QJsonValue Class

The QJsonValue class encapsulates a value in JSON. More...

Header: #include <QJsonValue>
qmake: QT += core
Since: Qt 5.0

This class was introduced in Qt 5.0.

Note: All functions in this class are reentrant.

Public Types

enum Type { Null, Bool, Double, String, ..., Undefined }

Public Functions

QJsonValue(QJsonValue &&other)
QJsonValue(const QJsonValue &other)
QJsonValue(const QJsonObject &o)
QJsonValue(const QJsonArray &a)
QJsonValue(const char *s)
QJsonValue(QLatin1String s)
QJsonValue(const QString &s)
QJsonValue(qint64 n)
QJsonValue(int n)
QJsonValue(double n)
QJsonValue(bool b)
QJsonValue(QJsonValue::Type type = Null)
QJsonValue &operator=(QJsonValue &&other)
QJsonValue &operator=(const QJsonValue &other)
~QJsonValue()
bool isArray() const
bool isBool() const
bool isDouble() const
bool isNull() const
bool isObject() const
bool isString() const
bool isUndefined() const
void swap(QJsonValue &other)
QJsonArray toArray(const QJsonArray &defaultValue) const
QJsonArray toArray() const
bool toBool(bool defaultValue = false) const
double toDouble(double defaultValue = 0) const
int toInt(int defaultValue = 0) const
QJsonObject toObject(const QJsonObject &defaultValue) const
QJsonObject toObject() const
QString toString() const
QString toString(const QString &defaultValue) const
QVariant toVariant() const
QJsonValue::Type type() const
bool operator!=(const QJsonValue &other) const
bool operator==(const QJsonValue &other) const
const QJsonValue operator[](const QString &key) const
const QJsonValue operator[](QStringView key) const
const QJsonValue operator[](QLatin1String key) const
const QJsonValue operator[](int i) const

Static Public Members

QJsonValue fromVariant(const QVariant &variant)

Detailed Description

A value in JSON can be one of 6 basic types:

JSON is a format to store structured data. It has 6 basic data types:

A value can represent any of the above data types. In addition, QJsonValue has one special flag to represent undefined values. This can be queried with isUndefined().

The type of the value can be queried with type() or accessors like isBool(), isString(), and so on. Likewise, the value can be converted to the type stored in it using the toBool(), toString() and so on.

Values are strictly typed internally and contrary to QVariant will not attempt to do any implicit type conversions. This implies that converting to a type that is not stored in the value will return a default constructed return value.

QJsonValueRef

QJsonValueRef is a helper class for QJsonArray and QJsonObject. When you get an object of type QJsonValueRef, you can use it as if it were a reference to a QJsonValue. If you assign to it, the assignment will apply to the element in the QJsonArray or QJsonObject from which you got the reference.

The following methods return QJsonValueRef:

See also JSON Support in Qt and JSON Save Game Example.

Member Type Documentation

enum QJsonValue::Type

This enum describes the type of the JSON value.

ConstantValueDescription
QJsonValue::Null0x0A Null value
QJsonValue::Bool0x1A boolean value. Use toBool() to convert to a bool.
QJsonValue::Double0x2A double. Use toDouble() to convert to a double.
QJsonValue::String0x3A string. Use toString() to convert to a QString.
QJsonValue::Array0x4An array. Use toArray() to convert to a QJsonArray.
QJsonValue::Object0x5An object. Use toObject() to convert to a QJsonObject.
QJsonValue::Undefined0x80The value is undefined. This is usually returned as an error condition, when trying to read an out of bounds value in an array or a non existent key in an object.

Member Function Documentation

QJsonValue::QJsonValue(QJsonValue &&other)

Move-constructs a QJsonValue from other.

This function was introduced in Qt 5.10.

QJsonValue::QJsonValue(const QJsonValue &other)

Creates a copy of other.

QJsonValue::QJsonValue(const QJsonObject &o)

Creates a value of type Object, with value o.

QJsonValue::QJsonValue(const QJsonArray &a)

Creates a value of type Array, with value a.

QJsonValue::QJsonValue(const char *s)

Creates a value of type String with value s, assuming UTF-8 encoding of the input.

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

This function was introduced in Qt 5.3.

QJsonValue::QJsonValue(QLatin1String s)

Creates a value of type String, with value s.

QJsonValue::QJsonValue(const QString &s)

Creates a value of type String, with value s.

QJsonValue::QJsonValue(qint64 n)

This is an overloaded function.

Creates a value of type Double, with value n. NOTE: the integer limits for IEEE 754 double precision data is 2^53 (-9007199254740992 to +9007199254740992). If you pass in values outside this range expect a loss of precision to occur.

QJsonValue::QJsonValue(int n)

This is an overloaded function.

Creates a value of type Double, with value n.

QJsonValue::QJsonValue(double n)

Creates a value of type Double, with value n.

