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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="14.11.2.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.13.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="14.11.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.13.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.12</span><span class="clause-title"> Conditional 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 ?: operator is called the conditional operator.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>It is at times also called the ternary operator.</span> <span class="grammar-production"><span class="name"><a name="conditional-expression"></a>conditional-expression</span> : <span class="rhs"><span class="non-terminal"><a href="14.11.htm#conditional-or-expression">conditional-or-expression</a></span> </span><span class="rhs"><span class="non-terminal"><a href="14.11.htm#conditional-or-expression">conditional-or-expression</a></span> <span class="terminal">?</span> <span class="non-terminal"><a href="14.14.htm#expression">expression</a></span> <span class="terminal">:</span> <span class="non-terminal"><a href="14.14.htm#expression">expression</a></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 conditional expression of the form b ? x : y first evaluates the condition b.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>Then, if b is true, x is evaluated and becomes the result of the operation.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>Otherwise, y is evaluated and becomes the result of the operation.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a>A conditional expression never evaluates both x and y.</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 conditional operator is right-associative, meaning that operations are grouped from right to left.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>For example, an expression of the form a ? b : c ? d : e is evaluated as a ? b : (c ? d : e).</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>The first operand of the ?: operator must be an expression of a type that can be implicitly converted to <span class="keyword">bool</span>, or an expression of a type that implements operator true.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>If neither of these requirements is satisfied, a compile-time error occurs.</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>The second and third operands of the ?: operator control the type of the conditional expression.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>Let X and Y be the types of the second and third operands.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>Then, </span><ul><li><span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a> If X and Y are the same type, then this is the type of the conditional expression.</span> </li><li><span class="sentence"><span class="sentence-number">5</span> <a name="P5S5"></a> Otherwise, if an implicit conversion (<a href="13.1.htm">§13.1</a>) exists from X to Y, but not from Y to X, then Y is the type of the conditional expression.</span> </li><li><span class="sentence"><span class="sentence-number">6</span> <a name="P5S6"></a> Otherwise, if an implicit conversion (<a href="13.1.htm">§13.1</a>) exists from Y to X, but not from X to Y, then X is the type of the conditional expression.</span> </li><li><span class="sentence"><span class="sentence-number">7</span> <a name="P5S7"></a> Otherwise, no expression type can be determined, and a compile-time error occurs.</span> </li></ul></span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>The run-time processing of a conditional expression of the form b ? x : y consists of the following steps: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P6S2"></a> First, b is evaluated, and the <span class="keyword">bool</span> value of b is determined: </span></li><ul><li><span class="sentence"><span class="sentence-number">3</span> <a name="P6S3"></a> If an implicit conversion from the type of b to <span class="keyword">bool</span> exists, then this implicit conversion is performed to produce a <span class="keyword">bool</span> value.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P6S4"></a> Otherwise, the operator true defined by the type of b is invoked to produce a <span class="keyword">bool</span> value.</span> </li></ul><li><span class="sentence"><span class="sentence-number">5</span> <a name="P6S5"></a> If the <span class="keyword">bool</span> value produced by the step above is true, then x is evaluated and converted to the type of the conditional expression, and this becomes the result of the conditional expression.</span> </li><li><span class="sentence"><span class="sentence-number">6</span> <a name="P6S6"></a> Otherwise, y is evaluated and converted to the type of the conditional expression, and this becomes the result of the conditional expression.</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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