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8.1 System.String类
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C#高级编程（第3版）【全文连载】
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8.1 System.String类
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2006-10-13 14:41:00
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<h1 id="divCurrentNode" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165353.htm'><font color='red'>8.1 System.String类</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165350.htm'>7.3.1 指针(3)</a></div><div style='float:right;width:49%'>·<a href='100165351.htm'>7.3.2 使用指针优化性能</a></div><div style='float:left;width:49%'>·<a href='100165352.htm'>7.4 小结</a></div><div style='float:right;width:49%'>·<a href='100165354.htm'>8.1.1 创建字符串</a></div><div style='float:left;width:49%'>·<a href='100165355.htm'>8.1.2 格式化字符串</a></div><div style='float:right;width:49%'>·<a href='100165356.htm'>8.2 正则表达式</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><p class="MsoNormal" style="LINE-HEIGHT: 16pt"><a ftel="baseclasses"></a><a ftel="strings"><span style="FONT-FAMILY: 宋体">在本书的第一部分，我们一直在使用字符串，并说明</span><span lang="EN-US">C#</span></a><span style="FONT-FAMILY: 宋体">中</span><span lang="EN-US">string</span><span style="FONT-FAMILY: 宋体">关键字的映射实际上指向</span><span lang="EN-US">.NET </span><span style="FONT-FAMILY: 宋体">基类</span><span lang="EN-US">System.String</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">System.String</span><span style="FONT-FAMILY: 宋体">是一个功能非常强大且用途非常广泛的基类，但它不是</span><span lang="EN-US">.NET</span><span style="FONT-FAMILY: 宋体">中惟一与字符串相关的类。本章首先复习一下</span><span lang="EN-US">System.String</span><span style="FONT-FAMILY: 宋体">的特性，再介绍如何使用其他的</span><span lang="EN-US">.NET</span><span style="FONT-FAMILY: 宋体">类来处理字符串，特别是</span><span lang="EN-US">System.Text </span><span style="FONT-FAMILY: 宋体">和</span> <span lang="EN-US" style="LETTER-SPACING: -0.2pt">System.Text.RegularExpressions</span><span style="FONT-FAMILY: 宋体">命名空间中的类。本章主要介绍下述内容：</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt "Times New Roman""> </span></span><span style="FONT-FAMILY: 宋体">创建字符串：如果多次修改一个字符串，例如，在显示字符串或将其传递给其他方法或应用程序前，创建一个较长的字符串，</span><span lang="EN-US">String</span><span style="FONT-FAMILY: 宋体">类就会变得效率低下。对于这种情况，应使用另一个类</span><span lang="EN-US">System.Text.StringBuilder</span><span style="FONT-FAMILY: 宋体">，因为它是专门为这种情况设计的。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt "Times New Roman""> </span></span><span style="FONT-FAMILY: 宋体">格式化表达式：这些表达式将用于后面几章中的</span><span lang="EN-US">Console.WriteLine() </span><span style="FONT-FAMILY: 宋体">方法。格式化表达式使用两个有效的接口</span><span lang="EN-US">IFormatProvider</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">IFormattable</span><span style="FONT-FAMILY: 宋体">来处理。在自己的类上执行这两个接口，就可以定义自己的格式化序列，这样，</span><span lang="EN-US">Console.WriteLine()</span><span style="FONT-FAMILY: 宋体">和类似的类就可以以指定的方式显示类的值。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt "Times New Roman""> </span></span><span style="FONT-FAMILY: 宋体">正则表<span style="LETTER-SPACING: -0.15pt">达式：</span></span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">.NET</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">还提供了一些非常复杂的类来识别字符串，或从长字符串中提取满足某些比较复杂条件的子字符串。例如，找出字符串中重复出现的某个字符或一组字符，或者找出以</span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">s</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">开头、且至少包含一个</span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">n</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">的所有单词，或者找出遵循雇员</span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">ID</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">或社会安全号码约定的字符串。虽然可以使用字符串类，编写方法来执行这类处理，但这类方法编写起来比较繁琐，而使用</span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">System.Text.RegularExpressions</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">命名空间中的类就比较简单，</span><span lang="EN-US" style="LETTER-SPACING: -0.15pt">System.Text.RegularExpressions</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.15pt">专门用于执行这类处</span><span style="FONT-FAMILY: 宋体">理。</span></p>
<h3 style="MARGIN-TOP: 11.4pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 11.4pt"><a ftel="_Toc507815064"><span lang="EN-US">8.1 System.String</span></a><span style="FONT-FAMILY: 楷体_GB2312">类</span></h3>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><a ftel="String1"><span style="FONT-FAMILY: 宋体">在介绍其他字符串类之前，先快速复习一下</span><span lang="EN-US">String</span></a><span style="FONT-FAMILY: 宋体">类上一些可利用的方法。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><span lang="EN-US">System.String</span><span style="FONT-FAMILY: 宋体">是一个类，该类专门用于存储字符串，允许对字符串进行许多操作。由于这种数据类型非常重要，</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">提供了它自己的关键字和相关的语法，以便使用这个类来很容易地处理字符串。</span></p>
<p class="MsoToc1" style="LINE-HEIGHT: 16pt"><span style="FONT-FAMILY: 宋体">使用运算符重载可以连接字符串：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">string message1 = "Hello"; //return "Hello"</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">message1 += ", There"; // return "Hello, There "</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">string message2 = message1 + "!"; // return "Hello, There!"</span></p>
<p class="MsoNormal"><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">还允许使用类似于索引符的语法来提取指定的字符：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">char char4 = "message" [4]; // returns 'a'. Note the char is zero-indexed</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这个类可以完成许多常见的任务，例如替换字符、删除空白和把字母变成大写形式等。可用的方法如表</span><span lang="EN-US">8-1</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p class="a5" style="MARGIN-TOP: 4.9pt"><a ftel="Stringmethods"><span style="FONT-FAMILY: 黑体">表</span><span lang="EN-US"> 8-1</span></a></p>
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<p class="a2"><span style="FONT-FAMILY: 黑体">方</span><span lang="EN-US" style="FONT-FAMILY: "Times New Roman""> </span><span style="FONT-FAMILY: 黑体">法</span></p>
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<p class="a2"><span style="FONT-FAMILY: 黑体">作</span><span lang="EN-US" style="FONT-FAMILY: "Times New Roman""> </span><span style="FONT-FAMILY: 黑体">用</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">Compare</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">比较字符串的内容，考虑文化背景</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">场所</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，确定某些字符是否相等</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">CompareOrdinal</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">与</span><span lang="EN-US">Compare</span><span style="FONT-FAMILY: 宋体">一样，但不考虑文化背景</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">Format</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">格式化包含各种值的字符串和如何格式化每个值的说明符</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">IndexOf</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">定位字符串中第一次出现某个给定子字符串或字符的位置</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">IndexOfAny</span></p>
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<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">定位字符串中第一次出现某个字符或一组字符的位置</span></p>
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