class QFileDevice#

The QFileDevice class provides an interface for reading from and writing to open files. More…

Inherited by: QSaveFile, QFile, QTemporaryFile

Synopsis#

Methods#

def __init__()
def error()
def fileTime()
def flush()
def handle()
def map()
def setFileTime()
def unmap()
def unsetError()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

QFileDevice is the base class for I/O devices that can read and write text and binary files and resources . QFile offers the main functionality, QFileDevice serves as a base class for sharing functionality with other file devices such as QSaveFile , by providing all the operations that can be done on files that have been opened by QFile or QSaveFile .

See also

QFile QSaveFile

class FileError#

This enum describes the errors that may be returned by the error() function.

Constant

Description

QFileDevice.NoError

No error occurred.

QFileDevice.ReadError

An error occurred when reading from the file.

QFileDevice.WriteError

An error occurred when writing to the file.

QFileDevice.FatalError

A fatal error occurred.

QFileDevice.ResourceError

Out of resources (e.g., too many open files, out of memory, etc.)

QFileDevice.OpenError

The file could not be opened.

QFileDevice.AbortError

The operation was aborted.

QFileDevice.TimeOutError

A timeout occurred.

QFileDevice.UnspecifiedError

An unspecified error occurred.

QFileDevice.RemoveError

The file could not be removed.

QFileDevice.RenameError

The file could not be renamed.

QFileDevice.PositionError

The position in the file could not be changed.

QFileDevice.ResizeError

The file could not be resized.

QFileDevice.PermissionsError

The file could not be accessed.

QFileDevice.CopyError

The file could not be copied.

Constant	Description
QFileDevice.NoError	No error occurred.
QFileDevice.ReadError	An error occurred when reading from the file.
QFileDevice.WriteError	An error occurred when writing to the file.
QFileDevice.FatalError	A fatal error occurred.
QFileDevice.ResourceError	Out of resources (e.g., too many open files, out of memory, etc.)
QFileDevice.OpenError	The file could not be opened.
QFileDevice.AbortError	The operation was aborted.
QFileDevice.TimeOutError	A timeout occurred.
QFileDevice.UnspecifiedError	An unspecified error occurred.
QFileDevice.RemoveError	The file could not be removed.
QFileDevice.RenameError	The file could not be renamed.
QFileDevice.PositionError	The position in the file could not be changed.
QFileDevice.ResizeError	The file could not be resized.
QFileDevice.PermissionsError	The file could not be accessed.
QFileDevice.CopyError	The file could not be copied.

class FileTime#

This enum is used by the fileTime() and setFileTime() functions.

Constant

Description

QFileDevice.FileAccessTime

When the file was most recently accessed (e.g. read or written to).

QFileDevice.FileBirthTime

When the file was created (may not be not supported on UNIX).

QFileDevice.FileMetadataChangeTime

When the file’s metadata was last changed.

QFileDevice.FileModificationTime

When the file was most recently modified.

See also

setFileTime() fileTime() fileTime()

Constant	Description
QFileDevice.FileAccessTime	When the file was most recently accessed (e.g. read or written to).
QFileDevice.FileBirthTime	When the file was created (may not be not supported on UNIX).
QFileDevice.FileMetadataChangeTime	When the file’s metadata was last changed.
QFileDevice.FileModificationTime	When the file was most recently modified.

class Permission#

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

(inherits enum.Flag) This enum is used by the permission() function to report the permissions and ownership of a file. The values may be OR-ed together to test multiple permissions and ownership values.

Constant

Description

QFileDevice.ReadOwner

The file is readable by the owner of the file.

QFileDevice.WriteOwner

The file is writable by the owner of the file.

QFileDevice.ExeOwner

The file is executable by the owner of the file.

QFileDevice.ReadUser

The file is readable by the user.

QFileDevice.WriteUser

The file is writable by the user.

QFileDevice.ExeUser

The file is executable by the user.

QFileDevice.ReadGroup

The file is readable by the group.

QFileDevice.WriteGroup

The file is writable by the group.

QFileDevice.ExeGroup

The file is executable by the group.

QFileDevice.ReadOther

The file is readable by others.

QFileDevice.WriteOther

The file is writable by others.

QFileDevice.ExeOther

The file is executable by others.

Constant	Description
QFileDevice.ReadOwner	The file is readable by the owner of the file.
QFileDevice.WriteOwner	The file is writable by the owner of the file.
QFileDevice.ExeOwner	The file is executable by the owner of the file.
QFileDevice.ReadUser	The file is readable by the user.
QFileDevice.WriteUser	The file is writable by the user.
QFileDevice.ExeUser	The file is executable by the user.
QFileDevice.ReadGroup	The file is readable by the group.
QFileDevice.WriteGroup	The file is writable by the group.
QFileDevice.ExeGroup	The file is executable by the group.
QFileDevice.ReadOther	The file is readable by others.
QFileDevice.WriteOther	The file is writable by others.
QFileDevice.ExeOther	The file is executable by others.

Warning

Because of differences in the platforms supported by Qt, the semantics of ReadUser, WriteUser and ExeUser are platform-dependent: On Unix, the rights of the owner of the file are returned and on Windows the rights of the current user are returned. This behavior might change in a future Qt version.

