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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="18.3.7.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="18.3.9.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="17.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="19.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="18.htm">18</a></span><span class="clause-title-previous"> Structs</span></span><span class="clause-depth"><a href="18.2.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="18.4.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="18.3.htm">18.3</a></span><span class="clause-title-previous"> Class and struct differences</span></span><span class="clause-depth"><a href="18.3.7.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="18.3.9.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">18.3.8</span><span class="clause-title"> Constructors</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>Unlike a class, a struct is not permitted to declare a parameterless instance constructor.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>Instead, every struct implicitly has a parameterless instance constructor, which always returns the value that results from setting all value type fields to their default value and all reference type fields to null (<a href="11.1.1.htm">§11.1.1</a>).</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a>A struct can declare instance constructors having parameters.</span> <span class="example">[Example: For example <pre class="code-example">
struct Point
{
int x, y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
}
</pre></span></span><span class="paragraph"><span class="example">Given the above declaration, the statements <pre class="code-example">
Point p1 = new Point();
Point p2 = new Point(0, 0);
</pre>both create a Point with x and y initialized to zero. end example]</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 struct instance constructor is not permitted to include a constructor initializer of the form base(...).</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 this variable of a struct instance constructor corresponds to an out parameter of the struct type, and similar to an out parameter, this must be definitely assigned (<a href="12.3.htm">§12.3</a>) at every location where the constructor returns.</span> <span class="example">[Example: Consider the instance constructor implementation below: <pre class="code-example">
struct Point
{
int x, y;
public int X {
set { x = value; }
}
public int Y {
set { y = value; }
}
public Point(int x, int y) {
X = x; // error, this is not yet definitely assigned
Y = y; // error, this is not yet definitely assigned
}
}
</pre></span></span><span class="paragraph"><span class="example">No instance member function (including the set accessors for the properties X and Y) can be called until all fields of the struct being constructed have been definitely assigned. Note, however, that if Point were a class instead of a struct, the instance constructor implementation would be permitted. 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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