enum System.IO.FileMode

Specifies that the operating system should create a new file. If the file already exists, it will be overwritten. This requires <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Write" /> permission. <see langword="FileMode.Create" /> is equivalent to requesting that if the file does not exist, use <see cref="F:System.IO.FileMode.CreateNew" /> ; otherwise, use <see cref="F:System.IO.FileMode.Truncate" /> . If the file already exists but is a hidden file, an <see cref="T:System.UnauthorizedAccessException" /> exception is thrown.

Specifies that the operating system should open an existing file. The ability to open the file is dependent on the value specified by the <see cref="T:System.IO.FileAccess" /> enumeration. A <see cref="T:System.IO.FileNotFoundException" /> exception is thrown if the file does not exist.

Specifies that the operating system should open a file if it exists; otherwise, a new file should be created. If the file is opened with <see langword="FileAccess.Read" /> , <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Read" /> permission is required. If the file access is <see langword="FileAccess.Write" /> , <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Write" /> permission is required. If the file is opened with <see langword="FileAccess.ReadWrite" /> , both <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Read" /> and <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Write" /> permissions are required.

Specifies 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 <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Write" /> permission. Attempts to read from a file opened with <see langword="FileMode.Truncate" /> cause an <see cref="T:System.ArgumentException" /> exception.

Opens the file if it exists and seeks to the end of the file, or creates a new file. This requires <see cref="F:System.Security.Permissions.FileIOPermissionAccess.Append" /> permission. <see langword="FileMode.Append" /> can be used only in conjunction with <see langword="FileAccess.Write" /> . Trying to seek to a position before the end of the file throws an <see cref="T:System.IO.IOException" /> exception, and any attempt to read fails and throws a <see cref="T:System.NotSupportedException" /> exception.