QFileDevice

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

Inheritance diagram of PySide2.QtCore.QFileDevice

Inherited by: QFile, QSaveFile, QTemporaryFile

New in version 5.0.

Synopsis

Functions

Virtual functions

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 QTemporaryFile , by providing all the operations that can be done on files that have been opened by QFile or QTemporaryFile .

class QFileDevice

QFileDevice(parent)

Parameters

parentQObject

PySide2.QtCore.QFileDevice.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.

PySide2.QtCore.QFileDevice.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()

New in version 5.10.

PySide2.QtCore.QFileDevice.Permission

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 anyone.

QFileDevice.WriteOther

The file is writable by anyone.

QFileDevice.ExeOther

The file is executable by anyone.

Warning

Because of differences in the platforms supported by Qt, the semantics of , and 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:

extern Q_CORE_EXPORT int qt_ntfs_permission_lookup;

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

qt_ntfs_permission_lookup += 1 // turn checking on
qt_ntfs_permission_lookup += 1 // turn it off again
PySide2.QtCore.QFileDevice.FileHandleFlag

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.

PySide2.QtCore.QFileDevice.MemoryMapFlags

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.

PySide2.QtCore.QFileDevice.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()

PySide2.QtCore.QFileDevice.fileName()
Return type

unicode

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

PySide2.QtCore.QFileDevice.fileTime(time)
Parameters

timeFileTime

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()

PySide2.QtCore.QFileDevice.flush()
Return type

bool

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

PySide2.QtCore.QFileDevice.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, returns -1.

See also

QSocketNotifier

PySide2.QtCore.QFileDevice.map(offset, size[, flags=NoOptions])
Parameters
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()

PySide2.QtCore.QFileDevice.permissions()
Return type

Permissions

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

See also

setPermissions()

PySide2.QtCore.QFileDevice.resize(sz)
Parameters

szqint64

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.

See also

size()

PySide2.QtCore.QFileDevice.setFileTime(newDate, fileTime)
Parameters
Return type

bool

Sets the file time specified by fileTime to newDate , returning true if successful; otherwise returns false.

Note

The file must be open to use this function.

See also

fileTime() FileTime

PySide2.QtCore.QFileDevice.setPermissions(permissionSpec)
Parameters

permissionSpecPermissions

Return type

bool

Sets the permissions for the file to the permissions specified. Returns true if successful, or false if the permissions cannot be modified.

Warning

This function does not manipulate ACLs, which may limit its effectiveness.

See also

permissions()

PySide2.QtCore.QFileDevice.unmap(address)
Parameters

addressuchar

Return type

bool

Unmaps the memory address .

Returns true if the unmap succeeds; false otherwise.

See also

map()

PySide2.QtCore.QFileDevice.unsetError()

Sets the file’s error to NoError .

See also

error()