FileMode Enumeration

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

Specifies how the operating system should open a file.

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

[SerializableAttribute]
public enum FileMode

Member nameDescription
CreateNewSpecifies that the operating system should create a new file. This requires FileIOPermissionAccess.Write permission. If the file already exists, an IOException exception is thrown.
CreateSpecifies that the operating system should create a new file. If the file already exists, it will be overwritten. This requires FileIOPermissionAccess.Write permission. FileMode.Create is equivalent to requesting that if the file does not exist, use CreateNew; otherwise, use Truncate. If the file already exists but is a hidden file, an UnauthorizedAccessException exception is thrown.
OpenSpecifies that the operating system should open an existing file. The ability to open the file is dependent on the value specified by the FileAccess enumeration. A FileNotFoundException exception is thrown if the file does not exist.
OpenOrCreateSpecifies that the operating system should open a file if it exists; otherwise, a new file should be created. If the file is opened with FileAccess.Read, FileIOPermissionAccess.Read permission is required. If the file access is FileAccess.Write, FileIOPermissionAccess.Write permission is required. If the file is opened with FileAccess.ReadWrite, both FileIOPermissionAccess.Read and FileIOPermissionAccess.Write permissions are required.
TruncateSpecifies that the operating system should open an existing file. When the file is opened, it should be truncated so that its size is zero bytes. This requires FileIOPermissionAccess.Write permission. Attempts to read from a file opened with FileMode.Truncate cause an ArgumentException exception.
AppendOpens the file if it exists and seeks to the end of the file, or creates a new file. This requires FileIOPermissionAccess.Append permission. FileMode.Append can be used only in conjunction with FileAccess.Write. Trying to seek to a position before the end of the file throws an IOException exception, and any attempt to read fails and throws a NotSupportedException exception.

FileMode parameters control whether a file is overwritten, created, opened, or some combination thereof. Use Open to open an existing file. To append to a file, use Append. To truncate a file or create a file if it doesn't exist, use Create.

Show: