File.OpenText(String) 方法

定義

命名空間:

System.IO

組件:

System.Runtime.dll

來源:

File.cs

開啟現有 UTF-8 編碼的文字檔來讀取。

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

參數

path

String

要被開啟來讀取的檔案。

傳回

StreamReader

指定路徑上的 StreamReader。

例外狀況

UnauthorizedAccessException

呼叫端沒有必要的權限。

ArgumentException

.NET Framework和 2.1 之前的 .NET Core 版本： path 是長度為零的字串、只包含空白字元，或包含一或多個無效字元。 您可以使用 GetInvalidPathChars() 方法查詢無效字元。

ArgumentNullException

path 為 null。

PathTooLongException

指定的路徑、檔案名稱，或兩者都超出系統定義的長度上限。

DirectoryNotFoundException

指定的路徑無效 (例如，它位於未對應的磁碟機上)。

FileNotFoundException

找不到 path 指定的檔案。

NotSupportedException

path 格式無效。

範例

下列範例會開啟文字檔以供讀取。

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

備註

這個方法相當於建 StreamReader(String) 構函式多載。

允許 path 參數指定相對路徑或絕對路徑資訊。 相對路徑資訊會解譯為相對於目前的工作目錄。 若要取得目前的工作目錄，請參閱 GetCurrentDirectory 。

如需一般 I/O 工作的清單，請參閱 一般 I/O 工作。

另請參閱

• 檔案和資料流程 I/O
• 從檔案讀取文字
• 作法：將文字寫入檔案
• 作法：讀取和寫入新建立的資料檔案