QVariant Class

Because QVariant is part of the Qt Core module, it cannot provide conversion functions to data types defined in Qt GUI, such as QColor, QImage, and QPixmap. In other words, there is no toColor() function. Instead, you can use the QVariant::value() or the qvariant_cast() template function. For example:

QVariant variant;
...
QColor color = variant.value<QColor>();

The inverse conversion (e.g., from QColor to QVariant) is automatic for all data types supported by QVariant, including GUI-related types:

QColor color = palette().background().color();
QVariant variant = color;

When using canConvert() and convert() consecutively, it is possible for canConvert() to return true, but convert() to return false. This is typically because canConvert() only reports the general ability of QVariant to convert between types given suitable data; it is still possible to supply data which cannot actually be converted.

For example, canConvert(QMetaType::fromType<int>()) would return true when called on a variant containing a string because, in principle, QVariant is able to convert strings of numbers to integers. However, if the string contains non-numeric characters, it cannot be converted to an integer, and any attempt to convert it will fail. Hence, it is important to have both functions return true for a successful conversion.

See also QMetaType

int QVariant::userType() const

Returns the storage type of the value stored in the variant. This is the same as metaType().id().

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const void *QVariant::data() const

Returns a pointer to the contained object as a generic void* that cannot be written to.

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Constructs an invalid variant.

Constructs variant of type type, and initializes with copy if copy is not nullptr.

Note that you have to pass the address of the variable you want stored.

Usually, you never have to use this constructor, use QVariant::fromValue() instead to construct variants from the pointer types represented by QMetaType::VoidStar, and QMetaType::QObjectStar.

If type does not support copy and default construction, the variant will be invalid.

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Constructs a new variant with an easing curve value, val.

Constructs a new variant with a json document value, val.

This function was introduced in Qt 5.0.

Constructs a new variant with a QPersistentModelIndex value, val.

This function was introduced in Qt 5.5.

Constructs a new variant with a string value of val. The variant creates a deep copy of val into a QString assuming UTF-8 encoding on the input val.

Note that val is converted to a QString for storing in the variant and QVariant::userType() will return QMetaType::QString for the variant.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications.

Constructs a new variant with a string value, val.

Constructs a new variant with an uuid value, val.

This function was introduced in Qt 5.0.

Constructs a new variant with a point value of val.

Constructs a new variant with a point value of val.

Constructs a new variant with a rect value of val.

Constructs a new variant with a line value of val.

Constructs a new variant with a line value of val.

Constructs a new variant with a rect value of val.

Constructs a new variant with a size value of val.

Constructs a new variant with a size value of val.

Constructs a new variant with an integer value, val.

Constructs a new variant with an unsigned integer value, val.

Constructs a new variant with a long long integer value, val.

Constructs a new variant with an unsigned long long integer value, val.

Constructs a new variant with a boolean value, val.

Constructs a new variant with a floating point value, val.

Constructs a new variant with a floating point value, val.

Constructs a new variant with a char value, c.

Constructs a new variant with a date value, val.

Constructs a new variant with a time value, val.

Constructs a new variant with a bitarray value, val.

Constructs a new variant with a bytearray value, val.

Constructs a new variant with a date/time value, val.

Constructs a new variant with a hash of QVariants, val.

Constructs a new variant with a json array value, val.

This function was introduced in Qt 5.0.

Constructs a new variant with a json object value, val.

This function was introduced in Qt 5.0.

Constructs a new variant with a list value, val.

Constructs a new variant with a locale value, l.

Constructs a new variant with a map of QVariants, val.

Constructs a new variant with the regular expression value re.

This function was introduced in Qt 5.0.

Constructs a new variant with a string value, val.

Constructs a new variant with a string list value, val.

Constructs a new variant with a url value of val.

Constructs a new variant with a json value, val.

This function was introduced in Qt 5.0.

Constructs a new variant with a QModelIndex value, val.

This function was introduced in Qt 5.0.

Constructs a copy of the variant, p, passed as the argument to this constructor.

