CreateFile

Description

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.

To perform this operation as a transacted operation, which results in a handle that can be used for transacted I/O, use the CreateFileTransacted function.

Syntax

HANDLE WINAPI CreateFile(
  _In_      LPCTSTR lpFileName,
  _In_      DWORD dwDesiredAccess,
  _In_      DWORD dwShareMode,
  _In_opt_  LPSECURITY_ATTRIBUTES lpSecurityAttributes,
  _In_      DWORD dwCreationDisposition,
  _In_      DWORD dwFlagsAndAttributes,
  _In_opt_  HANDLE hTemplateFile
);

Parameters

lpFileName [in]

The name of the file or device to be created or opened. You may use either forward slashes (/) or backslashes (\) in this name.

In the ANSI version of this function, the name is limited to MAX_PATH characters. To extend this limit to 32,767 wide characters, call the Unicode version of the function and prepend "\\?\" to the path.

To create a file stream, specify the name of the file, a colon, and then the name of the stream.

dwDesiredAccess [in]

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).

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.

dwShareMode [in]

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 CreateFile succeeds, the file or device cannot be shared and cannot be opened again until the handle to the file or device is closed.

You cannot request a sharing mode that conflicts with the access mode that is specified in an existing request that has an open handle. CreateFile 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.

Note The sharing options for each open handle remain in effect until that handle is closed, regardless of process context.

Value	Meaning
0 0x00000000	Prevents other processes from opening a file or device if they request delete, read, or write access.
FILE_SHARE_DELETE 0x00000004	Enables subsequent open operations on a file or device to request delete access. Otherwise, other processes cannot open the file or device if they request delete access. If this flag is not specified, but the file or device has been opened for delete access, the function fails. Note Delete access allows both delete and rename operations.
FILE_SHARE_READ 0x00000001	Enables subsequent open operations on a file or device to request read access. Otherwise, other processes cannot open the file or device if they request read access. If this flag is not specified, but the file or device has been opened for read access, the function fails.
FILE_SHARE_WRITE 0x00000002	Enables subsequent open operations on a file or device to request write access. Otherwise, other processes cannot open the file or device if they request write access. If this flag is not specified, but the file or device has been opened for write access or has a file mapping with write access, the function fails.

lpSecurityAttributes [in, optional]

A pointer to a SECURITY_ATTRIBUTES structure that contains two separate but related data members: an optional security descriptor, and a Boolean value that determines whether the returned handle can be inherited by child processes.

This parameter can be NULL.

If this parameter is NULL, the handle returned by CreateFile cannot be inherited by any child processes the application may create and the file or device associated with the returned handle gets a default security descriptor.

The lpSecurityDescriptor member of the structure specifies a SECURITY_DESCRIPTOR for a file or device. If this member is NULL, the file or device associated with the returned handle is assigned a default security descriptor.

CreateFile ignores the lpSecurityDescriptor member when opening an existing file or device, but continues to use the bInheritHandle member.

The bInheritHandlemember of the structure specifies whether the returned handle can be inherited.

dwCreationDisposition [in]

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.

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

Value	Meaning
CREATE_ALWAYS 2	Creates a new file, always. If the specified file exists and is writable, the function overwrites the file, the function succeeds, and last-error code is set to ERROR_ALREADY_EXISTS (183). If the specified file does not exist and is a valid path, a new file is created, the function succeeds, and the last-error code is set to zero.
CREATE_NEW 1	Creates a new file, only if it does not already exist. If the specified file exists, the function fails and the last-error code is set to ERROR_FILE_EXISTS (80). If the specified file does not exist and is a valid path to a writable location, a new file is created.
OPEN_ALWAYS 4	Opens a file, always. If the specified file exists, the function succeeds and the last-error code is set to ERROR_ALREADY_EXISTS (183). If the specified file does not exist and is a valid path to a writable location, the function creates a file and the last-error code is set to zero.
OPEN_EXISTING 3	Opens a file or device, only if it exists. If the specified file or device does not exist, the function fails and the last-error code is set to ERROR_FILE_NOT_FOUND (2).
TRUNCATE_EXISTING 5	Opens a file and truncates it so that its size is zero bytes, only if it exists. If the specified file does not exist, the function fails and the last-error code is set to ERROR_FILE_NOT_FOUND (2). The calling process must open the file with the GENERIC_WRITE bit set as part of the dwDesiredAccess parameter.

