QVariant Class

Member Function Documentation

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

See also metaType().

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

See also get_if() and QMetaType.

[noexcept] QVariant::QVariant()

Constructs an invalid variant.

[noexcept] QVariant::QVariant(QChar c)

Constructs a new variant with a char value, c.

QVariant::QVariant(const char *val)

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.

[noexcept] QVariant::QVariant(double val)

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

[noexcept] QVariant::QVariant(float val)

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

[noexcept] QVariant::QVariant(int val)

Constructs a new variant with an integer value, val.

[noexcept] QVariant::QVariant(qlonglong val)

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

[noexcept] QVariant::QVariant(qulonglong val)

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

[noexcept] QVariant::QVariant(uint val)

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

[explicit] QVariant::QVariant(QMetaType type, const void *copy = nullptr)

Constructs a variant of type type, and initializes it with a copy of *copy if copy is not nullptr (in which case, copy must point to an object of type type).

Note that you have to pass the address of the object 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 construction and copy is not nullptr, the variant will be invalid. Similarly, if copy is nullptr and type does not support default construction, the variant will be invalid.

See also QVariant::fromMetaType, QVariant::fromValue(), and QMetaType::Type.

[explicit noexcept(...), since 6.6] template <typename T, typename... Args, QVariant::if_constructible<T, Args...> = true> QVariant::QVariant(std::in_place_type_t<T>, Args &&... args)

Constructs a new variant containing a value of type T. The contained value is is initialized with the arguments std::forward<Args>(args)....

This overload only participates in overload resolution if T can be constructed from args.

This constructor is provided for STL/std::any compatibility.

This is an overloaded function.

This function was introduced in Qt 6.6.

[explicit noexcept(...), since 6.6] template <typename T, typename U, typename... Args, QVariant::if_constructible<T, std::initializer_list<U> &, Args...> = true> QVariant::QVariant(std::in_place_type_t<T>, std::initializer_list<U> il, Args &&... args)

This is an overloaded function.

This overload exists to support types with constructors taking an initializer_list. It behaves otherwise equivalent to the non-initializer list in_place_type_t overload.

This function was introduced in Qt 6.6.

[noexcept] QVariant::QVariant(QDate val)

Constructs a new variant with a date value, val.

QVariant::QVariant(QLatin1StringView val)

Constructs a new variant with a QString value from the Latin-1 string viewed by val.

[noexcept(...)] QVariant::QVariant(QLine val)

Constructs a new variant with a line value of val.

[noexcept(...)] QVariant::QVariant(QLineF val)

Constructs a new variant with a line value of val.

[noexcept] QVariant::QVariant(QPoint val)

Constructs a new variant with a point value of val.

[noexcept(...)] QVariant::QVariant(QPointF val)

Constructs a new variant with a point value of val.

[noexcept(...)] QVariant::QVariant(QRect val)

Constructs a new variant with a rect value of val.

[noexcept(...)] QVariant::QVariant(QRectF val)

Constructs a new variant with a rect value of val.

[noexcept] QVariant::QVariant(QSize val)

Constructs a new variant with a size value of val.

[noexcept(...)] QVariant::QVariant(QSizeF val)

Constructs a new variant with a size value of val.

[noexcept] QVariant::QVariant(QTime val)

Constructs a new variant with a time value, val.

[noexcept(...)] QVariant::QVariant(QUuid val)

Constructs a new variant with an uuid value, val.

[noexcept] QVariant::QVariant(bool val)

Constructs a new variant with a boolean value, val.

[noexcept] QVariant::QVariant(const QBitArray &val)

Constructs a new variant with a bitarray value, val.

[noexcept] QVariant::QVariant(const QByteArray &val)

Constructs a new variant with a bytearray value, val.

[noexcept] QVariant::QVariant(const QDateTime &val)

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

QVariant::QVariant(const QEasingCurve &val)

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

[noexcept] QVariant::QVariant(const QHash<QString, QVariant> &val)

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

[noexcept] QVariant::QVariant(const QJsonArray &val)

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

QVariant::QVariant(const QJsonDocument &val)

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

[noexcept] QVariant::QVariant(const QJsonObject &val)

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

[noexcept(...)] QVariant::QVariant(const QJsonValue &val)

Constructs a new variant with a json value, val.

