The QSaveFile class provides an interface for safely writing to files. More...

Inheritance diagram for QSaveFile:

Public Methods
	QSaveFile (const QString &name)

	QSaveFile (const QString &name, QObject *parent)

	QSaveFile (QObject *parent=nullptr)

	~QSaveFile ()

void	cancelWriting ()

bool	commit ()

bool	directWriteFallback () const

QString	fileName () const override

bool	open (OpenMode mode) override

void	setDirectWriteFallback (bool enabled)

void	setFileName (const QString &name)

Public Methods inherited from QFileDevice
	~QFileDevice ()

bool	atEnd () const override

FileError	error () const

bool	flush ()

int	handle () const

bool	isSequential () const override

uchar *	map (qint64 offset, qint64 size, MemoryMapFlags flags=NoOptions)

virtual Permissions	permissions () const

qint64	pos () const override

virtual bool	resize (qint64 size)

bool	seek (qint64 pos) override

virtual bool	setPermissions (Permissions permissionSpec)

qint64	size () const override

bool	unmap (uchar *address)

void	unsetError ()

Public Methods inherited from QIODevice
	QIODevice ()

	QIODevice (QObject *parent)

virtual	~QIODevice ()

virtual qint64	bytesAvailable () const

virtual qint64	bytesToWrite () const

virtual bool	canReadLine () const

QString	errorString () const

bool	getChar (char *c)

bool	isOpen () const

bool	isReadable () const

bool	isTextModeEnabled () const

bool	isWritable () const

OpenMode	openMode () const

qint64	peek (char *data, qint64 maxSize)

QByteArray	peek (qint64 maxSize)

bool	putChar (char c)

qint64	read (char *data, qint64 maxSize)

QByteArray	read (qint64 maxSize)

QByteArray	readAll ()

qint64	readLine (char *data, qint64 maxSize)

QByteArray	readLine (qint64 maxSize=0)

virtual bool	reset ()

void	setTextModeEnabled (bool enabled)

void	ungetChar (char c)

virtual bool	waitForBytesWritten (int msecs)

virtual bool	waitForReadyRead (int msecs)

qint64	write (const char *data)

qint64	write (const char *data, qint64 maxSize)

qint64	write (const QByteArray &data)

Public Methods inherited from QObject
	QObject (QObject *parent=nullptr)

	~QObject ()

bool	blockSignals (bool block)

const QList< QObject * > &	children () const

bool	connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

bool	disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

bool	disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const

void	dumpObjectInfo ()

void	dumpObjectTree ()

QList< QString >	dynamicPropertyNames () const

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

template<typename T >
T	findChild (const QString &childName=QString ()) const

template<class T >
QList< T >	findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<class T >
QList< T >	findChildren (const QString &childName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

bool	inherits (const QString &className) const

void	installEventFilter (QObject *filterObj)

bool	isWidgetType () const

bool	isWindowType () const

void	killTimer (int id)

const QMetaObject *	metaObject () const

void	moveToThread (QThread *targetThread)

QString	objectName () const

QObject *	parent () const

template<class T = QVariant>
T	property (const QString &name) const

void	removeEventFilter (QObject *obj)

void	setObjectName (const QString &name)

void	setParent (QObject *parent)

bool	setProperty (const QString &name, const QVariant &value)

bool	signalsBlocked () const

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

QThread *	thread () const

Protected Methods
qint64	writeData (const char *data, qint64 len) override

Protected Methods inherited from QFileDevice
qint64	readData (char *data, qint64 maxSize) override

qint64	readLineData (char *data, qint64 maxSize) override

Protected Methods inherited from QIODevice
void	setErrorString (const QString &errorString)

void	setOpenMode (OpenMode openMode)

Protected Methods inherited from QObject
virtual void	childEvent (QChildEvent *event)

virtual void	connectNotify (const QMetaMethod &signalMethod) const

virtual void	customEvent (QEvent *event)

virtual void	disconnectNotify (const QMetaMethod &signalMethod) const

bool	isSignalConnected (const QMetaMethod &signalMethod) const

int	receivers (const QString &signal) const

QObject *	sender () const

int	senderSignalIndex () const

virtual void	timerEvent (QTimerEvent *event)

Additional Inherited Members
Public Typedefs inherited from QFileDevice
using	FileHandleFlags = QFlags< FileHandleFlag >

using	Permissions = QFlags< Permission >

Public Typedefs inherited from QIODevice
using	OpenMode = QFlags< OpenModeFlag >

Public Types inherited from QFileDevice
enum	FileError

enum	FileHandleFlag

enum	MemoryMapFlags

enum	Permission

Public Types inherited from QIODevice
enum	OpenModeFlag

Public Signals inherited from QIODevice
void	aboutToClose ()

void	bytesWritten (qint64 bytes)

void	readChannelFinished ()

void	readyRead ()

Public Signals inherited from QObject
void	destroyed (QObject *obj=nullptr)

void	objectNameChanged (const QString &objectName)

Public Slots inherited from QObject
void	deleteLater ()

