QJsonValue Class

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

頭：	`#include <QJsonValue>`
CMake:	`find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake:	`QT += core`

所有成員列錶，包括繼承成員
QJsonValue is part of 在 Qt 中支持 JSON and 隱式共享類 .

此類 相等可比較 .

此類 相等可比較 with QJsonValueConstRef and QJsonValueRef .

注意： 此類的所有函數可重入 .

公共類型

`(從 6.9 起)`	JsonFormat
enum	Type { Null, Bool, Double, String, Array, …, Undefined }

公共函數

	QJsonValue (QJsonValue::Type type = Null)
	QJsonValue (QLatin1StringView s )
	QJsonValue (bool b )
	QJsonValue (const QJsonArray & a )
	QJsonValue (const QJsonObject & o )
	QJsonValue (const QString & s )
	QJsonValue (const char * s )
	QJsonValue (double v )
`(從 6.3 起)`	QJsonValue (QJsonArray && a )
`(從 6.3 起)`	QJsonValue (QJsonObject && o )
	QJsonValue (int v )
	QJsonValue (qint64 v )
	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
`(從 6.0 起)` qint64	toInteger (qint64 defaultValue = 0) const
`(從 6.9 起)` QByteArray	toJson (QJsonValue::JsonFormat format = JsonFormat::Indented) const
QJsonObject	toObject (const QJsonObject & defaultValue ) const
QJsonObject	toObject () const
QString	toString () const
QString	toString (const QString & defaultValue ) const
`(從 6.10 起)` QAnyStringView	toStringView (QAnyStringView defaultValue = {}) const
QVariant	toVariant () const
QJsonValue::Type	type () const
QJsonValue &	operator= (QJsonValue && other )
QJsonValue &	operator= (const QJsonValue & other )
const QJsonValue	operator[] (const QString & key ) const
const QJsonValue	operator[] (qsizetype i ) const
const QJsonValue	operator[] (QLatin1StringView key ) const
const QJsonValue	operator[] (QStringView key ) const

靜態公共成員

`(從 6.9 起)` QJsonValue	fromJson (QByteArrayView json , QJsonParseError * error = nullptr)
QJsonValue	fromVariant (const QVariant & variant )

bool	operator!= (const QJsonValue & lhs , const QJsonValue & rhs )
bool	operator== (const QJsonValue & lhs , const QJsonValue & rhs )

詳細描述

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

JSON 是結構化數據存儲格式。它有 6 種基本數據類型：

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 :

QJsonArray ::operator[](qsizetype i)
QJsonObject ::operator[](const QString & key) const

另請參閱 在 Qt 中支持 JSON and 保存和加載遊戲 .

成員類型文檔編製

`[alias, since 6.9]` QJsonValue:: JsonFormat

如同 QJsonDocument::JsonFormat .

This typedef was introduced in Qt 6.9.

enum QJsonValue:: Type

This enum describes the type of the JSON value.

常量	值	描述
`QJsonValue::Null`	`0x0`	A Null value
`QJsonValue::Bool`	`0x1`	A boolean value. Use toBool () to convert to a bool.
`QJsonValue::Double`	`0x2`	A number value. Use toDouble () to convert to a double, or toInteger () to convert to a qint64.
`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.

成員函數文檔編製

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

Creates a QJsonValue of type type .

The default is to create a Null value.

QJsonValue:: QJsonValue ( QLatin1StringView s )

Creates a value of type String, with the Latin-1 string viewed by s .

QJsonValue:: QJsonValue ( bool b )

Creates a value of type Bool, with value b .

QJsonValue:: QJsonValue (const QJsonArray & a )

Creates a value of type Array, with value a .

QJsonValue:: QJsonValue (const QJsonObject & o )

Creates a value of type Object, with value o .

QJsonValue:: QJsonValue (const QString & s )

Creates a value of type String, with value s .

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 當編譯應用程序時。

QJsonValue:: QJsonValue ( double v )

Creates a value of type Double, with value v .

`[noexcept, since 6.3]` QJsonValue:: QJsonValue ( QJsonArray && a )

這是重載函數。

該函數在 Qt 6.3 引入。

`[noexcept, since 6.3]` QJsonValue:: QJsonValue ( QJsonObject && o )

這是重載函數。

該函數在 Qt 6.3 引入。

QJsonValue:: QJsonValue ( int v )

Creates a value of type Double, with value v .

