File.OpenText(String) 方法

定义

命名空间:

System.IO

程序集:

System.Runtime.dll

Source:

File.cs

打开现有 UTF-8 编码文本文件以进行读取。

public:
 static System::IO::StreamReader ^ OpenText(System::String ^ path);

public static System.IO.StreamReader OpenText (string path);

static member OpenText : string -> System.IO.StreamReader

Public Shared Function OpenText (path As String) As StreamReader

参数

path

String

要打开以进行读取的文件。

返回

StreamReader

指定路径上的 StreamReader。

例外

UnauthorizedAccessException

调用方没有所要求的权限。

ArgumentException

.NET Framework 和 .NET Core 版本早于 2.1： path 是零长度字符串，仅包含空格，或包含一个或多个无效字符。 你可以使用 GetInvalidPathChars() 方法查询无效字符。

ArgumentNullException

path 为 null。

PathTooLongException

指定的路径和/或文件名超过了系统定义的最大长度。

DirectoryNotFoundException

指定的路径无效（例如，它位于未映射的驱动器上）。

FileNotFoundException

未找到 path 中指定的文件。

NotSupportedException

path 的格式无效。

示例

以下示例打开一个文本文件进行读取。

using namespace System;
using namespace System::IO;
using namespace System::Text;
int main()
{
   String^ path = "c:\\temp\\MyTest.txt";
   
   if ( !File::Exists( path ) )
   {
      // Create the file.
      FileStream^ fs = File::Create( path );
      try
      {
         array<Byte>^info = (gcnew UTF8Encoding( true ))->GetBytes( "This is some text in the file." );
         
         // Add some information to the file.
         fs->Write( info, 0, info->Length );
      }
      finally
      {
         if ( fs )
            delete (IDisposable^)fs;
      }
   }
   
   // Open the stream and read it back.
   StreamReader^ sr = File::OpenText( path );
   try
   {
      String^ s = "";
      while ( s = sr->ReadLine() )
      {
         Console::WriteLine( s );
      }
   }
   finally
   {
      if ( sr )
         delete (IDisposable^)sr;
   }
}

using System;
using System.IO;
using System.Text;

class Test
{
    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";

        if (!File.Exists(path))
        {
            // Create the file.
            using (FileStream fs = File.Create(path))
            {
                Byte[] info =
                    new UTF8Encoding(true).GetBytes("This is some text in the file.");

                // Add some information to the file.
                fs.Write(info, 0, info.Length);
            }
        }

        // Open the stream and read it back.
        using (StreamReader sr = File.OpenText(path))
        {
            string s = "";
            while ((s = sr.ReadLine()) != null)
            {
                Console.WriteLine(s);
            }
        }
    }
}

open System.IO
open System.Text

let path = @"c:\temp\MyTest.txt"

if File.Exists path |> not then
    // Create the file.
    use fs = File.Create path

    let info =
        UTF8Encoding(true)
            .GetBytes "This is some text in the file."

    // Add some information to the file.
    fs.Write(info, 0, info.Length)

// Open the stream and read it back.
do
    use sr = File.OpenText path
    let mutable s = sr.ReadLine()

    while isNull s |> not do
        printfn $"{s}"
        s <- sr.ReadLine()

Imports System.IO
Imports System.Text

Public Class Test
  Public Shared Sub Main()
    Dim path As String = "c:\temp\MyTest.txt"

    If Not File.Exists(path) Then
      ' Create the file.
      Using fs As FileStream = File.Create(path)
        Dim info As Byte() = _
         New UTF8Encoding(True).GetBytes("This is some text in the file.")

        ' Add some information to the file.
        fs.Write(info, 0, info.Length)
      End Using
    End If

    ' Open the stream and read it back. 
    Using sr As StreamReader = File.OpenText(path)
      Do While sr.Peek() >= 0
        Console.WriteLine(sr.ReadLine())
      Loop
    End Using

  End Sub
End Class

注解

此方法等效于 StreamReader(String) 构造函数重载。

允许 path 参数指定相对路径信息或绝对路径信息。 相对路径信息被解释为相对于当前工作目录。 若要获取当前工作目录，请参阅 GetCurrentDirectory。

有关常见 I/O 任务的列表，请参阅 常见 I/O 任务。

另请参阅

• 文件和流 I/O
• 从文件读取文本
• 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