Move-constructs a QVariant instance, making it point at the same object that other was pointing to.

This function was introduced in Qt 5.2.

Destroys the QVariant and the contained object.

Note that subclasses that reimplement clear() should reimplement the destructor to call clear(). This destructor calls clear(), but because it is the destructor, QVariant::clear() is called rather than a subclass's clear().

Returns true if the variant's type can be cast to the requested type, type. Such casting is done automatically when calling the toInt(), toBool(), ... methods.

This function was introduced in Qt 6.0.

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Returns true if the variant can be converted to the template type T, otherwise false.

Example:

QVariant v = 42;

v.canConvert<int>();              // returns true
v.canConvert<QString>();          // returns true

MyCustomStruct s;
v.setValue(s);

v.canConvert<int>();              // returns false
v.canConvert<MyCustomStruct>();   // returns true

A QVariant containing a pointer to a type derived from QObject will also return true for this function if a qobject_cast to the template type T would succeed. Note that this only works for QObject subclasses which use the Q_OBJECT macro.

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Returns true if a mutable view of the template type T can be created on this variant, otherwise false.

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Convert this variant to type QMetaType::UnknownType and free up any resources used.

Compares the objects at lhs and rhs for ordering.

Returns QPartialOrdering::Unordered if comparison is not supported or the values are unordered. Otherwise, returns QPartialOrdering::Less, QPartialOrdering::Equivalent or QPartialOrdering::Greater if lhs is less than, equivalent to or greater than rhs, respectively.

If the variants contain data with a different metatype, the values are considered unordered unless they are both of numeric or pointer types, where regular numeric or pointer comparison rules will be used.

If both variants contain data of the same metatype, the method will use the QMetaType::compare method to determine the ordering of the two variants, which can also indicate that it can't establish an ordering between the two values.

This function was introduced in Qt 6.0.

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Casts the variant to the requested type, targetType. If the cast cannot be done, the variant is still changed to the requested type, but is left in a cleared null state similar to that constructed by QVariant(Type).

Returns true if the current type of the variant was successfully cast; otherwise returns false.

A QVariant containing a pointer to a type derived from QObject will also convert and return true for this function if a qobject_cast to the type described by targetType would succeed. Note that this only works for QObject subclasses which use the Q_OBJECT macro.

This function was introduced in Qt 6.0.

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Returns a pointer to the contained object as a generic void* that can be written to.

This function detaches the QVariant. When called on a null-QVariant, the QVariant will not be null after the call.

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Returns a QVariant with the type and value of the active variant of value. If the active type is std::monostate a default QVariant is returned.

This function was introduced in Qt 5.11.

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Returns a QVariant containing a copy of value. Behaves exactly like setValue() otherwise.

Example:

MyCustomStruct s;
return QVariant::fromValue(s);

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Returns true if this is a null variant, false otherwise.

A variant is considered null if it contains no initialized value or a null pointer.

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Returns true if the storage type of this variant is not QMetaType::UnknownType; otherwise returns false.

Returns the QMetaType of the value stored in the variant.

This function was introduced in Qt 6.0.

Stores a copy of value. If T is a type that QVariant doesn't support, QMetaType is used to store the value. A compile error will occur if QMetaType doesn't handle the type.

Example:

QVariant v;

v.setValue(5);
int i = v.toInt();         // i is now 5
QString s = v.toString();  // s is now "5"

MyCustomStruct c;
v.setValue(c);

...

MyCustomStruct c2 = v.value<MyCustomStruct>();

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Copies value over this QVariant. It is equivalent to simply assigning value to this QVariant.

Moves value over this QVariant. It is equivalent to simply move assigning value to this QVariant.

Swaps variant other with this variant. This operation is very fast and never fails.

Returns the variant as a QBitArray if the variant has userType() QMetaType::QBitArray; otherwise returns an empty bit array.

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Returns the variant as a bool if the variant has userType() Bool.

