FileInfo.OpenRead Method

Reference

Definition

Namespace:: System.IO

Assemblies:: mscorlib.dll, System.IO.FileSystem.dll

Assemblies:: netstandard.dll, System.Runtime.dll

Assemblies:: netstandard.dll, System.IO.FileSystem.dll

Assemblies:: netstandard.dll, System.IO.FileSystem.dll, System.Runtime.dll

Assembly:: System.IO.FileSystem.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Source:: FileInfo.cs

Source:: FileInfo.cs

Source:: FileInfo.cs

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Creates a read-only FileStream.

public:
 System::IO::FileStream ^ OpenRead();

public System.IO.FileStream OpenRead();

member this.OpenRead : unit -> System.IO.FileStream

Public Function OpenRead () As FileStream

Returns

FileStream

A new read-only FileStream object.

Exceptions

UnauthorizedAccessException

Name is read-only or is a directory.

DirectoryNotFoundException

The specified path is invalid, such as being on an unmapped drive.

IOException

The file is already open.

Examples

The following example opens a file as read-only and reads from it.

using namespace System;
using namespace System::IO;
using namespace System::Text;

int main()
{
   String^ path = "c:\\MyTest.txt";
   FileInfo^ fi = gcnew FileInfo( path );
   
   // Delete the file if it exists.
   if (  !fi->Exists )
   {
      //Create the file.
      FileStream^ fs = fi->Create();
      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.
   FileStream^ fs = fi->OpenRead();
   try
   {
      array<Byte>^b = gcnew array<Byte>(1024);
      UTF8Encoding^ temp = gcnew UTF8Encoding( true );
      while ( fs->Read( b, 0, b->Length ) > 0 )
      {
         Console::WriteLine( temp->GetString( b ) );
      }
   }
   finally
   {
      if ( fs )
         delete (IDisposable^)fs;
   }
}
//This code produces output similar to the following; 
//results may vary based on the computer/file structure/etc.:
//
//This is some text in the file.
//
//
//
//
//
//
//
//
//
//
//
//
//

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

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

        // Delete the file if it exists.
        if (!fi.Exists)
        {
            //Create the file.
            using (FileStream fs = fi.Create())
            {
                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 (FileStream fs = fi.OpenRead())
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b,0,b.Length) > 0)
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}
//This code produces output similar to the following;
//results may vary based on the computer/file structure/etc.:
//
//This is some text in the file.
//
//
//
//
//
//
//
//
//
//
//
//

Imports System.IO
Imports System.Text

Public Class Test

    Public Shared Sub Main()
        Dim path As String = "c:\temp\MyTest.txt"
        Dim fi As FileInfo = New FileInfo(path)
        Dim fs As FileStream

        ' Delete the file if it exists.
        If fi.Exists = False Then
            'Create the file.
            fs = fi.Create()
            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)
            fs.Close()
        End If

        'Open the stream and read it back.
        fs = fi.OpenRead()
        Dim b(1023) As Byte
        Dim temp As UTF8Encoding = New UTF8Encoding(True)

        Do While fs.Read(b, 0, b.Length) > 0
            Console.WriteLine(temp.GetString(b))
        Loop
        fs.Close()
    End Sub
End Class
'This code produces output similar to the following; 
'results may vary based on the computer/file structure/etc.:
'
'This is some text in the file.
'
'
'
'
'
'
'
'
'
'
'
'
'

Remarks

This method returns a read-only FileStream object with the FileShare mode set to Read.

Applies to

Product	Versions
.NET	Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9, 10
.NET Framework	1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard	1.3, 1.4, 1.6, 2.0, 2.1
UWP	10.0

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