Open Method (FileMode, FileAccess)

FileInfo.Open Method (FileMode, FileAccess)

Opens a file in the specified mode with read, write, or read/write access.

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

public FileStream Open(
	FileMode mode,
	FileAccess access


Type: System.IO.FileMode

A FileMode constant specifying the mode (for example, Open or Append) in which to open the file.

Type: System.IO.FileAccess

A FileAccess constant specifying whether to open the file with Read, Write, or ReadWrite file access.

Return Value

Type: System.IO.FileStream
A FileStream object opened in the specified mode and access, and unshared.


The caller does not have the required permission.


path is empty or contains only white spaces.


The file is not found.


One or more arguments is null.


path is read-only or is a directory.


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


The file is already open.

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

The following example opens a file as read-only and reads from 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.Open(FileMode.Open, FileAccess.Read)) 
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);
            while (fs.Read(b,0,b.Length) > 0) 

                //Try to write to the file.
            catch (Exception e) 
                Console.WriteLine("Writing was disallowed, as expected: {0}",
//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. 
//Writing was disallowed, as expected: System.NotSupportedException: Stream does  
//not support writing. 
//   at System.IO.__Error.WriteNotSupported() 
//   at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count) 
//   at Test.Main() in C:\Documents and Settings\My Computer\My Documents\ 
//Visual Studio 2005\Projects\finfo open2\finfo open2\Program.cs:line 39

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

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