StreamReader 类

定义

public ref class StreamReader : System::IO::TextReader

public class StreamReader : System.IO.TextReader

[System.Serializable]
public class StreamReader : System.IO.TextReader

[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public class StreamReader : System.IO.TextReader

type StreamReader = class
    inherit TextReader

[<System.Serializable>]
type StreamReader = class
    inherit TextReader

[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type StreamReader = class
    inherit TextReader

Public Class StreamReader
Inherits TextReader

继承

Object

TextReader

StreamReader

继承

Object

MarshalByRefObject

TextReader

StreamReader

属性

SerializableAttribute ComVisibleAttribute

示例

以下示例使用 的 StreamReader 实例从文件中读取文本。 不支持在 Windows 应用商店应用中使用此示例中使用的构造函数。

using namespace System;
using namespace System::IO;
int main()
{
   try
   {
      // Create an instance of StreamReader to read from a file.
      StreamReader^ sr = gcnew StreamReader( "TestFile.txt" );
      try
      {
         String^ line;
         
         // Read and display lines from the file until the end of 
         // the file is reached.
         while ( line = sr->ReadLine() )
         {
            Console::WriteLine( line );
         }
      }
      finally
      {
         if ( sr )
            delete (IDisposable^)sr;
      }
   }
   catch ( Exception^ e ) 
   {
      // Let the user know what went wrong.
      Console::WriteLine( "The file could not be read:" );
      Console::WriteLine( e->Message );
   }
}

using System;
using System.IO;

class Test
{
    public static void Main()
    {
        try
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader("TestFile.txt"))
            {
                string line;
                // Read and display lines from the file until the end of
                // the file is reached.
                while ((line = sr.ReadLine()) != null)
                {
                    Console.WriteLine(line);
                }
            }
        }
        catch (Exception e)
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

Imports System.IO

Class Test
    Public Shared Sub Main()
        Try
            ' Create an instance of StreamReader to read from a file.
            Dim sr As StreamReader = New StreamReader("TestFile.txt")
            Dim line As String
            ' Read and display the lines from the file until the end 
            ' of the file is reached.
            Do
                line = sr.ReadLine()
                Console.WriteLine(Line)
            Loop Until line Is Nothing
            sr.Close()
        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
    End Sub
End Class

以下示例实例化 一个 StreamReader 对象，并调用其 ReadAsync 方法以异步方式读取文件。

using System;
using System.IO;
using System.Threading.Tasks;

class Example
{
    static async Task Main()
    {
        await ReadAndDisplayFilesAsync();
    }

    static async Task ReadAndDisplayFilesAsync()
    {
        String filename = "TestFile1.txt";
        Char[] buffer;

        using (var sr = new StreamReader(filename)) {
            buffer = new Char[(int)sr.BaseStream.Length];
            await sr.ReadAsync(buffer, 0, (int)sr.BaseStream.Length);
        }

        Console.WriteLine(new String(buffer));
    }
}
// The example displays the following output:
//       This is the first line of text in a relatively short file.
//       This is the second line.
//       This is the third line.
//       This is the fourth and final line.

Imports System.IO
Imports System.Threading.Tasks

Module Example
    Public Sub Main()
        ReadAndDisplayFilesAsync()
    End Sub

    Private Async Sub ReadAndDisplayFilesAsync()
        Dim filename As String = "TestFile1.txt"
        Dim buffer() As Char
        
        Using sr As New StreamReader(filename)
            ReDim buffer(CInt(sr.BaseStream.Length))
            Await sr.ReadAsync(buffer, 0, CInt(sr.BaseStream.Length))
        End Using

        Console.WriteLine(New String(buffer))
    End Sub
End Module
' The example displays the following output:
'       This is the first line of text in a relatively short file.
'       This is the second line.
'       This is the third line.
'       This is the fourth and final line.

注解

StreamReader 专为特定编码中的字符输入而设计，而 Stream 类专为字节输入和输出而设计。 用于 StreamReader 从标准文本文件中读取信息行。

StreamReader 除非另有指定，否则默认为 UTF-8 编码，而不是默认为当前系统的 ANSI 代码页。 UTF-8 正确处理 Unicode 字符，并在操作系统的本地化版本上提供一致的结果。 如果使用 属性获取当前字符编码 CurrentEncoding ，则值在第一个 Read 方法之后才可靠，因为编码自动检测直到第一 Read 次调用方法才完成。

默认情况下， StreamReader 不是线程安全的。 有关线程安全包装器，请参阅 TextReader.Synchronized 。

Read(Char[], Int32, Int32)和 Write(Char[], Int32, Int32) 方法重载参数指定的count字符数的读取和写入。 它们与 和 BufferedStream.Write区分开BufferedStream.Read来，后者读取和写入 参数指定的count字节数。 BufferedStream方法仅用于读取和写入字节数组元素的整数数。

有关常见 I/O 任务的列表，请参阅 常见 I/O 任务。

构造函数

字段

属性

方法

显式接口实现

适用于

另请参阅

• Encoding
• Stream
• StreamWriter
• 文件和流 I/O
• 如何：从文件中读取文本
• 如何：将文本写入文件
• 如何：对新建的数据文件进行读取和写入