Returns true if the variant has userType() QMetaType::Bool, QMetaType::QChar, QMetaType::Double, QMetaType::Int, QMetaType::LongLong, QMetaType::UInt, or QMetaType::ULongLong and the value is non-zero, or if the variant has type QMetaType::QString or QMetaType::QByteArray and its lower-case content is not one of the following: empty, "0" or "false"; otherwise returns false.

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Returns the variant as a QByteArray if the variant has userType() QMetaType::QByteArray or QMetaType::QString (converted using QString::fromUtf8()); otherwise returns an empty byte array.

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Returns the variant as a QChar if the variant has userType() QMetaType::QChar, QMetaType::Int, or QMetaType::UInt; otherwise returns an invalid QChar.

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Returns the variant as a QDate if the variant has userType() QMetaType::QDate, QMetaType::QDateTime, or QMetaType::QString; otherwise returns an invalid date.

If the type() is QMetaType::QString, an invalid date will be returned if the string cannot be parsed as a Qt::ISODate format date.

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Returns the variant as a QDateTime if the variant has userType() QMetaType::QDateTime, QMetaType::QDate, or QMetaType::QString; otherwise returns an invalid date/time.

If the type() is QMetaType::QString, an invalid date/time will be returned if the string cannot be parsed as a Qt::ISODate format date/time.

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Returns the variant as a double if the variant has userType() QMetaType::Double, QMetaType::Float, QMetaType::Bool, QMetaType::QByteArray, QMetaType::Int, QMetaType::LongLong, QMetaType::QString, QMetaType::UInt, or QMetaType::ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

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Returns the variant as a QEasingCurve if the variant has userType() QMetaType::QEasingCurve; otherwise returns a default easing curve.

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Returns the variant as a float if the variant has userType() QMetaType::Double, QMetaType::Float, QMetaType::Bool, QMetaType::QByteArray, QMetaType::Int, QMetaType::LongLong, QMetaType::QString, QMetaType::UInt, or QMetaType::ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

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Returns the variant as a QHash<QString, QVariant> if the variant has type() QMetaType::QVariantHash; otherwise returns an empty map.

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Returns the variant as an int if the variant has userType() QMetaType::Int, QMetaType::Bool, QMetaType::QByteArray, QMetaType::QChar, QMetaType::Double, QMetaType::LongLong, QMetaType::QString, QMetaType::UInt, or QMetaType::ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

Warning: If the value is convertible to a QMetaType::LongLong but is too large to be represented in an int, the resulting arithmetic overflow will not be reflected in ok. A simple workaround is to use QString::toInt().

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Returns the variant as a QJsonArray if the variant has userType() QJsonArray; otherwise returns a default constructed QJsonArray.

This function was introduced in Qt 5.0.

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Returns the variant as a QJsonDocument if the variant has userType() QJsonDocument; otherwise returns a default constructed QJsonDocument.

This function was introduced in Qt 5.0.

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Returns the variant as a QJsonObject if the variant has userType() QJsonObject; otherwise returns a default constructed QJsonObject.

This function was introduced in Qt 5.0.

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Returns the variant as a QJsonValue if the variant has userType() QJsonValue; otherwise returns a default constructed QJsonValue.

This function was introduced in Qt 5.0.

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Returns the variant as a QLine if the variant has userType() QMetaType::QLine; otherwise returns an invalid QLine.

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Returns the variant as a QLineF if the variant has userType() QMetaType::QLineF; otherwise returns an invalid QLineF.

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Returns the variant as a QVariantList if the variant has userType() QMetaType::QVariantList. If it doesn't, QVariant will attempt to convert the type to a list and then return it. This will succeed for any type that has registered a converter to QVariantList or which was declared as a sequential container using Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE. If none of those conditions are true, this function will return an empty list.

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Returns the variant as a QLocale if the variant has userType() QMetaType::QLocale; otherwise returns an invalid QLocale.

