File.OpenRead Method (System.IO)

OpenRead Method

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This page is specific to

Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

File..::.OpenRead Method

Updated: November 2007

Opens an existing file for reading.

Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)

Syntax

Visual Basic (Declaration)

Public Shared Function OpenRead ( _
    path As String _
) As FileStream

Visual Basic (Usage)

Dim path As String
Dim returnValue As FileStream

returnValue = File.OpenRead(path)

public static FileStream OpenRead(
    string path
)

Visual C++

public:
static FileStream^ OpenRead(
    String^ path
)

public static FileStream OpenRead(
    String path
)

JScript

public static function OpenRead(
    path : String
) : FileStream

Parameters

path: Type: System..::.String
The file to be opened for reading.

Return Value

Type: System.IO..::.FileStream

A read-only FileStream on the specified path.

Exceptions

Exception	Condition
ArgumentException	path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by InvalidPathChars.
ArgumentNullException	path is nullNothingnullptra null reference (Nothing in Visual Basic).
PathTooLongException	The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.
DirectoryNotFoundException	The specified path is invalid, (for example, it is on an unmapped drive).
UnauthorizedAccessException	path specified a directory. -or- The caller does not have the required permission.
FileNotFoundException	The file specified in path was not found.
NotSupportedException	path is in an invalid format.

Remarks

This method is equivalent to the FileStream(String, FileMode, FileAccess, FileShare) constructor overload with a FileMode value of Open, a FileAccess value of Read and a FileShare value of Read.

The path parameter is permitted to specify relative or absolute path information. Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, see GetCurrentDirectory.

For a list of common I/O tasks, see Common I/O Tasks.

Examples

The following example opens a file for reading.

Visual Basic

Imports System
Imports System.IO
Imports System.Text

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

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

        ' Open the stream and read it back.
        fs = File.OpenRead(path)
        Dim b(1024) 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

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

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

        // Delete the file if it exists.
        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 (FileStream fs = File.OpenRead(path)) 
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b,0,b.Length) > 0) 
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

Visual C++

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

int main()
{
   String^ path = "c:\\temp\\MyTest.txt";

   // Delete the file if it exists.
   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.
   FileStream^ fs = File::OpenRead( path );
   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;
   }
}

import System.*;
import System.IO.*;
import System.Text.*;

class Test
{
    public static void main(String[] args)
    {
        String path = "c:\\temp\\MyTest.txt";

        // Delete the file if it exists.
        if (!(File.Exists(path))) {
            // Create the file.
            FileStream fs = File.Create(path);
            try {
                ubyte info[] = (new UTF8Encoding(true)).GetBytes("This is " 
                    + "some text in the file.");

                // Add some information to the file.
                fs.Write(info, 0, info.length);
            }
            finally {
                fs.Dispose();
            }
        }

        // Open the stream and read it back.
        FileStream fs = File.OpenRead(path);
        try {
            ubyte b[] = new ubyte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);
            while (fs.Read(b, 0, b.length) > 0) {
                Console.WriteLine(temp.GetString(b));
            }
        }
        finally {
            fs.Dispose();
        }
    } //main
} //Test

Permissions

FileIOPermission
for reading from the specified file. Associated enumeration: FileIOPermissionAccess..::.Read

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information