The QJsonValue class encapsulates a value in JSON. More...
| Header: | #include <QJsonValue> |
| qmake: | QT += core |
| Since: | Qt 5.0 |
Note: All functions in this class are reentrant.
| enum | Type { Null, Bool, Double, String, ..., Undefined } |
| QJsonValue(QJsonValue::Type type = Null) | |
| QJsonValue(bool b) | |
| QJsonValue(double n) | |
| QJsonValue(int n) | |
| QJsonValue(qint64 n) | |
| QJsonValue(const QString &s) | |
| QJsonValue(QLatin1String s) | |
| QJsonValue(const char *s) | |
| QJsonValue(const QJsonArray &a) | |
| QJsonValue(const QJsonObject &o) | |
| QJsonValue(const QJsonValue &other) | |
| QJsonValue(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 |
| QJsonValue & | operator=(const QJsonValue &other) |
| QJsonValue & | operator=(QJsonValue &&other) |
| bool | operator==(const QJsonValue &other) const |
| const QJsonValue | operator[](const QString &key) const |
| const QJsonValue | operator[](QLatin1String key) const |
| const QJsonValue | operator[](int i) const |
| QJsonValue | fromVariant(const QVariant &variant) |
The QJsonValue class encapsulates a value in JSON.
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 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.
This enum describes the type of the JSON value.
| Constant | Value | Description |
|---|---|---|
QJsonValue::Null |
0x0 |
A Null value |
QJsonValue::Bool |
0x1 |
A boolean value. Use toBool() to convert to a bool. |
QJsonValue::Double |
0x2 |
A double. Use toDouble() to convert to a double. |
QJsonValue::String |
0x3 |
A string. Use toString() to convert to a QString. |
QJsonValue::Array |
0x4 |
An array. Use toArray() to convert to a QJsonArray. |
QJsonValue::Object |
0x5 |
An object. Use toObject() to convert to a QJsonObject. |
QJsonValue::Undefined |
0x80 |
The 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. |
Creates a QJsonValue of type type.
The default is to create a Null value.
Creates a value of type Bool, with value b.
Creates a value of type Double, with value n.
This is an overloaded function.
Creates a value of type Double, with value 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.
Creates a value of type String, with value s.
Creates a value of type String, with value 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.
Creates a value of type Array, with value a.
Creates a value of type Object, with value o.
Creates a copy of other.
Move-constructs a QJsonValue from other.
This function was introduced in Qt 5.10.
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:
| Source type | Destination type |
|---|---|
| QJsonValue::Null | |
| QJsonValue::Bool | |
| QJsonValue::Double | |
| QJsonValue::String | |
| QJsonValue::Array | |
| QJsonValue::Object | |
| QJsonValue::String. The conversion will use QUrl::toString() with flag QUrl::FullyEncoded, so as to ensure maximum compatibility in parsing the URL | |
| QJsonValue::String. Since Qt 5.11, the resulting string will not include braces |
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().
Returns true if the value contains an array.
See also toArray().
Returns true if the value contains a boolean.
See also toBool().
Returns true if the value contains a double.
See also toDouble().
Returns true if the value is null.
Returns true if the value contains an object.
See also toObject().
Returns true if the value contains a string.
See also toString().
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.
Swaps the value other with this. This operation is very fast and never fails.
This function was introduced in Qt 5.10.
Converts the value to an array and returns it.
If type() is not Array, the defaultValue will be returned.
This is an overloaded function.
Converts the value to an array and returns it.
If type() is not Array, a QJsonArray() will be returned.
Converts the value to a bool and returns it.
If type() is not bool, the defaultValue will be returned.
Converts the value to a double and returns it.
If type() is not Double, the defaultValue will be returned.
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.
Converts the value to an object and returns it.
If type() is not Object, the defaultValue will be returned.
This is an overloaded function.
Converts the value to an object and returns it.
If type() is not Object, the QJsonObject() will be returned.
Converts the value to a QString and returns it.
If type() is not String, a null QString will be returned.
See also QString::isNull().
Converts the value to a QString and returns it.
If type() is not String, the defaultValue will be returned.
Converts the value to a QVariant().
The QJsonValue types will be converted as follows:
| Constant | Description |
|---|---|
Null |
QMetaType::Nullptr |
Bool |
QMetaType::Bool |
Double |
QMetaType::Double |
String |
QString |
Array |
QVariantList |
Object |
QVariantMap |
Undefined |
QVariant() |
See also fromVariant().
Returns the type of the value.
See also QJsonValue::Type.
Returns true if the value is not equal to other.
Assigns the value stored in other to this object.
Move-assigns other to this value.
This function was introduced in Qt 5.10.
Returns true if the value is equal to other.
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.
This is an overloaded function.
This function was introduced in Qt 5.10.
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.
