QtCore¶

The QtCore module contains the core classes, including the event loop and Qt’s signal and slot mechanism. It also includes platform independent abstractions for animations, state machines, threads, mapped files, shared memory, regular expressions, and user and application settings.

Classes¶

QAbstractAnimation	QFile	QMutexLocker	QStateMachine
QAbstractEventDispatcher	QFileDevice	QObject	QStorageInfo
QAbstractItemModel	QFileInfo	QObjectCleanupHandler	QStringListModel
QAbstractListModel	QFileSelector	QOperatingSystemVersion	QSysInfo
QAbstractNativeEventFilter	QFileSystemWatcher	QParallelAnimationGroup	QSystemSemaphore
QAbstractProxyModel	QFinalState	QPauseAnimation	Qt
QAbstractState	QGenericArgument	QPersistentModelIndex	QTemporaryDir
QAbstractTableModel	QGenericReturnArgument	QPluginLoader	QTemporaryFile
QAbstractTransition	QHistoryState	QPoint	QTextBoundaryFinder
QAnimationGroup	QIdentityProxyModel	QPointF	QTextCodec
QBasicTimer	QIODevice	QProcess	QTextDecoder
QBitArray	QItemSelection	QProcessEnvironment	QTextEncoder
QBuffer	QItemSelectionModel	QPropertyAnimation	QTextStream
QByteArray	QItemSelectionRange	QRandomGenerator	QThread
QByteArrayMatcher	QJsonDocument	QReadLocker	QThreadPool
QCalendar	QJsonParseError	QReadWriteLock	QTime
QCborError	QJsonValue	QRect	QTimeLine
QCborStreamReader	QLibrary	QRectF	QTimer
QCborStreamWriter	QLibraryInfo	QRecursiveMutex	QTimerEvent
QChildEvent	QLine	QRegExp	QTimeZone
QCollator	QLineF	QRegularExpression	QTranslator
QCollatorSortKey	QLocale	QRegularExpressionMatch	QTransposeProxyModel
QCommandLineOption	QLockFile	QRegularExpressionMatchIterator	QUrl
QCommandLineParser	QLoggingCategory	QResource	QUrlQuery
QConcatenateTablesProxyModel	QMargins	QRunnable	QUuid
QCoreApplication	QMarginsF	QSaveFile	QVariant
QCryptographicHash	QMessageAuthenticationCode	QSemaphore	QVariantAnimation
QDataStream	QMessageLogContext	QSemaphoreReleaser	QVersionNumber
QDate	QMessageLogger	QSequentialAnimationGroup	QWaitCondition
QDateTime	QMetaClassInfo	QSettings	QWinEventNotifier
QDeadlineTimer	QMetaEnum	QSharedMemory	QWriteLocker
QDir	QMetaMethod	QSignalBlocker	QXmlStreamAttribute
QDirIterator	QMetaObject	QSignalMapper	QXmlStreamAttributes
QDynamicPropertyChangeEvent	QMetaProperty	QSignalTransition	QXmlStreamEntityDeclaration
QEasingCurve	QMetaType	QSize	QXmlStreamEntityResolver
QElapsedTimer	QMimeData	QSizeF	QXmlStreamNamespaceDeclaration
QEvent	QMimeDatabase	QSocketNotifier	QXmlStreamNotationDeclaration
QEventLoop	QMimeType	QSortFilterProxyModel	QXmlStreamReader
QEventLoopLocker	QModelIndex	QStandardPaths	QXmlStreamWriter
QEventTransition	QMutex	QState

Enums¶

QCborKnownTags

TODO

Member	Value	Description
Base64	TODO	TODO
Base64url	TODO	TODO
Bigfloat	TODO	TODO
COSE_Encrypt	TODO	TODO
COSE_Encrypt0	TODO	TODO
COSE_Mac	TODO	TODO
COSE_Mac0	TODO	TODO
COSE_Sign	TODO	TODO
COSE_Sign1	TODO	TODO
DateTimeString	TODO	TODO
Decimal	TODO	TODO
EncodedCbor	TODO	TODO
ExpectedBase16	TODO	TODO
ExpectedBase64	TODO	TODO
ExpectedBase64url	TODO	TODO
MimeMessage	TODO	TODO
NegativeBignum	TODO	TODO
PositiveBignum	TODO	TODO
RegularExpression	TODO	TODO
Signature	TODO	TODO
UnixTime_t	TODO	TODO
Url	TODO	TODO
Uuid	TODO	TODO

QCborSimpleType

This enum contains the possible “Simple Types” for CBOR. Simple Types range from 0 to 255 and are types that carry no further value.

