QJsonDocument Class

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

• List of all members, including inherited members

Note: All functions in this class are reentrant.

Public Types

Public Functions

Static Public Members

Detailed Description

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

QJsonDocument is a class that wraps a complete JSON document and can read and write this document both from a UTF-8 encoded text based representation as well as Qt's own binary format.

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.

A document can also be created from a stored binary representation using fromBinaryData() or fromRawData().

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

Member Type Documentation

enum QJsonDocument::DataValidation

This value is used to tell QJsonDocument whether to validate the binary data when converting to a QJsonDocument using fromBinaryData() or fromRawData().

enum QJsonDocument::JsonFormat

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

    {
        "Array": [
            true,
            999,
            "string"
        ],
        "Key": "Value",
        "null": null
    }

    {"Array":[true,999,"string"],"Key":"Value","null":null}

This enum was introduced or modified in Qt 5.1.

Member Function Documentation

QJsonDocument::QJsonDocument()

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.

QJsonDocument::QJsonDocument(QJsonDocument &&other)

Move-constructs a QJsonDocument from other.

This function was introduced in Qt 5.10.

QJsonDocument::~QJsonDocument()

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::fromBinaryData(const QByteArray &data, QJsonDocument::DataValidation validation = Validate)

Creates a QJsonDocument from data.

validation decides whether the data is checked for validity before being used. By default the data is validated. If the data is not valid, the method returns a null document.

See also toBinaryData(), fromRawData(), isNull(), and DataValidation.

[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::fromRawData(const char *data, int size, QJsonDocument::DataValidation validation = Validate)

Creates a QJsonDocument that uses the first size bytes from data. It assumes data contains a binary encoded JSON document. The created document does not take ownership of data and the caller has to guarantee that data will not be deleted or modified as long as any QJsonDocument, QJsonObject or QJsonArray still references the data.

data has to be aligned to a 4 byte boundary.

validation decides whether the data is checked for validity before being used. By default the data is validated. If the data is not valid, the method returns a null document.

Returns a QJsonDocument representing the data.

See also rawData(), fromBinaryData(), isNull(), and DataValidation.

[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().

const char *QJsonDocument::rawData(int *size) const

Returns the raw binary representation of the data size will contain the size of the returned data.

This method is useful to e.g. stream the JSON document in it's binary form to a file.

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().

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.

QByteArray QJsonDocument::toBinaryData() const

Returns a binary representation of the document.

The binary representation is also the native format used internally in Qt, and is very efficient and fast to convert to and from.

The binary format can be stored on disk and interchanged with other applications or computers. fromBinaryData() can be used to convert it back into a JSON document.

See also fromBinaryData().

QByteArray QJsonDocument::toJson() const

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

See also fromJson().

QByteArray QJsonDocument::toJson(QJsonDocument::JsonFormat format) 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.

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.

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.

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

This is an overloaded function.

This function was introduced in Qt 5.10.

const QJsonValue QJsonDocument::operator[](int 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.