QJsonDocument Class

The QJsonDocument class provides a way to read and write JSON documents. More...

Header: #include <QJsonDocument>
CMake: find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core
Since: Qt 5.0

Note: All functions in this class are reentrant.

Public Types

enum JsonFormat { Indented, Compact }

Public Functions

QJsonDocument(const QJsonObject &object)
QJsonDocument(const QJsonArray &array)
QJsonDocument(const QJsonDocument &other)
QJsonDocument(QJsonDocument &&other)
QJsonArray array() const
bool isArray() const
bool isEmpty() const
bool isNull() const
bool isObject() const
QJsonObject object() const
void setArray(const QJsonArray &array)
void setObject(const QJsonObject &object)
void swap(QJsonDocument &other)
QByteArray toJson(QJsonDocument::JsonFormat format = Indented) const
QVariant toVariant() const
bool operator!=(const QJsonDocument &other) const
QJsonDocument &operator=(const QJsonDocument &other)
QJsonDocument &operator=(QJsonDocument &&other)
bool operator==(const QJsonDocument &other) const
const QJsonValue operator[](const QString &key) const
const QJsonValue operator[](QStringView key) const
const QJsonValue operator[](QLatin1StringView key) const
const QJsonValue operator[](qsizetype i) const

Static Public Members

const uint BinaryFormatTag
QJsonDocument fromJson(const QByteArray &json, QJsonParseError *error = nullptr)
QJsonDocument fromVariant(const QVariant &variant)
QDebug operator<<(QDebug, const QJsonDocument &)

Detailed Description

QJsonDocument is a class that wraps a complete JSON document and can read this document from, and write it to, a UTF-8 encoded text-based representation.

A JSON document can be converted from its text-based representation to a QJsonDocument using QJsonDocument::fromJson(). toJson() converts it back to text. The parser is very fast and efficient and converts the JSON to the binary representation used by Qt.

Validity of the parsed document can be queried with !isNull()

A document can be queried as to whether it contains an array or an object using isArray() and isObject(). The array or object contained in the document can be retrieved using array() or object() and then read or manipulated.

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

Member Type Documentation

[since 5.1] enum QJsonDocument::JsonFormat

This value defines the format of the JSON byte array produced when converting to a QJsonDocument using toJson().

QJsonDocument::Indented0Defines human readable output as follows:
        "Array": [
        "Key": "Value",
        "null": null
QJsonDocument::Compact1Defines a compact output as follows:

This enum was introduced or modified in Qt 5.1.

Member Function Documentation


Constructs an empty and invalid document.

QJsonDocument::QJsonDocument(const QJsonObject &object)

Creates a QJsonDocument from object.

QJsonDocument::QJsonDocument(const QJsonArray &array)

Constructs a QJsonDocument from array.

QJsonDocument::QJsonDocument(const QJsonDocument &other)

Creates a copy of the other document.

[since 5.10] QJsonDocument::QJsonDocument(QJsonDocument &&other)

Move-constructs a QJsonDocument from other.

This function was introduced in Qt 5.10.


Deletes the document.

Binary data set with fromRawData is not freed.

QJsonArray QJsonDocument::array() const

Returns the QJsonArray contained in the document.

Returns an empty array if the document contains an object.

See also isArray(), object(), and setArray().

[static] QJsonDocument QJsonDocument::fromJson(const QByteArray &json, QJsonParseError *error = nullptr)

Parses json as a UTF-8 encoded JSON document, and creates a QJsonDocument from it.

Returns a valid (non-null) QJsonDocument if the parsing succeeds. If it fails, the returned document will be null, and the optional error variable will contain further details about the error.

See also toJson(), QJsonParseError, and isNull().

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

Creates a QJsonDocument from the QVariant variant.

If the variant contains any other type than a QVariantMap, QVariantHash, QVariantList or QStringList, the returned document is invalid.

See also toVariant().

bool QJsonDocument::isArray() const

Returns true if the document contains an array.

See also array() and isObject().

bool QJsonDocument::isEmpty() const

Returns true if the document doesn't contain any data.

bool QJsonDocument::isNull() const

returns true if this document is null.

Null documents are documents created through the default constructor.

Documents created from UTF-8 encoded text or the binary format are validated during parsing. If validation fails, the returned document will also be null.

bool QJsonDocument::isObject() const

Returns true if the document contains an object.

See also object() and isArray().

QJsonObject QJsonDocument::object() const

Returns the QJsonObject contained in the document.

Returns an empty object if the document contains an array.

See also isObject(), array(), and setObject().

void QJsonDocument::setArray(const QJsonArray &array)

Sets array as the main object of this document.

See also setObject() and array().

void QJsonDocument::setObject(const QJsonObject &object)

Sets object as the main object of this document.

See also setArray() and object().

[since 5.10] void QJsonDocument::swap(QJsonDocument &other)

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

This function was introduced in Qt 5.10.

[since 5.1] QByteArray QJsonDocument::toJson(QJsonDocument::JsonFormat format = Indented) const

Converts the QJsonDocument to a UTF-8 encoded JSON document in the provided format.

This function was introduced in Qt 5.1.

See also fromJson() and JsonFormat.

QVariant QJsonDocument::toVariant() const

Returns a QVariant representing the Json document.

The returned variant will be a QVariantList if the document is a QJsonArray and a QVariantMap if the document is a QJsonObject.

See also fromVariant() and QJsonValue::toVariant().

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

returns true if other is not equal to this document

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

Assigns the other document to this QJsonDocument. Returns a reference to this object.

[since 5.10] QJsonDocument &QJsonDocument::operator=(QJsonDocument &&other)

Move-assigns other to this document.

This function was introduced in Qt 5.10.

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

Returns true if the other document is equal to this document.

[since 5.10] const QJsonValue QJsonDocument::operator[](const QString &key) const

Returns a QJsonValue representing the value for the key key.

Equivalent to calling object().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.

[since 5.14] const QJsonValue QJsonDocument::operator[](QStringView key) const

This is an overloaded function.

This function was introduced in Qt 5.14.

[since 5.10] const QJsonValue QJsonDocument::operator[](QLatin1StringView key) const

This is an overloaded function.

This function was introduced in Qt 5.10.

[since 5.10] const QJsonValue QJsonDocument::operator[](qsizetype i) const

Returns a QJsonValue representing the value for index i.

Equivalent to calling array().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.

Member Variable Documentation

const uint QJsonDocument::BinaryFormatTag

Related Non-Members

QDebug operator<<(QDebug, const QJsonDocument &)

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