這是重載函數。

QJsonValue:: QJsonValue ( qint64 v )

Creates a value of type Double, with value v .

This is stored internally as a 64-bit integer, so retains its full precision, as long as it is retrieved with toInteger (). However, retrieving its value with toDouble () will lose precision unless the value lies between ±2^53.

這是重載函數。

另請參閱 toInteger () 和 toDouble ().

`[noexcept]` QJsonValue:: QJsonValue (const QJsonValue & other )

創建副本為 other .

`[noexcept]` QJsonValue:: QJsonValue ( QJsonValue && other )

Move-constructs a QJsonValue from other .

`[noexcept]` QJsonValue:: ~QJsonValue ()

Destroys the value.

`[static, since 6.9]` QJsonValue QJsonValue:: fromJson ( QByteArrayView json , QJsonParseError * error = nullptr)

剖析 json as a UTF-8 encoded JSON value, and creates a QJsonValue 從它。

Returns a valid QJsonValue if the parsing succeeds. If it fails, the returned value will be undefined , and the optional error 變量將包含有關錯誤的進一步細節。

該函數在 Qt 6.9 引入。

另請參閱 QJsonParseError , isUndefined ()，和 toJson ().

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

轉換 variant 到 QJsonValue 並返迴它。

The conversion will convert QVariant types as follows:

Source type	Destination type
QMetaType::Nullptr	QJsonValue::Null
QMetaType::Bool	QJsonValue::Bool
QMetaType::Int QMetaType::UInt QMetaType::LongLong QMetaType::ULongLong QMetaType::Float QMetaType::Double	QJsonValue::Double
QMetaType::QString	QJsonValue::String
QMetaType::QStringList QMetaType::QVariantList	QJsonValue::Array
QMetaType::QVariantMap QMetaType::QVariantHash	QJsonValue::Object
QMetaType::QUrl	QJsonValue::String . The conversion will use QUrl::toString () with flag QUrl::FullyEncoded , so as to ensure maximum compatibility in parsing the URL
QMetaType::QUuid	QJsonValue::String . Since Qt 5.11, the resulting string will not include braces
QMetaType::QCborValue	Whichever type QCborValue::toJsonValue () returns.
QMetaType::QCborArray	QJsonValue::Array 。見 QCborValue::toJsonValue () for conversion restrictions.
QMetaType::QCborMap	QJsonValue::Map. See QCborValue::toJsonValue () for conversion restrictions and the "stringification" of map keys.

Loss of information and other types

QVariant can carry more information than is representable in JSON. If the QVariant is not one of the types above, the conversion is not guaranteed and is subject to change in future versions of Qt, as the UUID one did. Code should strive not to use any other types than those listed above.

若 QVariant::isNull () 返迴 true，null QJsonValue is returned or inserted into the list or object, regardless of the type carried by QVariant . Note the behavior change in Qt 6.0 affecting QVariant::isNull () also affects this function.

A floating point value that is either an infinity or NaN will be converted to a null JSON value. Since Qt 6.0, QJsonValue can store the full precision of any 64-bit signed integer without loss, but in previous versions values outside the range of ±2^53 may lose precision. Unsigned 64-bit values greater than or equal to 2^63 will either lose precision or alias to negative values, so QMetaType::ULongLong should be avoided.

For other types not listed above, a conversion to string will be attempted, usually but not always by calling QVariant::toString (). If the conversion fails the value is replaced by a null JSON value. Note that QVariant::toString () is also lossy for the majority of types. For example, if the passed QVariant is representing raw byte array data, it is recommended to pre-encode it to Base64 (or another lossless encoding), otherwise a lossy conversion using QString::fromUtf8 () 會被使用。

Please note that the conversions via QVariant::toString () are subject to change at any time. Both QVariant and QJsonValue may be extended in the future to support more types, which will result in a change in how this function performs conversions.

另請參閱 toVariant () 和 QCborValue::fromVariant ().

bool QJsonValue:: isArray () const

返迴 true if the value contains an array.

另請參閱 toArray ().

bool QJsonValue:: isBool () const

返迴 true if the value contains a boolean.