The following values are currently known:

Qt CBOR API supports encoding and decoding any Simple Type, whether one of those above or any other value.

Applications should only use further values if a corresponding specification has been published, otherwise interpretation and validation by the remote may fail. Values 24 to 31 are reserved and must not be used.

The current authoritative list is maintained by IANA in the Simple Values registry.

See also

QCborValue::isSimpleType(), QCborValue::toSimpleType(), QCborStreamWriter::append(QCborSimpleType)QCborStreamReader::isSimpleType()QCborStreamReader::toSimpleType().

Member	Value	Description
False_	TODO	TODO
Null	TODO	Absence of value (null).
True_	TODO	TODO
Undefined	TODO	Missing or deleted value, usually an error.

QtMsgType

This enum describes the messages that can be sent to a message handler (QtMessageHandler). You can use the enum to identify and associate the various message types with the appropriate actions.

QtInfoMsg was added in Qt 5.5.

See also

QtMessageHandler.

Member	Value	Description
QtCriticalMsg	2	A message generated by the qCritical() function.
QtDebugMsg	0	A message generated by the qDebug() function.
QtFatalMsg	3	A message generated by the qFatal() function.
QtInfoMsg	TODO	A message generated by the qInfo() function.
QtSystemMsg	TODO	TODO
QtWarningMsg	1	A message generated by the qWarning() function.

Attributes¶

PYQT_VERSION: int

This is a read-only attribute.

TODO

PYQT_VERSION_STR: str

This is a read-only attribute.

TODO

QT_VERSION: int

This is a read-only attribute.

This macro expands a numeric value of the form 0xMMNNPP (MM = major, NN = minor, PP = patch) that specifies Qt’s version number. For example, if you compile your application against Qt 4.1.2, the macro will expand to 0x040102.

You can use to use the latest Qt features where available.

Example:

# #if QT_VERSION >= 0x040100
#     QIcon icon = style()->standardIcon(QStyle::SP_TrashIcon);
# #else
#     QPixmap pixmap = style()->standardPixmap(QStyle::SP_TrashIcon);
#     QIcon icon(pixmap);
# #endif

See also

QT_VERSION_STR.

QT_VERSION_STR: str

This is a read-only attribute.

This macro expands to a string that specifies Qt’s version number (for example, “4.1.2”). This is the version against which the application is compiled.

See also

QT_VERSION, qVersion().

Functions¶

bin_(QTextStream) → QTextStream: Calls setIntegerBase()(2) on stream and returns stream.

See also

oct_(), dec(), hex_(), QTextStream manipulators.

bom(QTextStream) → QTextStream: Toggles insertion of the Byte Order Mark on stream when QTextStream is used with a UTF codec.

See also

setGenerateByteOrderMark(), QTextStream manipulators.

center(QTextStream) → QTextStream: Calls setFieldAlignment()(AlignCenter) on stream and returns stream.

See also

left(), right(), QTextStream manipulators.

dec(QTextStream) → QTextStream: Calls setIntegerBase()(10) on stream and returns stream.

See also

bin_(), oct_(), hex_(), QTextStream manipulators.

endl(QTextStream) → QTextStream

Writes ‘\n’ to the stream and flushes the stream.

Equivalent to

# stream << '\n' << flush;

Note: On Windows, all ‘\n’ characters are written as ‘\r\n’ if QTextStream’s device or string is opened using the Text flag.

fixed(QTextStream) → QTextStream: Calls setRealNumberNotation()(FixedNotation) on stream and returns stream.

See also

scientific(), QTextStream manipulators.

flush(QTextStream) → QTextStream: Calls flush() on stream and returns stream.

See also

endl(), reset(), QTextStream manipulators.

forcepoint(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() | ForcePoint) on stream and returns stream.

See also

noforcepoint(), forcesign(), showbase(), QTextStream manipulators.

forcesign(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() | ForceSign) on stream and returns stream.

See also

noforcesign(), forcepoint(), showbase(), QTextStream manipulators.

hex_(QTextStream) → QTextStream

Calls setIntegerBase()(16) on stream and returns stream.

Note: The hex modifier can only be used for writing to streams.

left(QTextStream) → QTextStream: Calls setFieldAlignment()(AlignLeft) on stream and returns stream.

See also

right(), center(), QTextStream manipulators.

lowercasebase(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() & ~UppercaseBase) on stream and returns stream.

See also

uppercasebase(), lowercasedigits(), QTextStream manipulators.

lowercasedigits(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() & ~UppercaseDigits) on stream and returns stream.

