- Qt 5.15
- Qt Core
- C++ Classes
- QJsonDocument
- Qt 5.15.19 Reference Documentation

# QJsonDocument Class

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

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

This class was introduced in Qt 5.0.

- List of all members, including inherited members
- Obsolete members

Note: All functions in this class are reentrant.

## Public Types

enum | DataValidation { Validate, BypassValidation }
enum | JsonFormat { Indented, Compact }

## Public Functions

| QJsonDocument(QJsonDocument &&other)
| QJsonDocument(const QJsonDocument &other)
| QJsonDocument(const QJsonArray &array)
| QJsonDocument(const QJsonObject &object)
| QJsonDocument()
QJsonDocument & | operator=(QJsonDocument &&other)
QJsonDocument & | operator=(const QJsonDocument &other)
| ~QJsonDocument()
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() const
QByteArray | toJson(JsonFormat format) const
QVariant | toVariant() const
bool | operator!=(const QJsonDocument &other) const
bool | operator==(const QJsonDocument &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

QJsonDocument | fromJson(const QByteArray &json, QJsonParseError *error = nullptr)
QJsonDocument | fromVariant(const QVariant &variant)

## Detailed Description

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().

Constant | Value | Description
--- | --- | ---
`QJsonDocument::Validate` | `0` | Validate the data before using it. This is the default.
`QJsonDocument::BypassValidation` | `1` | Bypasses data validation. Only use if you received the data from a trusted place and know it's valid, as using of invalid data can crash the application.

### enum QJsonDocument::JsonFormat

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

Constant | Value | Description
--- | --- | ---

`QJsonDocument::Indented`

`0`

Defines human readable output as follows:

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

`QJsonDocument::Compact`

`1`

Defines a compact output as follows:

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

This enum was introduced or modified in Qt 5.1.

## Member Function Documentation

### QJsonDocument::QJsonDocument(QJsonDocument &&other)

Move-constructs a QJsonDocument from other.

This function was introduced in Qt 5.10.

### QJsonDocument::QJsonDocument(const QJsonDocument &other)

Creates a copy of the other document.

### QJsonDocument::QJsonDocument(const QJsonArray &array)

Constructs a QJsonDocument from array.

### QJsonDocument::QJsonDocument(const QJsonObject &object)

Creates a QJsonDocument from object.

### QJsonDocument::QJsonDocument()

Constructs an empty and invalid document.

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

Move-assigns other to this document.

This function was introduced in Qt 5.10.

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

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

### 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::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().

### 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::toJson() const

Converts the QJsonDocument to an indented, UTF-8 encoded JSON document.

See also fromJson().

### QByteArray QJsonDocument::toJson(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

### 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[](QStringView key) const

This is an overloaded function.

This function was introduced in Qt 5.14.

### 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.