另請參閱 toBool ().

bool QJsonValue:: isDouble () const

返迴 true if the value contains a double.

另請參閱 toDouble ().

bool QJsonValue:: isNull () const

返迴 true if the value is null.

bool QJsonValue:: isObject () const

返迴 true if the value contains an object.

另請參閱 toObject ().

bool QJsonValue:: isString () const

返迴 true if the value contains a string.

另請參閱 toString ().

bool QJsonValue:: isUndefined () const

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

`[noexcept]` void QJsonValue:: swap ( QJsonValue & other )

Swaps this value with other 。此操作很快且從不失敗。

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

Converts the value to an array and returns it.

若 type () is not Array, the defaultValue 將被返迴。

QJsonArray QJsonValue:: toArray () const

Converts the value to an array and returns it.

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

這是重載函數。

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

Converts the value to a bool and returns it.

若 type () is not bool, the defaultValue 將被返迴。

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

Converts the value to a double and returns it.

若 type () is not Double, the defaultValue 將被返迴。

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

Converts the value to an int and returns it.

若 type () is not Double or the value is not a whole number, the defaultValue 將被返迴。

`[since 6.0]` qint64 QJsonValue:: toInteger ( qint64 defaultValue = 0) const

Converts the value to an integer and returns it.

若 type () is not Double or the value is not a whole number representable as qint64, the defaultValue 將被返迴。

該函數在 Qt 6.0 引入。

`[since 6.9]` QByteArray QJsonValue:: toJson ( QJsonValue::JsonFormat format = JsonFormat::Indented) const

轉換 QJsonValue to a UTF-8 encoded JSON value in the provided format .

該函數在 Qt 6.9 引入。

另請參閱 fromJson () 和 JsonFormat .

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

Converts the value to an object and returns it.

若 type () is not Object, the defaultValue 將被返迴。

QJsonObject QJsonValue:: toObject () const

Converts the value to an object and returns it.

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

這是重載函數。

QString QJsonValue:: toString () const

Converts the value to a QString 並返迴它。

若 type () is not String, a null QString 將被返迴。

另請參閱 QString::isNull ().

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

Converts the value to a QString 並返迴它。

若 type () is not String, the defaultValue 將被返迴。

另請參閱 toStringView ().

`[since 6.10]` QAnyStringView QJsonValue:: toStringView ( QAnyStringView defaultValue = {}) const

Returns the string value stored in this QJsonValue , if it is of the string type. Otherwise, it returns defaultValue 。由於 QJsonValue stores strings in either US-ASCII, UTF-8 or UTF-16, the returned QAnyStringView may be in any of these encodings.

This function does not allocate memory. The return value is valid until the next call to a non-const member function on this object. If this object goes out of scope, the return value is valid until the next call to a non-const member function on the parent JSON object or array.

該函數在 Qt 6.10 引入。

另請參閱 toString ().

QVariant QJsonValue:: toVariant () const

Converts the value to a QVariant ().

The QJsonValue types will be converted as follows:

常量	描述
`Null`	QMetaType::Nullptr
`Bool`	QMetaType::Bool
`Double`	QMetaType::Double or QMetaType::LongLong
`String`	QString
`Array`	QVariantList
`Object`	QVariantMap
`Undefined`	QVariant ()

另請參閱 fromVariant ().

QJsonValue::Type QJsonValue:: type () const

Returns the type of the value.

另請參閱 QJsonValue::Type .

`[noexcept]` QJsonValue &QJsonValue:: operator= ( QJsonValue && other )

移動賦值 other to this value.

`[noexcept]` QJsonValue &QJsonValue:: operator= (const QJsonValue & other )

Assigns the value stored in other 到此對象。

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

返迴 QJsonValue 錶示值為鍵 key .

相當於調用 toObject ().value(key).

返迴的 QJsonValue is QJsonValue::Undefined 若鍵不存在，或者若 isObject () 為 false。

另請參閱 QJsonValue , QJsonValue::isUndefined ()，和 QJsonObject .

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

返迴 QJsonValue representing the value for index i .

相當於調用 toArray ().at(i).

