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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="12.1.6.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="12.2.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="11.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="13.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="12.htm">12</a></span><span class="clause-title-previous"> Variables</span></span><span class="clause-depth"><a href="12.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="12.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="12.1.htm">12.1</a></span><span class="clause-title-previous"> Variable categories</span></span><span class="clause-depth"><a href="12.1.6.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="12.1.7.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">12.1.7</span><span class="clause-title"> Local variables</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 local variable is declared by a <span class="non-terminal"><a href="15.5.1.htm#local-variable-declaration">local-variable-declaration</a></span>, which may occur in a block, a <span class="non-terminal"><a href="15.8.3.htm#for-statement">for-statement</a></span>, a <span class="non-terminal"><a href="15.7.2.htm#switch-statement">switch-statement</a></span>, or a <span class="non-terminal"><a href="15.13.htm#using-statement">using-statement</a></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 lifetime of a local variable is the portion of program execution during which storage is guaranteed to be reserved for it.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>This lifetime extends from entry into the block, <span class="non-terminal"><a href="15.8.3.htm#for-statement">for-statement</a></span>, <span class="non-terminal"><a href="15.7.2.htm#switch-statement">switch-statement</a></span>, or <span class="non-terminal"><a href="15.13.htm#using-statement">using-statement</a></span> with which it is associated, until execution of that block, <span class="non-terminal"><a href="15.8.3.htm#for-statement">for-statement</a></span>, <span class="non-terminal"><a href="15.7.2.htm#switch-statement">switch-statement</a></span>, or <span class="non-terminal"><a href="15.13.htm#using-statement">using-statement</a></span> ends in any way.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>(Entering an enclosed block or calling a method suspends, but does not end, execution of the current block, <span class="non-terminal"><a href="15.8.3.htm#for-statement">for-statement</a></span>, <span class="non-terminal"><a href="15.7.2.htm#switch-statement">switch-statement</a></span>, or <span class="non-terminal"><a href="15.13.htm#using-statement">using-statement</a></span>.)</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a>If the parent block, <span class="non-terminal"><a href="15.8.3.htm#for-statement">for-statement</a></span>, <span class="non-terminal"><a href="15.7.2.htm#switch-statement">switch-statement</a></span>, or <span class="non-terminal"><a href="15.13.htm#using-statement">using-statement</a></span> is entered recursively, a new instance of the local variable is created each time, and its <span class="non-terminal"><a href="15.5.1.htm#local-variable-initializer">local-variable-initializer</a></span>, if any, is evaluated each time.</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>A local variable is not automatically initialized and thus has no default value.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>For the purpose of definite assignment checking, a local variable is considered initially unassigned.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P3S3"></a>A <span class="non-terminal"><a href="15.5.1.htm#local-variable-declaration">local-variable-declaration</a></span> may include a <span class="non-terminal"><a href="15.5.1.htm#local-variable-initializer">local-variable-initializer</a></span>, in which case the variable is considered definitely assigned in its entire scope, except within the expression provided in the <span class="non-terminal"><a href="15.5.1.htm#local-variable-initializer">local-variable-initializer</a></span>.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>Within the scope of a local variable, it is a compile-time error to refer to that local variable in a textual position that precedes its <span class="non-terminal"><a href="15.5.1.htm#local-variable-declarator">local-variable-declarator</a></span>.</span> </span><span class="paragraph"><span class="note">[Note: The actual lifetime of a local variable is implementation-dependent. For example, a compiler might statically determine that a local variable in a block is only used for a small portion of that block. Using this analysis, the compiler could generate code that results in the variable's storage having a shorter lifetime than its containing block. </span></span><span class="paragraph"><span class="note">The storage referred to by a local reference variable is reclaimed independently of the lifetime of that local reference variable (<a href="10.9.htm">§10.9</a>). end note]</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 local variable is also declared by a <span class="non-terminal"><a href="15.8.4.htm#foreach-statement">foreach-statement</a></span> and by a <span class="non-terminal"><a href="15.10.htm#specific-catch-clause">specific-catch-clause</a></span> for a <span class="non-terminal"><a href="15.10.htm#try-statement">try-statement</a></span>.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>For a <span class="non-terminal"><a href="15.8.4.htm#foreach-statement">foreach-statement</a></span>, the local variable is an iteration variable (<a href="15.8.4.htm">§15.8.4</a>).</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>For a <span class="non-terminal"><a href="15.10.htm#specific-catch-clause">specific-catch-clause</a></span>, the local variable is an exception variable (<a href="15.10.htm">§15.10</a>).</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a>A local variable declared by a <span class="non-terminal"><a href="15.8.4.htm#foreach-statement">foreach-statement</a></span> or <span class="non-terminal"><a href="15.10.htm#specific-catch-clause">specific-catch-clause</a></span> is considered definitely assigned in its entire scope.</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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