CreateFile3 function (fileapi.h)

Creates or opens a file or I/O device. The most commonly used I/O devices are as follows: file, file stream, directory, physical disk, volume, console buffer, tape drive, communications resource, mailslot, and pipe. The function returns a handle that can be used to access the file or device for various types of I/O depending on the file or device and the flags and attributes specified.

When called from a sandboxed packaged app, CreateFile3 is simplified. You can open only files or directories inside the ApplicationData.LocalFolder or Package.InstalledLocation directories. You can't open named pipes or mailslots or create encrypted files (FILE_ATTRIBUTE_ENCRYPTED).

Syntax

HANDLE CreateFile3(
  LPCWSTR                           lpFileName,
  DWORD                             dwDesiredAccess,
  DWORD                             dwShareMode,
  DWORD                             dwCreationDisposition,
  LPCREATEFILE3_EXTENDED_PARAMETERS pCreateExParams
);

Parameters

lpFileName

The name of the file or device to be created or opened.

For information on special device names, see Defining an MS-DOS Device Name.

To create a file stream, specify the name of the file, a colon, and then the name of the stream. For more information, see File Streams.

dwDesiredAccess

The requested access to the file or device, which can be summarized as read, write, both or neither zero.

The most commonly used values are GENERIC_READ, GENERIC_WRITE, or both (GENERIC_READ | GENERIC_WRITE). For more information, see Generic Access Rights, File Security and Access Rights, File Access Rights Constants, and ACCESS_MASK.

If this parameter is zero, the application can query certain metadata such as file, directory, or device attributes without accessing that file or device, even if GENERIC_READ access would have been denied.

You cannot request an access mode that conflicts with the sharing mode that is specified by the dwShareMode parameter in an open request that already has an open handle.

For more information, see the Remarks section of this topic and Creating and Opening Files.

dwShareMode

The requested sharing mode of the file or device, which can be read, write, both, delete, all of these, or none (refer to the following table). Access requests to attributes or extended attributes are not affected by this flag.

If this parameter is zero and CreateFile3 succeeds, the file or device cannot be shared and cannot be opened again until the handle to the file or device is closed. For more information, see the Remarks section.

You cannot request a sharing mode that conflicts with the access mode that is specified in an existing request that has an open handle. CreateFile3 would fail and the GetLastError function would return ERROR_SHARING_VIOLATION.

To enable a process to share a file or device while another process has the file or device open, use a compatible combination of one or more of the following values. For more information about valid combinations of this parameter with the dwDesiredAccess parameter, see Creating and Opening Files.

dwCreationDisposition

An action to take on a file or device that exists or does not exist.

For devices other than files, this parameter is usually set to OPEN_EXISTING.

For more information, see the Remarks section.

This parameter must be one of the following values, which cannot be combined:

pCreateExParams

Pointer to an optional CREATEFILE3_EXTENDED_PARAMETERS structure.

Return value

If the function succeeds, the return value is an open handle to the specified file, device, named pipe, or mail slot.

If the function fails, the return value is INVALID_HANDLE_VALUE. To get extended error information, call GetLastError. Possible errors include the following:

Remarks

CreateFile3 behaves exactly the same way as CreateFile2 with one exception; operations will fail if lpFileName is redirected via a reparse point or symbolic link. This behavior can be disabled with a new flag that can be added to the dwFileFlags.

To compile an application that uses the CreateFile3 function, define the _WIN32_WINNT macro as 0x0602 or later. For more information, see Using the Windows Headers.

CreateFile3 supports file interaction and most other types of I/O devices and mechanisms available to Windows developers. This section attempts to cover the varied issues developers may experience when using CreateFile3 in different contexts and with different I/O types. The text attempts to use the word file only when referring specifically to data stored in an actual file on a file system. However, some uses of file may be referring more generally to an I/O object that supports file-like mechanisms. This liberal use of the term file is particularly prevalent in constant names and parameter names because of the previously mentioned historical reasons.

When an application is finished using the object handle returned by CreateFile3, use the CloseHandle function to close the handle. This not only frees up system resources, but can have wider influence on things like sharing the file or device and committing data to disk. Specifics are noted within this topic as appropriate.

Some file systems, such as the NTFS file system, support compression or encryption for individual files and directories. On volumes that have a mounted file system with this support, a new file inherits the compression and encryption attributes of its directory.