Note

On NTFS file systems, ownership and permissions checking is disabled by default for performance reasons. To enable it, include the following line:

Q_CORE_EXPORT = extern()

Permission checking is then turned on and off by incrementing and decrementing qt_ntfs_permission_lookup by 1.

qt_ntfs_permission_lookup++ # turn checking on
qt_ntfs_permission_lookup-- # turn it off again

Note

Since this is a non-atomic global variable, it is only safe to increment or decrement qt_ntfs_permission_lookup before any threads other than the main thread have started or after every thread other than the main thread has ended.

Note

From Qt 6.6 the variable qt_ntfs_permission_lookup is deprecated. Please use the following alternatives.

The safe and easy way to manage permission checks is to use the RAII class QNtfsPermissionCheckGuard.

def complexFunction():

    QNtfsPermissionCheckGuard permissionGuard # check is enabled
    # do complex things here that need permission check enabled
} // as the guard goes out of scope the check is disabled

If you need more fine-grained control, it is possible to manage the permission with the following functions instead:

qAreNtfsPermissionChecksEnabled() # check status
qEnableNtfsPermissionChecks() # turn checking on
qDisableNtfsPermissionChecks() # turn it off again

class FileHandleFlag#

(inherits enum.Flag) This enum is used when opening a file to specify additional options which only apply to files and not to a generic QIODevice .

Constant

Description

QFileDevice.AutoCloseHandle

The file handle passed into open() should be closed by close() , the default behavior is that close just flushes the file and the application is responsible for closing the file handle. When opening a file by name, this flag is ignored as Qt always owns the file handle and must close it.

QFileDevice.DontCloseHandle

If not explicitly closed, the underlying file handle is left open when the QFile object is destroyed.

Constant	Description
QFileDevice.AutoCloseHandle	The file handle passed into `open()` should be closed by `close()` , the default behavior is that close just flushes the file and the application is responsible for closing the file handle. When opening a file by name, this flag is ignored as Qt always owns the file handle and must close it.
QFileDevice.DontCloseHandle	If not explicitly closed, the underlying file handle is left open when the `QFile` object is destroyed.

class MemoryMapFlag#

(inherits enum.Flag) This enum describes special options that may be used by the map() function.

Constant

Description

QFileDevice.NoOptions

No options.

QFileDevice.MapPrivateOption

The mapped memory will be private, so any modifications will not be visible to other processes and will not be written to disk. Any such modifications will be lost when the memory is unmapped. It is unspecified whether modifications made to the file made after the mapping is created will be visible through the mapped memory. This enum value was introduced in Qt 5.4.

Constant	Description
QFileDevice.NoOptions	No options.
QFileDevice.MapPrivateOption	The mapped memory will be private, so any modifications will not be visible to other processes and will not be written to disk. Any such modifications will be lost when the memory is unmapped. It is unspecified whether modifications made to the file made after the mapping is created will be visible through the mapped memory. This enum value was introduced in Qt 5.4.

__init__()#

__init__(parent)

Parameters:: parent – QObject

error()#

Return type:: FileError

Returns the file error status.

The I/O device status returns an error code. For example, if open() returns false, or a read/write operation returns -1, this function can be called to find out the reason why the operation failed.

See also

unsetError()

fileName()#

Return type:: str

Returns the name of the file. The default implementation in QFileDevice returns a null string.

fileTime(time)#

Parameters:: time – FileTime
Return type:: QDateTime

Returns the file time specified by time. If the time cannot be determined return QDateTime() (an invalid date time).

See also

setFileTime() FileTime isValid()

flush()#

Return type:: bool

Flushes any buffered data to the file. Returns true if successful; otherwise returns false.

handle()#

Return type:: int

Returns the file handle of the file.

This is a small positive integer, suitable for use with C library functions such as fdopen() and fcntl(). On systems that use file descriptors for sockets (i.e. Unix systems, but not Windows) the handle can be used with QSocketNotifier as well.

If the file is not open, or there is an error, handle() returns -1.

See also

QSocketNotifier

map(offset, size[, flags=QFileDevice.MemoryMapFlag.NoOptions])#

Parameters:

offset – int
size – int
flags – Combination of MemoryMapFlag

Return type:

PyObject

Maps size bytes of the file into memory starting at offset. A file should be open for a map to succeed but the file does not need to stay open after the memory has been mapped. When the QFile is destroyed or a new file is opened with this object, any maps that have not been unmapped will automatically be unmapped.

The mapping will have the same open mode as the file (read and/or write), except when using MapPrivateOption , in which case it is always possible to write to the mapped memory.

Any mapping options can be passed through flags.

Returns a pointer to the memory or None if there is an error.

See also

unmap()

permissions()#

Return type:: Combination of Permission

Returns the complete OR-ed together combination of QFile::Permission for the file.

See also

setPermissions()

resize(sz)#

Parameters:: sz – int
Return type:: bool

Sets the file size (in bytes) sz. Returns true if the resize succeeds; false otherwise. If sz is larger than the file currently is, the new bytes will be set to 0; if sz is smaller, the file is simply truncated.

Warning

This function can fail if the file doesn’t exist.