VB.Net - 从文本文件读取和写入

由 youj 创建, 最后一次修改 2016-12-16

StreamReader和StreamWriter类用于从文本文件读取和写入数据。 这些类继承自抽象基类Stream,它支持将字节读取和写入文件流。


StreamReader类

StreamReader类还继承自抽象基类TextReader,它代表用于阅读一系列字符的读者。 下表描述了StreamReader类的一些常用方法:


S.N方法名称和用途
1

Public Overrides Sub Close

It closes the StreamReader object and the underlying stream and releases any system resources associated with the reader.

它关闭StreamReader对象和基础流,并释放与读取器相关联的任何系统资源。

2

Public Overrides Function Peek As Integer

Returns the next available character but does not consume it.

返回下一个可用字符,但不使用它。

3

Public Overrides Function Read As Integer

Reads the next character from the input stream and advances the character position by one character.

从输入流中读取下一个字符,并将字符位置前移一个字符。


示例:

以下示例演示读取名为Jamaica.txt的文本文件。 该文件读为:
Down the way where the nights are gay
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop
Imports System.IO
Module fileProg
   Sub Main()
      Try
          ' Create an instance of StreamReader to read from a file. 
          ' The using statement also closes the StreamReader. 
          Using sr As StreamReader = New StreamReader("e:/jamaica.txt")
              Dim line As String
              ' Read and display lines from the file until the end of  
              ' the file is reached. 
              line = sr.ReadLine()
              While (line <> Nothing)
                  Console.WriteLine(line)
                  line = sr.ReadLine()
              End While
          End Using
      Catch e As Exception
          ' Let the user know what went wrong.
          Console.WriteLine("The file could not be read:")
          Console.WriteLine(e.Message)
      End Try
      Console.ReadKey()
   End Sub
End Module
猜测当你编译和运行程序时显示什么?

StreamWriter类

StreamWriter类继承自抽象类TextWriter,表示一个写入器,它可以写一系列字符。

下表显示了此类最常用的一些方法:
S.N方法名称和用途
1Public Overrides Sub Close 
Closes the current StreamWriter object and the underlying stream.
关闭当前StreamWriter对象和基础流。
2

Public Overrides Sub Flush

Clears all buffers for the current writer and causes any buffered data to be written to the underlying stream.

清除当前写入程序的所有缓冲区,并使任何缓冲的数据写入基础流。

3

Public Overridable Sub Write (value As Boolean)

Writes the text representation of a Boolean value to the text string or stream. (Inherited from TextWriter.)

将布尔值的文本表示写入文本字符串或流。(从TextWriter继承。)

4

Public Overrides Sub Write (value As Char)

Writes a character to the stream.

将字符写入流。

5

Public Overridable Sub Write (value As Decimal)

Writes the text representation of a decimal value to the text string or stream.

将十进制值的文本表示写入文本字符串或流。

6

Public Overridable Sub Write (value As Double)

Writes the text representation of an 8-byte floating-point value to the text string or stream.

将8字节浮点值的文本表示写入文本字符串或流。

7

Public Overridable Sub Write (value As Integer)

Writes the text representation of a 4-byte signed integer to the text string or stream.

将4字节有符号整数的文本表示写入文本字符串或流。

8

Public Overrides Sub Write (value As String)

Writes a string to the stream.

将字符串写入流。

9

Public Overridable Sub WriteLine

Writes a line terminator to the text string or stream.

将行终止符写入文本字符串或流。

以上列表并不详尽。 有关方法的完整列表,请访问Microsoft的文档。

示例:

以下示例演示使用StreamWriter类将文本数据写入文件:
Imports System.IO
Module fileProg
   Sub Main()
      Dim names As String() = New String() {"Zara Ali", _
         "Nuha Ali", "Amir Sohel", "M Amlan"}
      Dim s As String
      Using sw As StreamWriter = New StreamWriter("names.txt")
          For Each s In names
              sw.WriteLine(s)
          Next s
      End Using
      ' Read and show each line from the file. 
      Dim line As String
      Using sr As StreamReader = New StreamReader("names.txt")
          line = sr.ReadLine()
          While (line <> Nothing)
              Console.WriteLine(line)
              line = sr.ReadLine()
          End While
      End Using
      Console.ReadKey()
   End Sub
End Module

当上述代码被编译和执行时,它产生以下结果:
Zara Ali
Nuha Ali
Amir Sohel
M Amlan 

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