You cannot use CreateFile3 to control compression, decompression, or decryption on a file or directory. For more information, see Creating and Opening Files, File Compression and Decompression, and File Encryption.

If the lpSecurityAttributes member of the CREATEFILE3_EXTENDED_PARAMETERS structure passed in the pCreateExParams parameter is NULL, the handle returned by CreateFile3 cannot be inherited by any child processes your application may create. The following information regarding this member also applies:

• If the bInheritHandle member variable is not FALSE, which is any nonzero value, then the handle can be inherited. Therefore it is critical this structure member be properly initialized to FALSE if you do not intend the handle to be inheritable.
• The access control lists (ACL) in the default security descriptor for a file or directory are inherited from its parent directory.
• The target file system must support security on files and directories for the lpSecurityDescriptor member to have an effect on them, which can be determined by using GetVolumeInformation.

In Windows 8 and Windows Server 2012, this function is supported by the following technologies:

Symbolic Link Behavior

If the call to this function creates a file, there is no change in behavior. Also, consider the following information regarding FILE_FLAG_OPEN_REPARSE_POINT flag for the dwFileFlags member of the CREATEFILE3_EXTENDED_PARAMETERS structure passed in the pCreateExParams parameter:

• If FILE_FLAG_OPEN_REPARSE_POINT is specified:
  • If an existing file is opened and it is a symbolic link, the handle returned is a handle to the symbolic link.
  • If TRUNCATE_EXISTING or FILE_FLAG_DELETE_ON_CLOSE are specified, the file affected is a symbolic link.
• If FILE_FLAG_OPEN_REPARSE_POINT is not specified:
  • If an existing file is opened and it is a symbolic link, the handle returned is a handle to the target.
  • If CREATE_ALWAYS, TRUNCATE_EXISTING, or FILE_FLAG_DELETE_ON_CLOSE are specified, the file affected is the target.

Files

If you rename or delete a file and then restore it shortly afterward, the system searches the cache for file information to restore. Cached information includes its short/long name pair and creation time.

If you call CreateFile3 on a file that is pending deletion as a result of a previous call to DeleteFile or DeleteFile2, the function fails. The operating system delays file deletion until all handles to the file are closed. GetLastError returns ERROR_ACCESS_DENIED.

The dwDesiredAccess parameter can be zero, allowing the application to query file attributes without accessing the file if the application is running with adequate security settings. This is useful to test for the existence of a file without opening it for read and/or write access, or to obtain other statistics about the file or directory. See Obtaining and Setting File Information and GetFileInformationByHandle.

When an application creates a file across a network, it is better to use GENERIC_READ | GENERIC_WRITE for dwDesiredAccess than to use GENERIC_WRITE alone. The resulting code is faster, because the redirector can use the cache manager and send fewer SMBs with more data. This combination also avoids an issue where writing to a file across a network can occasionally return ERROR_ACCESS_DENIED.

For more information, see Creating and Opening Files.

File Streams

On NTFS file systems, you can use CreateFile3 to create separate streams within a file. For more information, see File Streams.

Directories

An application cannot create a directory by using CreateFile3, therefore only the OPEN_EXISTING value is valid for dwCreationDisposition for this use case. To create a directory, the application must call CreateDirectory, CreateDirectoryEx, or CreateDirectory2.

To open a directory using CreateFile3, specify the FILE_FLAG_BACKUP_SEMANTICS flag as part of dwFileFlags member of the CREATEFILE3_EXTENDED_PARAMETERS structure passed in the pCreateExParams parameter. Appropriate security checks still apply when this flag is used without SE_BACKUP_NAME and SE_RESTORE_NAME privileges.

When using CreateFile3 to open a directory during defragmentation of a FAT or FAT32 file system volume, do not specify the MAXIMUM_ALLOWED access right. Access to the directory is denied if this is done. Specify the GENERIC_READ access right instead.

For more information, see About Directory Management.

Physical Disks and Volumes

Direct access to the disk or to a volume is restricted.

You can use the CreateFile3 function to open a physical disk drive or a volume, which returns a direct access storage device (DASD) handle that can be used with the DeviceIoControl function. This enables you to access the disk or volume directly, for example such disk metadata as the partition table. However, this type of access also exposes the disk drive or volume to potential data loss, because an incorrect write to a disk using this mechanism could make its contents inaccessible to the operating system. To ensure data integrity, be sure to become familiar with DeviceIoControl and how other APIs behave differently with a direct access handle as opposed to a file system handle.

