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<p class="a1" style="MARGIN-BOTTOM: 8.15pt; TEXT-INDENT: 21.45pt"><span style="FONT-FAMILY: 楷体_GB2312">“兼容”是指对象是该类型，或者派生于该类型。</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">int i = 10;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">if (i is object)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("i is an object");</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span lang="EN-US" style="LETTER-SPACING: -0.1pt">int</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">和从</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">object</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">继承而来的其他</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">C#</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">数据类型一样，表达式</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">i is object</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">将得到</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">true</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">，并显示信息。</span></p>
<h3 style="MARGIN: 8.15pt 0cm"><span lang="EN-GB">5.1.5 a</span><span lang="EN-GB">s</span><span style="FONT-FAMILY: 黑体">运算符</span></h3>
<p class="MsoNormal"><span lang="EN-US">as</span><span style="FONT-FAMILY: 宋体">运算符用于执行引用类型的显式类型转换。如果要转换的类型与指定的类型兼容，转换就会成功进行；如果类型不兼容，</span><span lang="EN-US">as</span><span style="FONT-FAMILY: 宋体">运算符就会返回值</span><span lang="EN-US">null</span><span style="FONT-FAMILY: 宋体">。如下面的代码所示，如果</span><span lang="EN-US">object</span><span style="FONT-FAMILY: 宋体">引用不指向</span><span lang="EN-US">string</span><span style="FONT-FAMILY: 宋体">实例，把</span><span lang="EN-US">object</span><span style="FONT-FAMILY: 宋体">引用转换为</span><span lang="EN-US">string</span><span style="FONT-FAMILY: 宋体">就会返回</span><span lang="EN-US">null</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">object o1 = "Some String";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">object o2 = 5;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">string s1 = o1 as string; //s1 = "Some String"</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">string s2 = o2 as string; //s1 = null</span></p>
<p class="MsoNormal"><span lang="EN-US">as</span><span style="FONT-FAMILY: 宋体">运算符允许在一步中进行安全的类型转换，不需要先使用</span><span lang="EN-US">is</span><span style="FONT-FAMILY: 宋体">运算符测试类型，再执行</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 宋体">转换。</span></p>
<h3 style="MARGIN: 8.15pt 0cm"><span></span><span lang="EN-GB">5.1.6</span><span lang="EN-GB"> sizeof</span><span style="FONT-FAMILY: 黑体">运算符</span></h3>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">使用</span><span lang="EN-US">sizeof</span></span><span style="FONT-FAMILY: 宋体">运算符可以确定堆栈中值类型需要的长度</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">单位是字节</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">string s = "A string";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">unsafe</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine(sizeof(int));</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">其结果是显示数字</span><span lang="EN-US">4</span><span style="FONT-FAMILY: 宋体">，因为</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">有</span><span lang="EN-US">4</span><span style="FONT-FAMILY: 宋体">个字节。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意，只能在不安全代码中使用</span><span lang="EN-US">sizeof</span><span style="FONT-FAMILY: 宋体">运算符。第</span><span lang="EN-US">7</span><span style="FONT-FAMILY: 宋体">章将详细论述不安全代码。</span></p>
<h3 style="MARGIN: 8.15pt 0cm"><span><span lang="EN-GB">5.1.7 typeof</span></span><span style="FONT-FAMILY: 黑体">运算符</span></h3>
<p class="MsoNormal"><span lang="EN-US">Typeof</span><span style="FONT-FAMILY: 宋体">运算符返回一个表示特定类型的</span><span lang="EN-US">Type</span><span style="FONT-FAMILY: 宋体">对象。例如，</span><span lang="EN-US">typeof(string)</span><span style="FONT-FAMILY: 宋体">返回表示</span><span lang="EN-US">System.String</span><span style="FONT-FAMILY: 宋体">类型的</span><span lang="EN-US">Type</span><span style="FONT-FAMILY: 宋体">对象。在使用反射动态查找对象的信息时，这个运算符是很有效的。第</span><span lang="EN-US">10</span><span style="FONT-FAMILY: 宋体">章将介绍反射。</span></p>
<h3 style="MARGIN: 8.15pt 0cm"><span><span lang="EN-GB">5.1.8 </span></span><span style="FONT-FAMILY: 黑体">运算符的优先级</span></h3>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">表</span><span lang="EN-US">5-3</span></span><span style="FONT-FAMILY: 宋体">显示了</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">运算符的优先级。表顶部的运算符有最高的优先级</span><span lang="EN-GB">(</span><span style="FONT-FAMILY: 宋体">即在包含多个运算符的表达式中，最先计算该运算符</span><span lang="EN-GB">)</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="a5" style="MARGIN-TOP: 8.15pt"><span style="FONT-FAMILY: 黑体">表</span><span lang="EN-US"> 5-3</span></p>
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<p class="a2"><span style="FONT-FAMILY: 黑体">组</span></p>
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<p class="a2"><span style="FONT-FAMILY: 黑体">运</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 黑体">算</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 黑体">符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">初级运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">()</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">.</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">[]</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">x++</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">x</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -1pt">––</span> <span lang="EN-US"> new typeof sizeof checked unchecked</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">一元运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">+ </span><span style="FONT-FAMILY: 宋体">–</span><span lang="EN-US"> ! ~ ++x </span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -1pt">––</span><span lang="EN-US">x</span><span style="FONT-FAMILY: 宋体">和数据类型转换</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">乘</span><span lang="EN-US">/</span><span style="FONT-FAMILY: 宋体">除运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">* / %</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">加</span><span lang="EN-US">/</span><span style="FONT-FAMILY: 宋体">减运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">+ –</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">移位运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US"><< >></span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">关系运算符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">< > <= >= is as</span></p>
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