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Returns the variant as a long long int if the variant has userType() QMetaType::LongLong, QMetaType::Bool, QMetaType::QByteArray, QMetaType::QChar, QMetaType::Double, QMetaType::Int, QMetaType::QString, QMetaType::UInt, or QMetaType::ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

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Returns the variant as a QVariantMap if the variant has type() QMetaType::QVariantMap. If it doesn't, QVariant will attempt to convert the type to a map and then return it. This will succeed for any type that has registered a converter to QVariantMap or which was declared as a associative container using Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE. If none of those conditions are true, this function will return an empty map.

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Returns the variant as a QModelIndex if the variant has userType() QModelIndex; otherwise returns a default constructed QModelIndex.

This function was introduced in Qt 5.0.

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Returns the variant as a QPersistentModelIndex if the variant has userType() QPersistentModelIndex; otherwise returns a default constructed QPersistentModelIndex.

This function was introduced in Qt 5.5.

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Returns the variant as a QPoint if the variant has userType() QMetaType::QPoint or QMetaType::QPointF; otherwise returns a null QPoint.

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Returns the variant as a QPointF if the variant has userType() QMetaType::QPoint or QMetaType::QPointF; otherwise returns a null QPointF.

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Returns the variant as a qreal if the variant has userType() QMetaType::Double, QMetaType::Float, QMetaType::Bool, QMetaType::QByteArray, QMetaType::Int, QMetaType::LongLong, QMetaType::QString, QMetaType::UInt, or QMetaType::ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

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Returns the variant as a QRect if the variant has userType() QMetaType::QRect; otherwise returns an invalid QRect.

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Returns the variant as a QRectF if the variant has userType() QMetaType::QRect or QMetaType::QRectF; otherwise returns an invalid QRectF.

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Returns the variant as a QRegularExpression if the variant has userType() QRegularExpression; otherwise returns an empty QRegularExpression.

This function was introduced in Qt 5.0.

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Returns the variant as a QSize if the variant has userType() QMetaType::QSize; otherwise returns an invalid QSize.

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Returns the variant as a QSizeF if the variant has userType() QMetaType::QSizeF; otherwise returns an invalid QSizeF.

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Returns the variant as a QString if the variant has a userType() including, but not limited to:

QMetaType::QString, QMetaType::Bool, QMetaType::QByteArray, QMetaType::QChar, QMetaType::QDate, QMetaType::QDateTime, QMetaType::Double, QMetaType::Int, QMetaType::LongLong, QMetaType::QStringList, QMetaType::QTime, QMetaType::UInt, or QMetaType::ULongLong.

Calling QVariant::toString() on an unsupported variant returns an empty string.

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Returns the variant as a QStringList if the variant has userType() QMetaType::QStringList, QMetaType::QString, or QMetaType::QVariantList of a type that can be converted to QString; otherwise returns an empty list.

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Returns the variant as a QTime if the variant has userType() QMetaType::QTime, QMetaType::QDateTime, or QMetaType::QString; otherwise returns an invalid time.

If the type() is QMetaType::QString, an invalid time will be returned if the string cannot be parsed as a Qt::ISODate format time.

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Returns the variant as an unsigned int if the variant has userType() QMetaType::UInt, QMetaType::Bool, QMetaType::QByteArray, QMetaType::QChar, QMetaType::Double, QMetaType::Int, QMetaType::LongLong, QMetaType::QString, or QMetaType::ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an unsigned int; otherwise *ok is set to false.

Warning: If the value is convertible to a QMetaType::ULongLong but is too large to be represented in an unsigned int, the resulting arithmetic overflow will not be reflected in ok. A simple workaround is to use QString::toUInt().

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Returns the variant as an unsigned long long int if the variant has type() QMetaType::ULongLong, QMetaType::Bool, QMetaType::QByteArray, QMetaType::QChar, QMetaType::Double, QMetaType::Int, QMetaType::LongLong, QMetaType::QString, or QMetaType::UInt; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

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Returns the variant as a QUrl if the variant has userType() QMetaType::QUrl; otherwise returns an invalid QUrl.

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Returns the variant as a QUuid if the variant has type() QMetaType::QUuid, QMetaType::QByteArray or QMetaType::QString; otherwise returns a default-constructed QUuid.

This function was introduced in Qt 5.0.