The following requirements must be met for such a call to succeed:

• The caller must have administrative privileges. For more information, see Running with Special Privileges.
• The dwCreationDisposition parameter must have the OPEN_EXISTING flag.
• When opening a volume or floppy disk, the dwShareMode parameter must have the FILE_SHARE_WRITE flag.

When opening a physical drive x:, the lpFileName string should be the following form: "\.\PhysicalDriveX".

Hard disk numbers start at zero. The following table shows some examples of physical drive strings.

To obtain the physical drive identifier for a volume, open a handle to the volume and call the DeviceIoControl function with IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS. This control code returns the disk number and offset for each of the volume's one or more extents; a volume can span multiple physical disks.

For an example of opening a physical drive, see Calling DeviceIoControl.

When opening a volume or removable media drive (for example, a floppy disk drive or flash memory thumb drive), the lpFileName string should be the following form: "\\.\X:". Do not use a trailing backslash (\), which indicates the root directory of a drive.

The following table shows some examples of drive strings:

You can also open a volume by referring to its volume name. For more information, see Naming a Volume.

A volume contains one or more mounted file systems. Volume handles can be opened as noncached at the discretion of the particular file system, even when the noncached option is not specified in CreateFile3. You should assume that all Microsoft file systems open volume handles as noncached. The restrictions on noncached I/O for files also apply to volumes.

A file system may or may not require buffer alignment even though the data is noncached. However, if the noncached option is specified when opening a volume, buffer alignment is enforced regardless of the file system on the volume. It is recommended on all file systems that you open volume handles as noncached, and follow the noncached I/O restrictions.

Changer Device

The IOCTL_CHANGER_* control codes for DeviceIoControl accept a handle to a changer device. To open a changer device, use a file name of the following form: "\.\Changerx" where x is a number that indicates which device to open, starting with zero. To open changer device zero in an application that is written in C or C++, use the following file name: "\\.\Changer0".

Tape Drives

You can open tape drives by using a file name of the following form: "\.\TAPEx" where x is a number that indicates which drive to open, starting with tape drive zero. To open tape drive zero in an application that is written in C or C++, use the following file name: "\\.\TAPE0".

For more information, see Backup.

Communications Resources

The CreateFile3 function can create a handle to a communications resource, such as the serial port COM1. For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING, the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL. Read, write, or read/write access can be specified, and the handle can be opened for overlapped I/O.

To specify a COM port number greater than 9, use the following syntax: "\.\COM10". This syntax works for all port numbers and hardware that allows COM port numbers to be specified.

For more information about communications, see Communications.

Consoles

The CreateFile3 function can create a handle to console input (CONIN$). If the process has an open handle to it as a result of inheritance or duplication, it can also create a handle to the active screen buffer (CONOUT$). The calling process must be attached to an inherited console or one allocated by the AllocConsole function.

For console handles, set the CreateFile3 parameters as follows:

Set the members of the CREATEFILE3_EXTENDED_PARAMETERS structure passed in the pCreateExParams parameter as follows:

The following table shows various settings of dwDesiredAccess and lpFileName:

Mailslots

If CreateFile3 opens the client end of a mailslot, the function returns INVALID_HANDLE_VALUE if the mailslot client attempts to open a local mailslot before the mailslot server has created it with the CreateMailSlot function.

For more information, see Mailslots.

Pipes

If CreateFile3 opens the client end of a named pipe, the function uses any instance of the named pipe that is in the listening state. The opening process can duplicate the handle as many times as required, but after it is opened, the named pipe instance cannot be opened by another client. The access that is specified when a pipe is opened must be compatible with the access that is specified in the dwOpenMode parameter of the CreateNamedPipe function.

If the CreateNamedPipe function was not successfully called on the server prior to this operation, a pipe will not exist and CreateFile3 will fail with ERROR_FILE_NOT_FOUND.

If there is at least one active pipe instance but there are no available listener pipes on the server, which means all pipe instances are currently connected, CreateFile3 fails with ERROR_PIPE_BUSY.

For more information, see Pipes.

Requirements

See also

CreateDirectory2

DeleteFile2

RemoveDirectory2