[noexcept] QVariant::QVariant(const QList<QVariant> &val)

Constructs a new variant with a list value, val.

[noexcept] QVariant::QVariant(const QLocale &l)

Constructs a new variant with a locale value, l.

[noexcept] QVariant::QVariant(const QMap<QString, QVariant> &val)

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

[noexcept(...)] QVariant::QVariant(const QModelIndex &val)

Constructs a new variant with a QModelIndex value, val.

QVariant::QVariant(const QPersistentModelIndex &val)

Constructs a new variant with a QPersistentModelIndex value, val.

[noexcept] QVariant::QVariant(const QRegularExpression &re)

Constructs a new variant with the regular expression value re.

[noexcept] QVariant::QVariant(const QString &val)

Constructs a new variant with a string value, val.

[noexcept] QVariant::QVariant(const QStringList &val)

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

[noexcept] QVariant::QVariant(const QUrl &val)

Constructs a new variant with a url value of val.

QVariant::QVariant(const QVariant &p)

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

[noexcept] QVariant::QVariant(QVariant &&other)

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

[noexcept] QVariant::~QVariant()

Destroys the QVariant and the contained object.

template <typename T> bool QVariant::canConvert() const

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.

See also convert().

[since 6.0] bool QVariant::canConvert(QMetaType type) const

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.

See also QMetaType::canConvert().

template <typename T> bool QVariant::canView() const

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

See also value().

void QVariant::clear()

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

[static, since 6.0] QPartialOrdering QVariant::compare(const QVariant &lhs, const QVariant &rhs)

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.

See also QMetaType::compare() and QMetaType::isOrdered().

[since 6.0] bool QVariant::convert(QMetaType targetType)

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.

See also canConvert() and clear().

void *QVariant::data()

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.

See also get_if() and QMetaType.

[since 6.6] template <typename T, typename... Args, QVariant::if_constructible<T, Args...> = true> T &QVariant::emplace(Args &&... args)

Replaces the object currently held in *this with an object of type T, constructed from args.... If *this was non-null, the previously held object is destroyed first. If possible, this method will reuse memory allocated by the QVariant. Returns a reference to the newly-created object.

This function was introduced in Qt 6.6.

[since 6.6] template <typename T, typename U, typename... Args, QVariant::if_constructible<T, std::initializer_list<U> &, Args...> = true> T &QVariant::emplace(std::initializer_list<U> list, Args &&... args)

This is an overloaded function.

This overload exists to support types with constructors taking an initializer_list. It behaves otherwise equivalent to the non-initializer list overload.

This function was introduced in Qt 6.6.

[static, since 6.7] QVariant QVariant::fromMetaType(QMetaType type, const void *copy = nullptr)

Creates a variant of type type, and initializes it with a copy of *copy if copy is not nullptr (in which case, copy must point to an object of type type).

Note that you have to pass the address of the object 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 construction and copy is not nullptr, the variant will be invalid. Similarly, if copy is nullptr and type does not support default construction, the variant will be invalid.

Returns the QVariant created as described above.

This function was introduced in Qt 6.7.

See also QVariant::fromValue() and QMetaType::Type.

[static] template <typename... Types> QVariant QVariant::fromStdVariant(const std::variant<Types...> &value)

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.

See also fromValue().

[static, since 6.6] template <typename... Types> QVariant QVariant::fromStdVariant(std::variant<Types...> &&value)

This is an overloaded function.

This function was introduced in Qt 6.6.

[static] template <typename T> QVariant QVariant::fromValue(const T &value)

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

Example:

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

See also setValue() and value().

[static, since 6.6] template <typename T, QVariant::if_rvalue<T> = true> QVariant QVariant::fromValue(T &&value)

This is an overloaded function.

This function was introduced in Qt 6.6.

bool QVariant::isNull() const

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.

See also convert().

bool QVariant::isValid() const

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

[since 6.0] QMetaType QVariant::metaType() const

Returns the QMetaType of the value stored in the variant.