See also

uppercasedigits(), lowercasebase(), QTextStream manipulators.

noforcepoint(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() & ~ForcePoint) on stream and returns stream.

See also

forcepoint(), noforcesign(), noshowbase(), QTextStream manipulators.

noforcesign(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() & ~ForceSign) on stream and returns stream.

See also

forcesign(), noforcepoint(), noshowbase(), QTextStream manipulators.

noshowbase(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() & ~ShowBase) on stream and returns stream.

See also

showbase(), noforcesign(), noforcepoint(), QTextStream manipulators.

oct_(QTextStream) → QTextStream: Calls setIntegerBase()(8) on stream and returns stream.

See also

bin_(), dec(), hex_(), QTextStream manipulators.

pyqtPickleProtocol() → Optional[int]: TODO

pyqtRemoveInputHook(): TODO

pyqtRestoreInputHook(): TODO

pyqtSetPickleProtocol(Optional[int]): TODO

pyqtSlot(..., name: str = None, result: str = None) → Callable[..., Optional[str]]: TODO

Q_ARG(object, object) → QGenericArgument: This macro takes a Type and a value of that type and returns a QGenericArgument object that can be passed to invokeMethod().

See also

Q_RETURN_ARG().

Q_CLASSINFO(str, str)

This macro associates extra information to the class, which is available using metaObject(). Qt makes only limited use of this feature, in the Active Qt, Qt D-Bus and Qt QML.

The extra information takes the form of a Name string and a Value literal string.

Example:

# class MyClass : public QObject
# {
#     Q_OBJECT
#     Q_CLASSINFO("Author", "Pierre Gendron")
#     Q_CLASSINFO("URL", "http://www.my-organization.qc.ca")

# public:
#     ...
# };

Q_ENUM(Union[type, enum.Enum])

This macro registers an enum type with the meta-object system. It must be placed after the enum declaration in a class that has the Q_OBJECT or the Q_GADGET macro. For namespaces use Q_ENUM_NS() instead.

For example:

# class MyClass : public QObject
# {
#     Q_OBJECT

# public:
#     MyClass(QObject *parent = 0);
#     ~MyClass();

#     enum Priority { High, Low, VeryHigh, VeryLow };
#     Q_ENUM(Priority)
#     void setPriority(Priority priority);
#     Priority priority() const;
# };

Enumerations that are declared with have their QMetaEnum registered in the enclosing QMetaObject. You can also use QMetaEnum::fromType() to get the QMetaEnum.

Registered enumerations are automatically registered also to the Qt meta type system, making them known to QMetaType without the need to use Q_DECLARE_METATYPE(). This will enable useful features; for example, if used in a QVariant, you can convert them to strings. Likewise, passing them to QDebug will print out their names.

See also

Qt’s Property System.

Q_ENUMS(...)

This macro registers one or several enum types to the meta-object system.

For example:

# class MyClass : public QObject
# {
#     Q_OBJECT

# public:
#     MyClass(QObject *parent = 0);
#     ~MyClass();

#     enum Priority { High, Low, VeryHigh, VeryLow };
#     Q_ENUM(Priority)
#     void setPriority(Priority priority);
#     Priority priority() const;
# };

If you want to register an enum that is declared in another class, the enum must be fully qualified with the name of the class defining it. In addition, the class defining the enum has to inherit QObject as well as declare the enum using .

In new code, you should prefer the use of the Q_ENUM() macro, which makes the type available also to the meta type system. For instance, QMetaEnum::fromType() will not work with types declared with .

See also

Qt’s Property System.

Q_FLAG(Union[type, enum.Enum])

This macro registers a single flags type with the meta-object system. It is typically used in a class definition to declare that values of a given enum can be used as flags and combined using the bitwise OR operator. For namespaces use Q_FLAG_NS() instead.

The macro must be placed after the enum declaration.

For example, in QLibrary, the LoadHints flag is declared in the following way:

# class QLibrary : public QObject
# {
#     Q_OBJECT

# public:
#     ...

#     enum LoadHint {
#         ResolveAllSymbolsHint = 0x01,
#         ExportExternalSymbolsHint = 0x02,
#         LoadArchiveMemberHint = 0x04
#     };
#     Q_DECLARE_FLAGS(LoadHints, LoadHint)
#     Q_FLAG(LoadHints)
#     ...
# }

The declaration of the flags themselves is performed in the public section of the QLibrary class itself, using the Q_DECLARE_FLAGS() macro.

