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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="15.9.5.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="15.11.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="15.9.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.11.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">15.10</span><span class="clause-title"> The try 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 try statement provides a mechanism for catching exceptions that occur during execution of a block.</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>Furthermore, the try statement provides the ability to specify a block of code that is always executed when control leaves the try statement.</span> <span class="grammar-production"><span class="name"><a name="try-statement"></a>try-statement</span> : <span class="rhs"><span class="keyword">try</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> <span class="non-terminal"><a href="15.10.htm#catch-clauses">catch-clauses</a></span> </span><span class="rhs"><span class="keyword">try</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> <span class="non-terminal"><a href="15.10.htm#finally-clause">finally-clause</a></span> </span><span class="rhs"><span class="keyword">try</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> <span class="non-terminal"><a href="15.10.htm#catch-clauses">catch-clauses</a></span> <span class="non-terminal"><a href="15.10.htm#finally-clause">finally-clause</a></span> </span></span><span class="grammar-production"><span class="name"><a name="catch-clauses"></a>catch-clauses</span> : <span class="rhs"><span class="non-terminal"><a href="15.10.htm#specific-catch-clauses">specific-catch-clauses</a></span> <span class="non-terminal"><a href="15.10.htm#general-catch-clause">general-catch-clause</a></span><sub>opt</sub> </span><span class="rhs"><span class="non-terminal"><a href="15.10.htm#specific-catch-clauses">specific-catch-clauses</a></span><sub>opt</sub> <span class="non-terminal"><a href="15.10.htm#general-catch-clause">general-catch-clause</a></span> </span></span><span class="grammar-production"><span class="name"><a name="specific-catch-clauses"></a>specific-catch-clauses</span> : <span class="rhs"><span class="non-terminal"><a href="15.10.htm#specific-catch-clause">specific-catch-clause</a></span> </span><span class="rhs"><span class="non-terminal"><a href="15.10.htm#specific-catch-clauses">specific-catch-clauses</a></span> <span class="non-terminal"><a href="15.10.htm#specific-catch-clause">specific-catch-clause</a></span> </span></span><span class="grammar-production"><span class="name"><a name="specific-catch-clause"></a>specific-catch-clause</span> : <span class="rhs"><span class="keyword">catch</span> <span class="terminal">(</span> <span class="non-terminal"><a href="11.2.htm#class-type">class-type</a></span> <span class="non-terminal"><a href="9.4.2.htm#identifier">identifier</a></span><sub>opt</sub> <span class="terminal">)</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> </span></span><span class="grammar-production"><span class="name"><a name="general-catch-clause"></a>general-catch-clause</span> : <span class="rhs"><span class="keyword">catch</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> </span></span><span class="grammar-production"><span class="name"><a name="finally-clause"></a>finally-clause</span> : <span class="rhs"><span class="keyword">finally</span> <span class="non-terminal"><a href="15.2.htm#block">block</a></span> </span></span></span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>There are three possible forms of try statements: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a> A try block followed by one or more catch blocks.</span> </li><li><span class="sentence"><span class="sentence-number">3</span> <a name="P3S3"></a> A try block followed by a finally block.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P3S4"></a> A try block followed by one or more catch blocks followed by a finally block.</span> </li></ul></span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>When a catch clause specifies a <span class="non-terminal"><a href="11.2.htm#class-type">class-type</a></span>, the type must be System.Exception or a type that derives from System.Exception.</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 a catch clause specifies both a <span class="non-terminal"><a href="11.2.htm#class-type">class-type</a></span> and an identifier, an exception variable of the given name and type is declared.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>The exception variable corresponds to a local variable with a scope that extends over the catch block.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>During execution of the catch block, the exception variable represents the exception currently being handled.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a>For purposes of definite assignment checking, the exception variable is considered definitely assigned in its entire scope.</span> </span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>Unless a catch clause includes an exception variable name, it is impossible to access the exception object in the catch block.</span> </span><span class="locator">
Paragraph 7</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P7S1"></a>A catch clause that specifies neither an exception type nor an exception variable name is called a general catch clause.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P7S2"></a>A try statement can only have one general catch clause, and if one is present it must be the last catch clause.</span> </span><span class="paragraph"><span class="note">[Note: Some environments, especially those supporting multiple languages, may support exceptions that are not representable as an object derived from System.Exception, although such an exception could never be generated by C# code. In such an environment, a general catch clause might be used to catch such an exception. Thus, a general catch clause is semantically different from one that specifies the type System.Exception, in that the former may also catch exceptions from other languages. end note]</span> </span><span class="locator">
Paragraph 8</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P8S1"></a>In order to locate a handler for an exception, catch clauses are examined in lexical order.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P8S2"></a>A compile-time error occurs if a catch clause specifies a type that is the same as, or is derived from, a type that was specified in an earlier catch clause for the same try.</span> <span class="note">[Note: Without this restriction, it would be possible to write unreachable catch clauses. end note]</span> </span><span class="locator">
Paragraph 9</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P9S1"></a>Within a catch block, a throw statement (<a href="15.9.5.htm">§15.9.5</a>) with no expression can be used to re-throw the exception that was caught by the catch block.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P9S2"></a>Assignments to an exception variable do not alter the exception that is re-thrown.</span> </span><span class="paragraph"><span class="example">[Example: In the example <pre class="code-example">
using System;
class Test
{
static void F() {
try {
G();
}
catch (Exception e) {
Console.WriteLine("Exception in F: " + e.Message);
e = new Exception("F");
throw; // re-throw
}
}
static void G() {
throw new Exception("G");
}
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