This function was introduced in Qt 6.0.

void QVariant::setValue(QVariant &&value)

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

See also value().

template <typename T, typename = std::enable_if_t<!std::is_same_v<std::decay_t<T>, QVariant>>> void QVariant::setValue(T &&value)

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>();

See also value(), fromValue(), and canConvert().

void QVariant::setValue(const QVariant &value)

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

[noexcept] void QVariant::swap(QVariant &other)

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

QBitArray QVariant::toBitArray() const

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

See also canConvert() and convert().

bool QVariant::toBool() const

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.

See also canConvert() and convert().

QByteArray QVariant::toByteArray() const

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.

See also canConvert() and convert().

QChar QVariant::toChar() const

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

See also canConvert() and convert().

QDate QVariant::toDate() const

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.

See also canConvert() and convert().

QDateTime QVariant::toDateTime() const

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.

See also canConvert() and convert().

double QVariant::toDouble(bool *ok = nullptr) const

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.

See also canConvert() and convert().

QEasingCurve QVariant::toEasingCurve() const

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

See also canConvert() and convert().

float QVariant::toFloat(bool *ok = nullptr) const

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.

See also canConvert() and convert().

QHash<QString, QVariant> QVariant::toHash() const

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

See also canConvert() and convert().

int QVariant::toInt(bool *ok = nullptr) const

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().

See also canConvert() and convert().

QJsonArray QVariant::toJsonArray() const

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

See also canConvert() and convert().

QJsonDocument QVariant::toJsonDocument() const

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

See also canConvert() and convert().

QJsonObject QVariant::toJsonObject() const

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

See also canConvert() and convert().

QJsonValue QVariant::toJsonValue() const

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

See also canConvert() and convert().

QLine QVariant::toLine() const

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

See also canConvert() and convert().

QLineF QVariant::toLineF() const

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

See also canConvert() and convert().

QList<QVariant> QVariant::toList() const

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.

See also canConvert() and convert().

QLocale QVariant::toLocale() const

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

See also canConvert() and convert().

qlonglong QVariant::toLongLong(bool *ok = nullptr) const

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.

See also canConvert() and convert().

QMap<QString, QVariant> QVariant::toMap() const

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.

See also canConvert() and convert().

QModelIndex QVariant::toModelIndex() const

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

See also canConvert(), convert(), and toPersistentModelIndex().

QPersistentModelIndex QVariant::toPersistentModelIndex() const

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

See also canConvert(), convert(), and toModelIndex().

QPoint QVariant::toPoint() const

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

See also canConvert() and convert().

QPointF QVariant::toPointF() const

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

See also canConvert() and convert().

qreal QVariant::toReal(bool *ok = nullptr) const

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.

See also canConvert() and convert().

QRect QVariant::toRect() const

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

See also canConvert() and convert().

QRectF QVariant::toRectF() const

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

See also canConvert() and convert().

QRegularExpression QVariant::toRegularExpression() const

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

See also canConvert() and convert().

QSize QVariant::toSize() const

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

See also canConvert() and convert().

QSizeF QVariant::toSizeF() const

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

See also canConvert() and convert().

QString QVariant::toString() const

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.

See also canConvert() and convert().

QStringList QVariant::toStringList() const

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.

See also canConvert() and convert().

QTime QVariant::toTime() const

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.

See also canConvert() and convert().

uint QVariant::toUInt(bool *ok = nullptr) const

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().

See also canConvert() and convert().

qulonglong QVariant::toULongLong(bool *ok = nullptr) const

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.

See also canConvert() and convert().

QUrl QVariant::toUrl() const

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

See also canConvert() and convert().

QUuid QVariant::toUuid() const

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

See also canConvert() and convert().

const char *QVariant::typeName() const

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.

template <typename T> T QVariant::value() const &

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;
    }
}

See also setValue(), fromValue(), canConvert(), and Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE().

template <typename T> T QVariant::view()

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.

See also canView() and Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE().

[noexcept] QVariant &QVariant::operator=(QVariant &&other)

Move-assigns other to this QVariant instance.

QVariant &QVariant::operator=(const QVariant &variant)

Assigns the value of the variant variant to this variant.