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File.Open Method (String, FileMode, FileAccess)

Opens a FileStream on the specified path, with the specified mode and access.

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

Public Shared Function Open ( _
	path As String, _
	mode As FileMode, _
	access As FileAccess _
) As FileStream
Dim path As String 
Dim mode As FileMode 
Dim access As FileAccess 
Dim returnValue As FileStream 

returnValue = File.Open(path, mode, _


Type: System.String

The file to open.

Type: System.IO.FileMode

A FileMode value that specifies whether a file is created if one does not exist, and determines whether the contents of existing files are retained or overwritten.

Type: System.IO.FileAccess

A FileAccess value that specifies the operations that can be performed on the file.

Return Value

Type: System.IO.FileStream
An unshared FileStream that provides access to the specified file, with the specified mode and access.


path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by InvalidPathChars.


access specified Read and mode specified Create, CreateNew, Truncate, or Append.


path is Nothing.


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.


The specified path is invalid, (for example, it is on an unmapped drive).


An I/O error occurred while opening the file.


path specified a file that is read-only and access is not Read.


path specified a directory.


The caller does not have the required permission.


mode is Create and the specified file is a hidden file.


mode or access specified an invalid value.


The file specified in path was not found.


path is in an invalid format.

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.

The following example opens a file with read-only access.

Imports System
Imports System.IO
Imports System.Text

Public Class Test
    Public Shared Sub Main()
        ' This sample assumes that you have a folder named "c:\temp" on your computer. 
        Dim filePath As String = "c:\temp\MyTest.txt" 
        Dim fs As FileStream

        ' Delete the file if it exists. 
        If File.Exists(filePath) = True Then
        End If 

        ' Create the file.
        fs = File.Create(filePath)
        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)

        ' Open the stream and read it back.
        fs = File.Open(filePath, FileMode.Open, FileAccess.Read)
        Dim b(1024) As Byte
        Dim temp As UTF8Encoding = New UTF8Encoding(True)

        ' Display the information on the console.
        Do While fs.Read(b, 0, b.Length) > 0

            ' Try to write to the file
            fs.Write(b, 0, b.Length)

        Catch e As Exception
            Console.WriteLine("Writing was disallowed, as expected: " & e.ToString())

        End Try


    End Sub 
End Class

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, 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, Zune

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.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0