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FileInfo.Open Method (FileMode, FileAccess, FileShare)

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

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

public FileStream Open(
	FileMode mode,
	FileAccess access,
	FileShare share


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.
Type: System.IO.FileShare
A FileShare constant specifying the type of access other FileStream objects have to this file.

Return Value

Type: System.IO.FileStream
A FileStream object opened with the specified mode, access, and sharing options.


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.

The following example demonstrates opening a file for reading and writing, but disallowing access to other users or processes.

using System;
using System.IO;

public class OpenTest 
    public static void Main() 
        // Open an existing file, or create a new one.
        FileInfo fi = new FileInfo("temp.txt");

        // Open the file just specified such that no one else can use it.
        FileStream fs = fi.Open( FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None );

        // Create another reference to the same file.
        FileInfo nextfi = new FileInfo("temp.txt");        

            // Try opening the same file, which was locked by the previous process.
            nextfi.Open( FileMode.OpenOrCreate, FileAccess.Read );

            Console.WriteLine("The file was not locked, and was opened by a second process.");
        catch (IOException) 
            Console.WriteLine("The file could not be opened because it was locked by another process.");
        catch (Exception e) 

        // Close the file so it can be deleted.

//This code produces output similar to the following; 
//results may vary based on the computer/file structure/etc.:
//The file could not be opened because it was locked by another process.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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