before its value is used.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>Every output parameter of a method must be definitely assigned before the method returns.</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>Output parameters are typically used in methods that produce multiple return values.</span> <span class="example">[Example: For example: <pre class="code-example">
using System;
class Test
{
static void SplitPath(string path, out string dir, out string name) {
int i = path.Length;
while (i > 0) {
char ch = path[i - 1];
if (ch == '\\' || ch == '/' || ch == ':') break;
i--;
}
dir = path.Substring(0, i);
name = path.Substring(i);
}
static void Main() {
string dir, name;
SplitPath("c:\\Windows\\System\\hello.txt", out dir, out name);
Console.WriteLine(dir);
Console.WriteLine(name);
}
}
</pre></span></span><span class="paragraph"><span class="example">The example produces the output: <pre class="code-example">
c:\Windows\System\
hello.txt
</pre></span></span><span class="paragraph"><span class="example">Note that the dir and name variables can be unassigned before they are passed to SplitPath, and that they are considered definitely assigned following the call. 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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