Static Public Methods inherited from QObject
static bool	connect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

static bool	connect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())

static bool	connect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	connect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const QMetaMethod &signalMethod, const QObject receiver, const QMetaMethod &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, const QString &signalMethod, const QString &location, const QObject receiver, const QString &slotMethod)

static bool	disconnect (const QObject sender, std::nullptr_t, const QObject receiver, std::nullptr_t)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver receiver, SlotReturn (SlotClass::slotMethod)(SlotArgs...))

template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)

template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool	disconnect (const Sender sender, void (SignalClass::signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)

static QMetaObject &	staticMetaObject ()

static QString	tr (const char text, const char comment=nullptr, std::optional< int > numArg=std::optional< int >())

Properties inherited from QObject
	objectName

Related Functions inherited from QObject
T	qobject_cast (QObject *object)

	QObjectList

Detailed Description

The QSaveFile class provides an interface for safely writing to files. QSaveFile is an I/O device for writing text and binary files, without losing existing data if the writing operation fails.

The contents will be written to a temporary file. If no error occurs commit() will rename the temporary file to the final name. This ensures that no data at the final file is lost in case an error happens while writing, and no partially-written file is ever present at the final location. Always use QSaveFile when saving entire documents to disk.

QSaveFile automatically detects errors while writing, such as the full partition situation, where write() can not write all the bytes. It will remember that an error happened, and will discard the temporary file in commit().

Much like QFile, the file is opened with open(). Data is usually read and written using QDataStream or QTextStream, you can also call the QIODevice methods read(), readLine(), readAll(), and write(). Unlike QFile calling close() is not allowed. commit() replaces it. If commit() was not called and the QSaveFile instance is destroyed, the temporary file is discarded.

To abort saving due to an application error, call cancelWriting() so that even a call to commit() later on will not save.

See also: QTextStream, QDataStream, QFileInfo, QDir, QFile, QTemporaryFile

Constructor & Destructor Documentation

QSaveFile::QSaveFile ( const QString & name )

explicit

Constructs a new file object to represent the file with the given name.

QSaveFile::QSaveFile ( QObject * parent = nullptr )

explicit

Constructs a new file object with the given parent.

QSaveFile::QSaveFile	(	const QString &	name,
		QObject *	parent
	)

explicit

Constructs a new file object with the given parent to represent the file with the specified name.

QSaveFile::~QSaveFile ( )

Destroys the file object discarding the saved contents unless commit() was called.

Method Documentation

void QSaveFile::cancelWriting ( )

Cancels writing the new file. If the application changes its mind while saving, it can call cancelWriting(), which sets an error code so that commit() will discard the temporary file. Alternatively, it can simply make sure not to call commit(). Further write operations are possible after calling this method, but none of it will have any effect, the written file will be discarded.

This method has no effect when direct write fallback is used. This is the case when saving over an existing file in a readonly directory: no temporary file can be created, so the existing file is overwritten no matter what, and cancelWriting() can not do anything about that, the contents of the existing file will be lost.

See also: commit()

bool QSaveFile::commit ( )

Commits the changes to disk, if all previous writes were successful. It is mandatory to call this at the end of the saving operation, otherwise the file will be discarded. If an error happened during writing, deletes the temporary file and returns false. Otherwise, renames it to the final fileName and returns true on success. Finally, closes the device.

See also: cancelWriting()

bool QSaveFile::directWriteFallback ( ) const

Returns true if the fallback solution for saving files in read only directories is enabled.

See also: setDirectWriteFallback()

QString QSaveFile::fileName ( ) const

overridevirtual

Returns the name set by setFileName() or by the QSaveFile constructor.

See also: setFileName()

Reimplemented from QFileDevice::fileName()

bool QSaveFile::open ( OpenMode mode )

overridevirtual

Opens the file using OpenMode mode, returning true if successful, otherwise false. The mode must include QIODevice::WriteOnly. It may also have additional flags, such as QIODevice::Text and QIODevice::Unbuffered.

QIODevice::ReadWrite and QIODevice::Append are not supported at the moment.

See also: QIODevice::OpenMode, setFileName()

Reimplemented from QIODevice::open()

void QSaveFile::setDirectWriteFallback ( bool enabled )

Allows writing over the existing file if necessary.

QSaveFile creates a temporary file in the same directory as the final file and atomically renames it. However this is not possible if the directory permissions do not allow creating new files. In order to preserve atomicity guarantees, open() fails when it can not create the temporary file.

In order to allow users to edit files with write permissions in a directory with restricted permissions, call setDirectWriteFallback() with enabled set to true, and the following calls to open() will fallback to opening the existing file directly and writing into it, without the use of a temporary file. This does not have atomicity guarantees, i.e. an application crash or for instance a power failure could lead to a partially-written file on disk. It also means cancelWriting() has no effect, in such a case.

Typically, to save documents edited by the user, call setDirectWriteFallback(true), and to save application internal files (configuration files, data files, etc), keep the default setting which ensures atomicity.

See also: directWriteFallback()

void QSaveFile::setFileName ( const QString & name )

Sets the name of the file. The name can have no path, a relative path, or an absolute path.

See also: QFile::setFileName(), fileName()

qint64 QSaveFile::writeData	(	const char *	data,
		qint64	len
	)

overrideprotectedvirtual

Reimplemented from QFileDevice::writeData()

Public Methods

Protected Methods

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Method Documentation