dwFlagsAndAttributes [in]

The file or device attributes and flags, FILE_ATTRIBUTE_NORMAL being the most common default value for files.

This parameter can include any combination of the available file attributes (FILE_ATTRIBUTE_*). All other file attributes override FILE_ATTRIBUTE_NORMAL.

This parameter can also contain combinations of flags (FILE_FLAG_*) for control of file or device caching behavior, access modes, and other special-purpose flags. These combine with any FILE_ATTRIBUTE_* values.

This parameter can also contain Security Quality of Service (SQOS) information by specifying the SECURITY_SQOS_PRESENT flag. Additional SQOS-related flags information is presented in the table following the attributes and flags tables.

Note When CreateFile opens an existing file, it generally combines the file flags with the file attributes of the existing file, and ignores any file attributes supplied as part of dwFlagsAndAttributes. Special cases are detailed in Creating and Opening Files.

Some of the following file attributes and flags may only apply to files and not necessarily all other types of devices that CreateFile can open.

For more advanced access to file attributes, see SetFileAttributes.

Attribute	Meaning
FILE_ATTRIBUTE_ARCHIVE 32 (0x20)	The file should be archived. Applications use this attribute to mark files for backup or removal.
FILE_ATTRIBUTE_ENCRYPTED 16384 (0x4000)	The file or directory is encrypted. For a file, this means that all data in the file is encrypted. For a directory, this means that encryption is the default for newly created files and subdirectories. This flag has no effect if FILE_ATTRIBUTE_SYSTEM is also specified. This flag is not supported on Home, Home Premium, Starter, or ARM editions of Windows.
FILE_ATTRIBUTE_HIDDEN 2 (0x2)	The file is hidden. Do not include it in an ordinary directory listing.
FILE_ATTRIBUTE_NORMAL 128 (0x80)	The file does not have other attributes set. This attribute is valid only if used alone.
FILE_ATTRIBUTE_OFFLINE 4096 (0x1000)	The data of a file is not immediately available. This attribute indicates that file data is physically moved to offline storage. This attribute is used by Remote Storage, the hierarchical storage management software. Applications should not arbitrarily change this attribute.
FILE_ATTRIBUTE_READONLY 1 (0x1)	The file is read only. Applications can read the file, but cannot write to or delete it.
FILE_ATTRIBUTE_SYSTEM 4 (0x4)	The file is part of or used exclusively by an operating system.
FILE_ATTRIBUTE_TEMPORARY 256 (0x100)	The file is being used for temporary storage. For more information, see the Caching Behavior section of this topic.

