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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="18.4.1.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="19.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="18.3.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="18.4.htm">18.4</a></span><span class="clause-title-previous"> Struct examples</span></span><span class="clause-depth"><a href="18.4.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="18.4.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">18.4.2</span><span class="clause-title"> Database boolean type</span></span><span class="informative"><span class="paragraph">The DBBool struct below implements a three-valued logical type. The possible values of this type are DBBool.True, DBBool.False, and DBBool.Null, where the Null member indicates an unknown value. Such three-valued logical types are commonly used in databases. <pre class="code-example">
using System;
public struct DBBool
{
// The three possible DBBool values.
public static readonly DBBool Null = new DBBool(0);
public static readonly DBBool False = new DBBool(-1);
public static readonly DBBool True = new DBBool(1);
// Private field that stores -1, 0, 1 for False, Null, True.
sbyte value;
// Private instance constructor. The value parameter must be -1, 0, or 1.
DBBool(int value) {
this.value = (sbyte)value;
}
// Properties to examine the value of a DBBool. Return true if this
// DBBool has the given value, false otherwise.
public bool IsNull { get { return value == 0; } }
public bool IsFalse { get { return value < 0; } }
public bool IsTrue { get { return value > 0; } }
// Implicit conversion from bool to DBBool. Maps true to DBBool.True
// and false to DBBool.False.
public static implicit operator DBBool(bool x) {
return x? True: False;
}
// Explicit conversion from DBBool to bool. Throws an exception if the
// given DBBool is Null, otherwise returns true or false.
public static explicit operator bool(DBBool x) {
if (x.value == 0) throw new InvalidOperationException();
return x.value > 0;
}
// Equality operator. Returns Null if either operand is Null,
// otherwise returns True or False.
public static DBBool operator ==(DBBool x, DBBool y) {
if (x.value == 0 || y.value == 0) return Null;
return x.value == y.value? True: False;
}
// Inequality operator. Returns Null if either operand is Null,
// otherwise returns True or False.
public static DBBool operator !=(DBBool x, DBBool y) {
if (x.value == 0 || y.value == 0) return Null;
return x.value != y.value? True: False;
}
// Logical negation operator. Returns True if the operand is False,
// Null if the operand is Null, or False if the operand is True.
public static DBBool operator !(DBBool x) {
return new DBBool(-x.value);
}
// Logical AND operator. Returns False if either operand is False,
// otherwise Null if either operand is Null, otherwise True.
public static DBBool operator &(DBBool x, DBBool y) {
return new DBBool(x.value < y.value? x.value: y.value);
}
// Logical OR operator. Returns True if either operand is True,
// otherwise Null if either operand is Null, otherwise False.
public static DBBool operator |(DBBool x, DBBool y) {
return new DBBool(x.value > y.value? x.value: y.value);
}
// Definitely true operator. Returns true if the operand is True,
// false otherwise.
public static bool operator true(DBBool x) {
return x.value > 0;
}
// Definitely false operator. Returns true if the operand is False,
// false otherwise.
public static bool operator false(DBBool x) {
return x.value < 0;
}
}
</pre></span><span class="paragraph">End of informative text. </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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