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Returns the name of the type stored in the variant. The returned strings describe the C++ datatype used to store the data: for example, "QFont", "QString", or "QVariantList". An Invalid variant returns 0.

Returns the stored value converted to the template type T. Call canConvert() to find out whether a type can be converted. If the value cannot be converted, a default-constructed value will be returned.

If the type T is supported by QVariant, this function behaves exactly as toString(), toInt() etc.

Example:

QVariant v;

MyCustomStruct c;
if (v.canConvert<MyCustomStruct>())
    c = v.value<MyCustomStruct>();

v = 7;
int i = v.value<int>();                        // same as v.toInt()
QString s = v.value<QString>();                // same as v.toString(), s is now "7"
MyCustomStruct c2 = v.value<MyCustomStruct>(); // conversion failed, c2 is empty

If the QVariant contains a pointer to a type derived from QObject then T may be any QObject type. If the pointer stored in the QVariant can be qobject_cast to T, then that result is returned. Otherwise nullptr is returned. Note that this only works for QObject subclasses which use the Q_OBJECT macro.

If the QVariant contains a sequential container and T is QVariantList, the elements of the container will be converted into QVariants and returned as a QVariantList.

QList<int> intList = {7, 11, 42};

QVariant variant = QVariant::fromValue(intList);
if (variant.canConvert<QVariantList>()) {
    QSequentialIterable iterable = variant.value<QSequentialIterable>();
    // Can use foreach:
    foreach (const QVariant &v, iterable) {
        qDebug() << v;
    }
    // Can use C++11 range-for:
    for (const QVariant &v : iterable) {
        qDebug() << v;
    }
    // Can use iterators:
    QSequentialIterable::const_iterator it = iterable.begin();
    const QSequentialIterable::const_iterator end = iterable.end();
    for ( ; it != end; ++it) {
        qDebug() << *it;
    }
}

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Returns a mutable view of template type T on the stored value. Call canView() to find out whether such a view is supported. If no such view can be created, returns the stored value converted to the template type T. Call canConvert() to find out whether a type can be converted. If the value can neither be viewed nor converted, a default-constructed value will be returned.

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Assigns the value of the variant variant to this variant.

Move-assigns other to this QVariant instance.

This function was introduced in Qt 5.2.

Synonym for QHash<QString, QVariant>.

Synonym for QList<QVariant>.

Synonym for QMap<QString, QVariant>.

Returns the given value converted to the template type T.

This function is equivalent to QVariant::value().

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Returns false if v1 and v2 are equal; otherwise returns true.

QVariant uses the equality operator of the type() contained to check for equality.

Variants of different types will always compare as not equal with a few exceptions:

• If both types are numeric types (integers and floatins point numbers) Qt will compare those types using standard C++ type promotion rules.

• If one type is numeric and the other one a QString, Qt will try to convert the QString to a matching numeric type and if successful compare those.

• If both variants contain pointers to QObject derived types, QVariant will check whether the types are related and point to the same object.

Writes a variant p to the stream s.

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Returns true if v1 and v2 are equal; otherwise returns false.

QVariant uses the equality operator of the type() contained to check for equality.

Variants of different types will always compare as not equal with a few exceptions:

• If both types are numeric types (integers and floatins point numbers) Qt will compare those types using standard C++ type promotion rules.

• If one type is numeric and the other one a QString, Qt will try to convert the QString to a matching numeric type and if successful compare those.

• If both variants contain pointers to QObject derived types, QVariant will check whether the types are related and point to the same object.

The result of the function is not affected by the result of QVariant::isNull, which means that two values can be equal even if one of them is null and another is not.

Reads a variant p from the stream s.

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enum QVariant::Type▲

[explicit] QVariant::QVariant(QVariant::Type type)▲

bool QVariant::canConvert(int targetTypeId) const▲

bool QVariant::convert(int targetTypeId)▲

[static] QVariant::Type QVariant::nameToType(const char *name)▲

QVariant::Type QVariant::type() const▲

[static] const char *QVariant::typeToName(int typeId)▲