Flag	Meaning
FILE_FLAG_BACKUP_SEMANTICS 0x02000000	The file is being opened or created for a backup or restore operation. The system ensures that the calling process overrides file security checks when the process has SE_BACKUP_NAME and SE_RESTORE_NAME privileges. You must set this flag to obtain a handle to a directory. A directory handle can be passed to some functions instead of a file handle.
FILE_FLAG_DELETE_ON_CLOSE 0x04000000	The file is to be deleted immediately after all of its handles are closed, which includes the specified handle and any other open or duplicated handles. If there are existing open handles to a file, the call fails unless they were all opened with the FILE_SHARE_DELETE share mode. Subsequent open requests for the file fail, unless the FILE_SHARE_DELETE share mode is specified.
FILE_FLAG_NO_BUFFERING 0x20000000	The file or device is being opened with no system caching for data reads and writes. This flag does not affect hard disk caching or memory mapped files. There are strict requirements for successfully working with files opened with CreateFile using the FILE_FLAG_NO_BUFFERING flag, for details see File Buffering.
FILE_FLAG_OPEN_NO_RECALL 0x00100000	The file data is requested, but it should continue to be located in remote storage. It should not be transported back to local storage. This flag is for use by remote storage systems.
FILE_FLAG_OPEN_REPARSE_POINT 0x00200000	Normal reparse point processing will not occur; CreateFile will attempt to open the reparse point. When a file is opened, a file handle is returned, whether or not the filter that controls the reparse point is operational. This flag cannot be used with the CREATE_ALWAYS flag. If the file is not a reparse point, then this flag is ignored.
FILE_FLAG_OVERLAPPED 0x40000000	The file or device is being opened or created for asynchronous I/O. When subsequent I/O operations are completed on this handle, the event specified in the OVERLAPPED structure will be set to the signaled state. If this flag is specified, the file can be used for simultaneous read and write operations. If this flag is not specified, then I/O operations are serialized, even if the calls to the read and write functions specify an OVERLAPPED structure.
FILE_FLAG_POSIX_SEMANTICS 0x0100000	Access will occur according to POSIX rules. This includes allowing multiple files with names, differing only in case, for file systems that support that naming. Use care when using this option, because files created with this flag may not be accessible by applications that are written for MS-DOS or 16-bit Windows.
FILE_FLAG_RANDOM_ACCESS 0x10000000	Access is intended to be random. The system can use this as a hint to optimize file caching. This flag has no effect if the file system does not support cached I/O and FILE_FLAG_NO_BUFFERING.
FILE_FLAG_SESSION_AWARE 0x00800000	The file or device is being opened with session awareness. If this flag is not specified, then per-session devices (such as a redirected USB device) cannot be opened by processes running in session 0. This flag has no effect for callers not in session 0. This flag is supported only on server editions of Windows. Windows Server 2008 R2, Windows Server 2008, and Windows Server 2003: This flag is not supported before Windows Server 2012.
FILE_FLAG_SEQUENTIAL_SCAN 0x08000000	Access is intended to be sequential from beginning to end. The system can use this as a hint to optimize file caching. This flag should not be used if read-behind (that is, reverse scans) will be used. This flag has no effect if the file system does not support cached I/O and FILE_FLAG_NO_BUFFERING.
FILE_FLAG_WRITE_THROUGH 0x80000000	Write operations will not go through any intermediate cache, they will go directly to disk.

The dwFlagsAndAttributesparameter can also specify SQOS information. When the calling application specifies the SECURITY_SQOS_PRESENT flag as part of dwFlagsAndAttributes, it can also contain one or more of the following values.

Security flag	Meaning
SECURITY_ANONYMOUS	Impersonates a client at the Anonymous impersonation level.
SECURITY_CONTEXT_TRACKING	The security tracking mode is dynamic. If this flag is not specified, the security tracking mode is static.
SECURITY_DELEGATION	Impersonates a client at the Delegation impersonation level.
SECURITY_EFFECTIVE_ONLY	Only the enabled aspects of the client's security context are available to the server. If you do not specify this flag, all aspects of the client's security context are available. This allows the client to limit the groups and privileges that a server can use while impersonating the client.
SECURITY_IDENTIFICATION	Impersonates a client at the Identification impersonation level.
SECURITY_IMPERSONATION	Impersonate a client at the impersonation level. This is the default behavior if no other flags are specified along with the SECURITY_SQOS_PRESENT flag.

hTemplateFile [in, optional]

A valid handle to a template file with the GENERIC_READ access right. The template file supplies file attributes and extended attributes for the file that is being created.

This parameter can be NULL.

When opening an existing file, CreateFile ignores this parameter.

When opening a new encrypted file, the file inherits the discretionary access control list from its parent directory.

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.