FileStream Constructor (String, FileMode, FileAccess, FileShare)

FileStream Constructor (String, FileMode, FileAccess, FileShare)


Initializes a new instance of the FileStream class with the specified path, creation mode, read/write permission, and sharing permission.

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

public FileStream(
	string path,
	FileMode mode,
	FileAccess access,
	FileShare share


Type: System.String

A relative or absolute path for the file that the current FileStream object will encapsulate.

Type: System.IO.FileMode

A constant that determines how to open or create the file.

Type: System.IO.FileAccess

A constant that determines how the file can be accessed by the FileStream object. This also determines the values returned by the CanRead and CanWrite properties of the FileStream object. CanSeek is true if path specifies a disk file.

Type: System.IO.FileShare

A constant that determines how the file will be shared by processes.

Exception Condition

path is null.


path is an empty string (""), contains only white space, or contains one or more invalid characters.


path refers to a non-file device, such as "con:", "com1:", "lpt1:", etc. in an NTFS environment.


path refers to a non-file device, such as "con:", "com1:", "lpt1:", etc. in a non-NTFS environment.


The file cannot be found, such as when mode is FileMode.Truncate or FileMode.Open, and the file specified by path does not exist. The file must already exist in these modes.


An I/O error, such as specifying FileMode.CreateNew when the file specified by path already exists, occurred.


The system is running Windows 98 or Windows 98 Second Edition and share is set to FileShare.Delete.


The stream has been closed.


The caller does not have the required permission.


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


The access requested is not permitted by the operating system for the specified path, such as when access is Write or ReadWrite and the file or directory is set for read-only access.


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.


mode contains an invalid value.

The .NET Framework does not support direct access to physical disks through paths that are device names, such as "\\.\PHYSICALDRIVE0 ".

The path parameter can be a file name, including a file on a Universal Naming Convention (UNC) share.

The constructor is given read/write access to the file, and it is opened sharing Read access (that is, requests to open the file for writing by this or another process will fail until the FileStream object has been closed, but read attempts will succeed). The buffer size is set to the default size of 4096 bytes (4 KB).


path is not required to be a file stored on disk; it can be any part of a system that supports access through streams. For example, depending on the system, this class can access a physical device.

CanSeek is true for all FileStream objects that encapsulate files. If path indicates a device that does not support seeking, the CanSeek property on the resulting FileStream is false. For additional information, see CanSeek.


When you compile a set of characters with a particular cultural setting and retrieve those same characters with a different cultural setting, the characters might not be interpretable, and could cause an exception to be thrown.

For a list of common file and directory operations, see Common I/O Tasks.

This code example is part of a larger example provided for the Lock method.

using(FileStream fileStream = new FileStream(
    "Test#@@#.dat", FileMode.OpenOrCreate, 
    FileAccess.ReadWrite, FileShare.ReadWrite))

for reading, writing, and appending to files. Associated enumerations: FileIOPermissionAccess.Read, FileIOPermissionAccess.Write, and FileIOPermissionAccess.Append.

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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