Note: The macro takes care of registering individual flag values with the meta-object system, so it is unnecessary to use Q_ENUM() in addition to this macro.

See also

Qt’s Property System.

Q_FLAGS(...)

This macro registers one or several flags types with the meta-object system. It is typically used in a class definition to declare that values of a given enum can be used as flags and combined using the bitwise OR operator.

Note: This macro takes care of registering individual flag values with the meta-object system, so it is unnecessary to use Q_ENUMS() in addition to this macro.

In new code, you should prefer the use of the Q_FLAG() macro, which makes the type available also to the meta type system.

See also

Qt’s Property System.

Q_RETURN_ARG(object) → QGenericReturnArgument: This macro takes a Type and a non-const reference to a value of that type and returns a QGenericReturnArgument object that can be passed to invokeMethod().

See also

Q_ARG().

qAbs(float) → float: TODO

qAddPostRoutine(callable): TODO

qAddPreRoutine(Callable[[], None]): TODO

qChecksum(bytes) → int

Returns the CRC-16 checksum of the first len bytes of data.

The checksum is independent of the byte order (endianness) and will be calculated accorded to the algorithm published in ISO 3309 (Qt::ChecksumIso3309).

Note: This function is a 16-bit cache conserving (16 entry table) implementation of the CRC-16-CCITT algorithm.

qChecksum(bytes, ChecksumType) → int: TODO

qCompress(Union[QByteArray, bytes, bytearray], compressionLevel: int = -1) → QByteArray: TODO

qCritical(str)

Calls the message handler with the critical message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

It exits if the environment variable QT_FATAL_CRITICALS is not empty.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

# void load(const QString &fileName)
# {
#     QFile file(fileName);
#     if (!file.exists())
#         qCritical("File '%s' does not exist!", qUtf8Printable(fileName));
# }

If you include <QtDebug>, a more convenient syntax is also available:

# qCritical() << "Brush:" << myQBrush << "Other
# value:" << i;

A space is inserted between the items, and a newline is appended at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

qDebug(str): TODO

qEnvironmentVariable(str) → str: TODO

qEnvironmentVariable(str, str) → str: TODO

qErrnoWarning(str): TODO

qErrnoWarning(int, str): TODO

qFatal(str)

Calls the message handler with the fatal message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

If you are using the default message handler this function will abort to create a core dump. On Windows, for debug builds, this function will report a _CRT_ERROR enabling you to connect a debugger to the application.

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

# int divide(int a, int b)
# {
#     if (b == 0)                                // program error
#         qFatal("divide: cannot divide by zero");
#     return a / b;
# }

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

qFloatDistance(float, float) → int

Returns the number of representable floating-point numbers between a and b.

This function serves the same purpose as qFloatDistance(float, float), but returns the distance between two double numbers. Since the range is larger than for two float numbers ([-DBL_MAX,DBL_MAX]), the return type is quint64.

See also

qFuzzyCompare().

qFormatLogMessage(QtMsgType, QMessageLogContext, str) → str: TODO

qFuzzyCompare(float, float) → bool

Compares the floating point value p1 and p2 and returns true if they are considered equal, otherwise false.

Note that comparing values where either p1 or p2 is 0.0 will not work, nor does comparing values where one of the values is NaN or infinity. If one of the values is always 0.0, use qFuzzyIsNull instead. If one of the values is likely to be 0.0, one solution is to add 1.0 to both values.

#         // Instead of comparing with 0.0
#                 qFuzzyCompare(0.0,1.0e-200); // This will return false
#         // Compare adding 1 to both values will fix the problem
#                 qFuzzyCompare(1 + 0.0, 1 + 1.0e-200); // This will return true

The two numbers are compared in a relative way, where the exactness is stronger the smaller the numbers are.

qInf() → float: Returns the bit pattern for an infinite number as a double.

qInfo(str)

Calls the message handler with the informational message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the console, if it is a console application; otherwise, it is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_INFO_OUTPUT was defined during compilation.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.

