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30.3.1 流
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30.3.1 流
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165768.htm'>30.1.3 示例：文件浏览器</a></div><div style='float:right;width:49%'>·<a href='100165769.htm'>30.2 移动、复制和删除文件</a></div><div style='float:left;width:49%'>·<a href='100165770.htm'>30.3 读写文件</a></div><div style='float:right;width:49%'>·<a href='100165772.htm'>30.3.2 读写二进制文件</a></div><div style='float:left;width:49%'>·<a href='100165773.htm'>30.3.3 读写文本文件</a></div><div style='float:right;width:49%'>·<a href='100165774.htm'>30.4 读写注册表</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style='margin-top:8.15pt;margin-right:0cm;FTEL:8.15pt;margin-left:
0cm'><a FTEL="_Toc507815211"><span lang=EN-US>30.3.1 </span></a><span
style='font-family:黑体'>流</span></h3>
<p class=MsoNormal style='line-height:15.0pt'><span style='font-family:宋体'>流的概念已经存在很长时间了。流是一个用于传输数据的对象，数据的传输有两个方向：</span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US>●<span
style='font:7.0pt "Times New Roman"'> </span></span><span
style='font-family:宋体'>如果数据从外部源传输到程序中，这就是读取流。</span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US>●<span
style='font:7.0pt "Times New Roman"'> </span></span><span
style='font-family:宋体'>如果数据从程序传输到外部源，这就是写入流。</span></p>
<p class=MsoNormal style='line-height:15.0pt'><span style='font-family:宋体'>外部源常常是一个文件，但也不完全都是文件。它还可能是：</span></p>
<p class=1 style='margin-left:36.95pt;FTEL:-15.5pt'><span lang=EN-US
style='letter-spacing:-.2pt'>●<span style='font:7.0pt "Times New Roman"'>
</span></span><span style='font-family:宋体;letter-spacing:-.2pt'>使用一些网络协议读写网络上的数据，其目的是选择数据，或从另一个计算机上发送数据。</span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US>●<span
style='font:7.0pt "Times New Roman"'> </span></span><span
style='font-family:宋体'>读写到指定的管道上。</span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US>●<span
style='font:7.0pt "Times New Roman"'> </span></span><span
style='font-family:宋体'>把数据读写到一个内存区域上。</span></p>
<p class=MsoNormal style='line-height:15.0pt'><span style='font-family:宋体'>在这些示例中，</span><span
lang=EN-US>Microsoft</span><span style='font-family:宋体'>提供了一个</span><span
lang=EN-US>.NET</span><span style='font-family:宋体'>基类</span><span lang=EN-US>System.IO.MemoryStream</span><span
style='font-family:宋体'>来读写内存，而</span><span lang=EN-US>System.Net.Sockets.NetworkStream</span><span
style='font-family:宋体'>则处理网络数据。读写管道没有基本的流类，但有一个常见的流类</span><span lang=EN-US>System.IO.Stream</span><span
style='font-family:宋体'>，如果要编写一个这样的类，可以从这个基类继承。流对外部数据源不做任何假定。</span></p>
<p class=MsoNormal style='line-height:15.0pt'><span style='font-family:宋体'>外部源甚至可以是代码中的一个变量。这听起来很荒谬，但使用流在变量之间传输数据的技术是一个非常有用的技巧，可以在数据类型之间转换数据。</span><span
lang=EN-US>C</span><span style='font-family:宋体'>语言使用它在整型和字符串之间转换数据类型，或者使用函数</span><span
lang=EN-US>sprintf()</span><span style='font-family:宋体'>格式化字符串。</span></p>
<p class=MsoNormal style='line-height:15.0pt'><span style='font-family:宋体'>使用一个独立的对象来传输数据，比使用</span><span
lang=EN-US>FileInfo</span><span style='font-family:宋体'>或</span><span
lang=EN-US>DirectoryInfo</span><span style='font-family:宋体'>类更好，因为把传输数据的概念与特定数据源分离开来，可以更容易切换数据源。流对象本身包含许多代码，可以在外部数据源和代码中的变量之间移动数据，把这些代码与特定数据源的概念分离开来，就更容易实现不同环境下代码的重使用</span><span