QJsonValue::QJsonValue(bool b)

Creates a value of type Bool, with value b.

QJsonValue::QJsonValue(QJsonValue::Type type = Null)

Creates a QJsonValue of type type.

The default is to create a Null value.

QJsonValue &QJsonValue::operator=(QJsonValue &&other)

Move-assigns other to this value.

This function was introduced in Qt 5.10.

QJsonValue &QJsonValue::operator=(const QJsonValue &other)

Assigns the value stored in other to this object.

QJsonValue::~QJsonValue()

Destroys the value.

[static] QJsonValue QJsonValue::fromVariant(const QVariant &variant)

Converts variant to a QJsonValue and returns it.

The conversion will convert QVariant types as follows:

For all other QVariant types a conversion to a QString will be attempted. If the returned string is empty, a Null QJsonValue will be stored, otherwise a String value using the returned QString.

See also toVariant().

bool QJsonValue::isArray() const

Returns true if the value contains an array.

See also toArray().

bool QJsonValue::isBool() const

Returns true if the value contains a boolean.

See also toBool().

bool QJsonValue::isDouble() const

Returns true if the value contains a double.

See also toDouble().

bool QJsonValue::isNull() const

Returns true if the value is null.

bool QJsonValue::isObject() const

Returns true if the value contains an object.

See also toObject().

bool QJsonValue::isString() const

Returns true if the value contains a string.

See also toString().

bool QJsonValue::isUndefined() const

Returns true if the value is undefined. This can happen in certain error cases as e.g. accessing a non existing key in a QJsonObject.

void QJsonValue::swap(QJsonValue &other)

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

This function was introduced in Qt 5.10.

QJsonArray QJsonValue::toArray(const QJsonArray &defaultValue) const

Converts the value to an array and returns it.

If type() is not Array, the defaultValue will be returned.

QJsonArray QJsonValue::toArray() const

This is an overloaded function.

Converts the value to an array and returns it.

If type() is not Array, a QJsonArray() will be returned.

bool QJsonValue::toBool(bool defaultValue = false) const

Converts the value to a bool and returns it.

If type() is not bool, the defaultValue will be returned.

double QJsonValue::toDouble(double defaultValue = 0) const

Converts the value to a double and returns it.

If type() is not Double, the defaultValue will be returned.

int QJsonValue::toInt(int defaultValue = 0) const

Converts the value to an int and returns it.

If type() is not Double or the value is not a whole number, the defaultValue will be returned.

This function was introduced in Qt 5.2.

QJsonObject QJsonValue::toObject(const QJsonObject &defaultValue) const

Converts the value to an object and returns it.

If type() is not Object, the defaultValue will be returned.

QJsonObject QJsonValue::toObject() const

This is an overloaded function.

Converts the value to an object and returns it.

If type() is not Object, the QJsonObject() will be returned.

QString QJsonValue::toString() const

Converts the value to a QString and returns it.

If type() is not String, a null QString will be returned.

See also QString::isNull().

QString QJsonValue::toString(const QString &defaultValue) const

Converts the value to a QString and returns it.

If type() is not String, the defaultValue will be returned.

QVariant QJsonValue::toVariant() const

Converts the value to a QVariant().

The QJsonValue types will be converted as follows:

ConstantDescription
NullQMetaType::Nullptr
BoolQMetaType::Bool
DoubleQMetaType::Double
StringQString
ArrayQVariantList
ObjectQVariantMap
UndefinedQVariant()

See also fromVariant().

QJsonValue::Type QJsonValue::type() const

Returns the type of the value.

See also QJsonValue::Type.

bool QJsonValue::operator!=(const QJsonValue &other) const

Returns true if the value is not equal to other.

bool QJsonValue::operator==(const QJsonValue &other) const

Returns true if the value is equal to other.

const QJsonValue QJsonValue::operator[](const QString &key) const

Returns a QJsonValue representing the value for the key key.

Equivalent to calling toObject().value(key).

The returned QJsonValue is QJsonValue::Undefined if the key does not exist, or if isObject() is false.

This function was introduced in Qt 5.10.

See also QJsonValue, QJsonValue::isUndefined(), and QJsonObject.

const QJsonValue QJsonValue::operator[](QStringView key) const

This is an overloaded function.

This function was introduced in Qt 5.14.

const QJsonValue QJsonValue::operator[](QLatin1String key) const

This is an overloaded function.

This function was introduced in Qt 5.10.

const QJsonValue QJsonValue::operator[](int i) const

Returns a QJsonValue representing the value for index i.

Equivalent to calling toArray().at(i).

The returned QJsonValue is QJsonValue::Undefined, if i is out of bounds, or if isArray() is false.

This function was introduced in Qt 5.10.

See also QJsonValue, QJsonValue::isUndefined(), and QJsonArray.

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