Example:

# qInfo("Items in list: %d", myList.size());

If you include <QtDebug>, a more convenient syntax is also available:

# qInfo() << "Brush:" << myQBrush << "Other value:" << i;

With this syntax, the function returns a QDebug object that is configured to use the QtInfoMsg message type. It automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

To suppress the output at run-time, install your own message handler with qInstallMessageHandler().

qInstallMessageHandler(Optional[Callable[[QtMsgType, QMessageLogContext, str], None]]) → Optional[Callable[[QtMsgType, QMessageLogContext, str], None]]: TODO

qIsFinite(float) → bool: Returns true if the double d is a finite number.

qIsInf(float) → bool: Returns true if the double d is equivalent to infinity.

qIsNaN(float) → bool: Returns true if the double d is not a number (NaN).

qIsNull(float) → bool: TODO

qQNaN() → float: Returns the bit pattern of a quiet NaN as a double.

qrand() → int: TODO

qRegisterResourceData(int, bytes, bytes, bytes) → bool: TODO

qRemovePostRoutine(callable): TODO

qRound(float) → int: TODO

qRound64(float) → int: TODO

qSetFieldWidth(int) → QTextStreamManipulator: Equivalent to setFieldWidth()(width).

qSetMessagePattern(str): TODO

qSetPadChar(str) → QTextStreamManipulator: TODO

qSetRealNumberPrecision(int) → QTextStreamManipulator: Equivalent to setRealNumberPrecision()(precision).

qSharedBuild() → bool: TODO

qSNaN() → float: Returns the bit pattern of a signalling NaN as a double.

qsrand(int): TODO

QT_TR_NOOP(str) → str

Marks the UTF-8 encoded string literal sourceText for delayed translation in the current context (class).

The macro tells lupdate to collect the string, and expands to sourceText itself.

Example:

# QString FriendlyConversation::greeting(int type)
# {
#     static const char *greeting_strings[] = {
#         QT_TR_NOOP("Hello"),
#         QT_TR_NOOP("Goodbye")
#     };
#     return tr(greeting_strings[type]);
# }

The macro QT_TR_NOOP_UTF8() is identical and obsolete; this applies to all other _UTF8 macros as well.

See also

QT_TRANSLATE_NOOP().

QT_TR_NOOP_UTF8(str) → str: TODO

QT_TRANSLATE_NOOP(str, str) → str

Marks the UTF-8 encoded string literal sourceText for delayed translation in the given context. The context is typically a class name and also needs to be specified as a string literal.

The macro tells lupdate to collect the string, and expands to sourceText itself.

Example:

# static const char *greeting_strings[] = {
#     QT_TRANSLATE_NOOP("FriendlyConversation", "Hello"),
#     QT_TRANSLATE_NOOP("FriendlyConversation", "Goodbye")
# };

# QString FriendlyConversation::greeting(int type)
# {
#     return tr(greeting_strings[type]);
# }

# QString global_greeting(int type)
# {
#     return qApp->translate("FriendlyConversation",
#                            greeting_strings[type]);
# }

See also

QT_TR_NOOP(), QT_TRANSLATE_NOOP3().

qUncompress(Union[QByteArray, bytes, bytearray]) → QByteArray: TODO

qUnregisterResourceData(int, bytes, bytes, bytes) → bool: TODO

qVersion() → str: TODO

qWarning(str)

Calls the message handler with the warning message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_WARNING_OUTPUT was defined during compilation; it exits if at the nth warning corresponding to the counter in environment variable QT_FATAL_WARNINGS. That is, if the environment variable contains the value 1, it will exit on the 1st message; if it contains the value 10, it will exit on the 10th message. Any non-numeric value is equivalent to 1.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

# void f(int c)
# {
#     if (c > 200)
#         qWarning("f: bad argument, c == %d", c);
# }

If you include <QtDebug>, a more convenient syntax is also available:

# qWarning() << "Brush:" << myQBrush << "Other value:"
# << i;

This syntax inserts a space between each item, and appends a newline at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

reset(QTextStream) → QTextStream: Calls reset() on stream and returns stream.

See also

flush(), QTextStream manipulators.

right(QTextStream) → QTextStream: Calls setFieldAlignment()(AlignRight) on stream and returns stream.

See also

left(), center(), QTextStream manipulators.

scientific(QTextStream) → QTextStream: Calls setRealNumberNotation()(ScientificNotation) on stream and returns stream.

See also

fixed(), QTextStream manipulators.

showbase(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() | ShowBase) on stream and returns stream.

See also

noshowbase(), forcesign(), forcepoint(), QTextStream manipulators.

uppercasebase(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() | UppercaseBase) on stream and returns stream.

See also

lowercasebase(), uppercasedigits(), QTextStream manipulators.

uppercasedigits(QTextStream) → QTextStream: Calls setNumberFlags()(numberFlags() | UppercaseDigits) on stream and returns stream.

See also

lowercasedigits(), uppercasebase(), QTextStream manipulators.

ws(QTextStream) → QTextStream: Calls skipWhiteSpace() on stream and returns stream.

See also

QTextStream manipulators.