lang=EN-US>(</span><span style='font-family:宋体'>通过继承</span><span lang=EN-US>)</span><span
style='font-family:宋体'>。例如，前面提到的</span><span lang=EN-US>StringReader </span><span
style='font-family:宋体'>和</span><span lang=EN-US> StringWriter</span><span
style='font-family:宋体'>类，与本章后面用于读写文本文件的两个类</span><span lang=EN-US>StreamReader </span><span
style='font-family:宋体'>和</span><span lang=EN-US> StreamWriter</span><span
style='font-family:宋体'>一样，都是同一继承树上的一部分，这些类在后台共享许多代码。</span></p>
<p class=MsoNormal style='FTEL:3.25pt;line-height:15.0pt'><span
style='font-family:宋体'>在</span><span lang=EN-US>System.IO</span><span
style='font-family:宋体'>命名空间中，与流相关的类层次结构如图</span><span lang=EN-US>30-6</span><span
style='font-family:宋体'>所示。</span></p>
<p align=center><span lang=EN-US><img width=300 height=216
src="30/image007.jpg"></span></p>
<p align=center style='FTEL:8.15pt'><span style='font-family:宋体'>图</span><span
lang=EN-US> 30-6</span></p>
<p class=MsoNormal><span style='font-family:宋体'>对于文件的读写，最常用的类如下：</span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US>●<span
style='font:7.0pt "Times New Roman"'> </span></span><span lang=EN-US>FileStream(</span><span style='font-family:宋体'>文件流</span><span
lang=EN-US>)</span><span style='font-family:宋体'>：这个类主要用于在任何二进制文件中读写二进制数据<span
style='letter-spacing:-1.0pt'>——</span></span><span style='letter-spacing:-1.0pt'>
</span><span style='font-family:宋体'>也可以使用它读写任何文件。</span><span lang=EN-US> </span></p>
<p class=1 style='margin-left:37.55pt;FTEL:-16.1pt'><span lang=EN-US
style='letter-spacing:-.1pt'>●<span style='font:7.0pt "Times New Roman"'>
</span></span><span
lang=EN-US style='letter-spacing:-.1pt'>StreamReader(</span><span
style='font-family:宋体;letter-spacing:-.1pt'>流读取器</span><span lang=EN-US
style='letter-spacing:-.1pt'>)</span><span style='font-family:宋体;letter-spacing:
-.1pt'>和</span><span
lang=EN-US style='letter-spacing:-.1pt'>StreamWriter(</span><span
style='font-family:宋体;letter-spacing:-.1pt'>流写入器</span><span lang=EN-US
style='letter-spacing:-.1pt'>)</span><span style='font-family:宋体;letter-spacing:
-.1pt'>：这两个类是专门用于读写文本文</span><span lang=EN-US style='letter-spacing:-.1pt'>
</span><span style='font-family:宋体;letter-spacing:-.1pt'>件的。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>虽然我们没有在示例中使用另外两个类</span><span
lang=EN-US>BinaryReader </span><span style='font-family:宋体'>和</span> <span lang=EN-US>BinaryWriter</span><span style='font-family:宋体'>，但它们也是很有用的。</span><span
lang=EN-US>BinaryReader </span><span style='font-family:宋体'>和</span> <span lang=EN-US>BinaryWriter</span><span style='font-family:宋体'>这两个类本身并不执行流，而是提供其他流对象的包装。</span><span
lang=EN-US>BinaryReader </span><span style='font-family:宋体'>和</span> <span lang=EN-US>BinaryWriter</span><span style='font-family:宋体'>还可以对二进制数据进行额外的格式化，直接从相关的流中读写</span><span
lang=EN-US>C#</span><span style='font-family:宋体'>变量的内容。最简单的方式是把</span><span
lang=EN-US>BinaryReader </span><span style='font-family:宋体'>和</span> <span lang=EN-US>BinaryWriter</span><span style='font-family:宋体'>放在流和代码之间，进行额外的格式化，如图</span><span
lang=EN-US>30-7</span><span style='font-family:宋体'>所示。</span></p>
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<p class=MsoNormal style='FTEL:0cm;line-height:12.0pt'><span
lang=EN-US style='font-size:7.5pt'>BinaryWriter</span></p>
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