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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="15.9.4.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="15.10.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="14.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="16.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="15.htm">15</a></span><span class="clause-title-previous"> Statements</span></span><span class="clause-depth"><a href="15.8.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.10.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="15.9.htm">15.9</a></span><span class="clause-title-previous"> Jump statements</span></span><span class="clause-depth"><a href="15.9.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.9.5.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">15.9.5</span><span class="clause-title"> The throw statement</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 throw statement throws an exception.</span> <span class="grammar-production"><span class="name"><a name="throw-statement"></a>throw-statement</span> : <span class="rhs"><span class="keyword">throw</span> <span class="non-terminal"><a href="14.14.htm#expression">expression</a></span><sub>opt</sub> <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>A throw statement with an expression throws the value produced by evaluating the expression.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>The expression must denote a value of the class type System.Exception or of a class type that derives from System.Exception.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>If evaluation of the expression produces null, a System.NullReferenceException is thrown instead.</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 throw statement with no expression can be used only in a catch block, in which case, that statement re-throws the exception that is currently being handled by that catch block.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>Because a throw statement unconditionally transfers control elsewhere, the end point of a throw statement is never reachable.</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>When an exception is thrown, control is transferred to the first catch clause in an enclosing try statement that can handle the exception.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>The process that takes place from the point of the exception being thrown to the point of transferring control to a suitable exception handler is known as exception propagation.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>Propagation of an exception consists of repeatedly evaluating the following steps until a catch clause that matches the exception is found.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a>In this description, the throw point is initially the location at which the exception is thrown.</span> <ul><li><span class="sentence"><span class="sentence-number">5</span> <a name="P5S5"></a> In the current function member, each try statement that encloses the throw point is examined.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P5S6"></a>For each statement S, starting with the innermost try statement and ending with the outermost try statement, the following steps are evaluated: </span></li><ul><li><span class="sentence"><span class="sentence-number">7</span> <a name="P5S7"></a> If the try block of S encloses the throw point and if S has one or more catch clauses, the catch clauses are examined in order of appearance to locate a suitable handler for the exception.</span> <span class="sentence"><span class="sentence-number">8</span> <a name="P5S8"></a>The first catch clause that specifies the exception type or a base type of the exception type is considered a match.</span> <span class="sentence"><span class="sentence-number">9</span> <a name="P5S9"></a>A general catch (<a href="15.10.htm">§15.10</a>) clause is considered a match for any exception type.</span> <span class="sentence"><span class="sentence-number">10</span> <a name="P5S10"></a>If a matching catch clause is located, the exception propagation is completed by transferring control to the block of that catch clause.</span> </li><li><span class="sentence"><span class="sentence-number">11</span> <a name="P5S11"></a> Otherwise, if the try block or a catch block of S encloses the throw point and if S has a finally block, control is transferred to the finally block.</span> <span class="sentence"><span class="sentence-number">12</span> <a name="P5S12"></a>If the finally block throws another exception, processing of the current exception is terminated.</span> <span class="sentence"><span class="sentence-number">13</span> <a name="P5S13"></a>Otherwise, when control reaches the end point of the finally block, processing of the current exception is continued.</span> </li></ul><li><span class="sentence"><span class="sentence-number">14</span> <a name="P5S14"></a> If an exception handler was not located in the current function member invocation, the function member invocation is terminated.</span> <span class="sentence"><span class="sentence-number">15</span> <a name="P5S15"></a>The steps above are then repeated for the caller of the function member with a throw point corresponding to the statement from which the function member was invoked.</span> </li><li><span class="sentence"><span class="sentence-number">16</span> <a name="P5S16"></a> If the exception processing terminates all function member invocations in the current thread, indicating that the thread has no handler for the exception, then the thread is itself terminated.</span> <span class="sentence"><span class="sentence-number">17</span> <a name="P5S17"></a>The impact of such termination is implementation-defined.</span> </li></ul></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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