返迴的 QJsonValue is QJsonValue::Undefined ，若 i 超齣邊界，或者若 isArray () 為 false。

另請參閱 QJsonValue , QJsonValue::isUndefined ()，和 QJsonArray .

const QJsonValue QJsonValue:: operator[] ( QLatin1StringView key ) const

這是重載函數。

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

這是重載函數。

QJsonValue Class

公共類型

公共函數

靜態公共成員

相關非成員

詳細描述

QJsonValueRef

成員類型文檔編製

[alias, since 6.9] QJsonValue:: JsonFormat

enum QJsonValue:: Type

成員函數文檔編製

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

QJsonValue:: QJsonValue ( QLatin1StringView s )

QJsonValue:: QJsonValue ( bool b )

QJsonValue:: QJsonValue (const QJsonArray & a )

QJsonValue:: QJsonValue (const QJsonObject & o )

QJsonValue:: QJsonValue (const QString & s )

QJsonValue:: QJsonValue (const char * s )

QJsonValue:: QJsonValue ( double v )

[noexcept, since 6.3] QJsonValue:: QJsonValue ( QJsonArray && a )

[noexcept, since 6.3] QJsonValue:: QJsonValue ( QJsonObject && o )

QJsonValue:: QJsonValue ( int v )

QJsonValue:: QJsonValue ( qint64 v )

[noexcept] QJsonValue:: QJsonValue (const QJsonValue & other )

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

[noexcept] QJsonValue:: ~QJsonValue ()

[static, since 6.9] QJsonValue QJsonValue:: fromJson ( QByteArrayView json , QJsonParseError * error = nullptr)

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

Loss of information and other types

bool QJsonValue:: isArray () const

bool QJsonValue:: isBool () const

bool QJsonValue:: isDouble () const

bool QJsonValue:: isNull () const

bool QJsonValue:: isObject () const

bool QJsonValue:: isString () const

bool QJsonValue:: isUndefined () const

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

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

QJsonArray QJsonValue:: toArray () const

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

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

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

[since 6.0] qint64 QJsonValue:: toInteger ( qint64 defaultValue = 0) const

[since 6.9] QByteArray QJsonValue:: toJson ( QJsonValue::JsonFormat format = JsonFormat::Indented) const

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

QJsonObject QJsonValue:: toObject () const

QString QJsonValue:: toString () const

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

[since 6.10] QAnyStringView QJsonValue:: toStringView ( QAnyStringView defaultValue = {}) const

QVariant QJsonValue:: toVariant () const

QJsonValue::Type QJsonValue:: type () const

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

[noexcept] QJsonValue &QJsonValue:: operator= (const QJsonValue & other )

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

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

const QJsonValue QJsonValue:: operator[] ( QLatin1StringView key ) const

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

相關非成員

[noexcept] bool operator!= (const QJsonValue & lhs , const QJsonValue & rhs )

[noexcept] bool operator== (const QJsonValue & lhs , const QJsonValue & rhs )

內容

`[alias, since 6.9]` QJsonValue:: JsonFormat

`[noexcept, since 6.3]` QJsonValue:: QJsonValue ( QJsonArray && a )

`[noexcept, since 6.3]` QJsonValue:: QJsonValue ( QJsonObject && o )

`[noexcept]` QJsonValue:: QJsonValue (const QJsonValue & other )

`[noexcept]` QJsonValue:: QJsonValue ( QJsonValue && other )

`[noexcept]` QJsonValue:: ~QJsonValue ()

`[static, since 6.9]` QJsonValue QJsonValue:: fromJson ( QByteArrayView json , QJsonParseError * error = nullptr)

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

`[noexcept]` void QJsonValue:: swap ( QJsonValue & other )

`[since 6.0]` qint64 QJsonValue:: toInteger ( qint64 defaultValue = 0) const

`[since 6.9]` QByteArray QJsonValue:: toJson ( QJsonValue::JsonFormat format = JsonFormat::Indented) const

`[since 6.10]` QAnyStringView QJsonValue:: toStringView ( QAnyStringView defaultValue = {}) const

`[noexcept]` QJsonValue &QJsonValue:: operator= ( QJsonValue && other )

`[noexcept]` QJsonValue &QJsonValue:: operator= (const QJsonValue & other )

`[noexcept]` bool operator!= (const QJsonValue & lhs , const QJsonValue & rhs )

`[noexcept]` bool operator== (const QJsonValue & lhs , const QJsonValue & rhs )