- Qt 6.8
- Qt Core
- C++ Classes
- QCborValue
- Qt 6.8.3 Reference Documentation

# QCborValue Class

The QCborValue class encapsulates a value in CBOR. More...

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

- List of all members, including inherited members
- QCborValue is part of CBOR Support in Qt.

This class is strongly comparable.

Note: All functions in this class are reentrant.

## Public Types

enum | DiagnosticNotationOption { Compact, LineWrapped, ExtendedFormat }
flags | DiagnosticNotationOptions
enum | EncodingOption { NoTransformation, UseFloat, UseFloat16, UseIntegers }
flags | EncodingOptions
enum | Type { Integer, ByteArray, String, Array, Map, …, Uuid }

## Public Functions

| QCborValue()
| QCborValue(QCborArray &&a)
| QCborValue(QCborMap &&m)
| QCborValue(QCborSimpleType st)
| QCborValue(QCborValue::Type t_)
| QCborValue(QStringView s)
| QCborValue(bool b)
| QCborValue(const QByteArray &ba)
| QCborValue(const QCborArray &a)
| QCborValue(const QCborMap &m)
| QCborValue(const QDateTime &dt)
| QCborValue(const QRegularExpression &rx)
| QCborValue(const QString &s)
| QCborValue(const QUrl &url)
| QCborValue(const QUuid &uuid)
| QCborValue(double d)
| QCborValue(qint64 i)
| QCborValue(QCborTag tag, const QCborValue &tv = QCborValue())
| QCborValue(QLatin1StringView s)
| QCborValue(QCborKnownTags tag, const QCborValue &tv = QCborValue())
| QCborValue(const QCborValue &other)
| QCborValue(QCborValue &&other)
| ~QCborValue()
int | compare(const QCborValue &other) const
bool | isArray() const
bool | isBool() const
bool | isByteArray() const
bool | isContainer() const
bool | isDateTime() const
bool | isDouble() const
bool | isFalse() const
bool | isInteger() const
bool | isInvalid() const
bool | isMap() const
bool | isNull() const
bool | isRegularExpression() const
bool | isSimpleType() const
bool | isSimpleType(QCborSimpleType st) const
bool | isString() const
bool | isTag() const
bool | isTrue() const
bool | isUndefined() const
bool | isUrl() const
bool | isUuid() const
void | swap(QCborValue &other)
QCborTag | tag(QCborTag defaultValue = QCborTag(-1)) const
QCborValue | taggedValue(const QCborValue &defaultValue = QCborValue()) const
QCborArray | toArray() const
QCborArray | toArray(const QCborArray &defaultValue) const
bool | toBool(bool defaultValue = false) const
QByteArray | toByteArray(const QByteArray &defaultValue = {}) const
QByteArray | toCbor(QCborValue::EncodingOptions opt = NoTransformation) const
void | toCbor(QCborStreamWriter &writer, QCborValue::EncodingOptions opt = NoTransformation) const
QDateTime | toDateTime(const QDateTime &defaultValue = {}) const
QString | toDiagnosticNotation(QCborValue::DiagnosticNotationOptions opts = Compact) const
double | toDouble(double defaultValue = 0) const
qint64 | toInteger(qint64 defaultValue = 0) const
QJsonValue | toJsonValue() const
QCborMap | toMap() const
QCborMap | toMap(const QCborMap &defaultValue) const
QRegularExpression | toRegularExpression(const QRegularExpression &defaultValue = {}) const
QCborSimpleType | toSimpleType(QCborSimpleType defaultValue = QCborSimpleType::Undefined) const
QString | toString(const QString &defaultValue = {}) const
QUrl | toUrl(const QUrl &defaultValue = {}) const
QUuid | toUuid(const QUuid &defaultValue = {}) const
QVariant | toVariant() const
QCborValue::Type | type() const
QCborValue & | operator=(const QCborValue &other)
QCborValue & | operator=(QCborValue &&other)
QCborValueRef | operator[](const QString &key)
const QCborValue | operator[](const QString &key) const
QCborValueRef | operator[](QLatin1StringView key)
QCborValueRef | operator[](qint64 key)
const QCborValue | operator[](QLatin1StringView key) const
const QCborValue | operator[](qint64 key) const

## Static Public Members

QCborValue | fromCbor(QCborStreamReader &reader)
QCborValue | fromCbor(const QByteArray &ba, QCborParserError *error = nullptr)
QCborValue | fromCbor(const char *data, qsizetype len, QCborParserError *error = nullptr)
QCborValue | fromCbor(const quint8 *data, qsizetype len, QCborParserError *error = nullptr)
QCborValue | fromJsonValue(const QJsonValue &v)
QCborValue | fromVariant(const QVariant &variant)

## Related Non-Members

bool | operator!=(const QCborValue &lhs, const QCborValue &rhs)
bool | operator<(const QCborValue &lhs, const QCborValue &rhs)
bool | operator<=(const QCborValue &lhs, const QCborValue &rhs)
bool | operator==(const QCborValue &lhs, const QCborValue &rhs)
bool | operator>(const QCborValue &lhs, const QCborValue &rhs)
bool | operator>=(const QCborValue &lhs, const QCborValue &rhs)

## Detailed Description

This class can be used to hold one of the many types available in CBOR. CBOR is the Concise Binary Object Representation, a very compact form of binary data encoding that is a superset of JSON. It was created by the IETF Constrained RESTful Environments (CoRE) WG, which has used it in many new RFCs. It is meant to be used alongside the CoAP protocol.

CBOR has three groups of built-in types:

- Basic types: integers, floating point (double), boolean, null, etc.
- String-like types: strings and byte arrays
- Containers: arrays and maps

Additionally, CBOR supports a form of type extensibility by associating a "tag" to one of the above types to convey more information. For example, a UUID is represented by a tag and a byte array containing the 16 bytes of the UUID content. QCborValue supports creating and decoding several of those extended types directly with Qt classes (like QUuid).

For the complete list, see QCborValue::Type. The type of a QCborValue can be queried using type() or one of the "isXxxx" functions.

### Extended types and tagged values

A tagged value is a normal QCborValue that is paired with a number that is its tag. See QCborKnownTags for more information on what tags are in the API as well as the full, official list. Such combinations form extended types.

QCborValue has support for certain extended types in the API, like URL (with QUrl) and UUID (with QUuid). Other extended types not supported in the API are represented by a QCborValue of Tag type. The tag can later be retrieved by tag() and the tagged value using taggedValue().

In order to support future compatibility, QCborValues containing extended Qt types compare equal to the tag type of the same contents. In other words, the following expression is true:

         QCborValue(uuid) == QCborValue(QCborKnownTags::Uuid, uuid.toRfc4122());

### Undefined and null values

QCborValue can contain a value of "null", which is not of any specific type. It resembles the C++ `std::nullptr_t` type, whose only possible value is `nullptr`. QCborValue has a constructor taking such a type and creates a null QCborValue.

Null values are used to indicate that an optional value is not present. In that aspect, it is similar to the C++ Standard Library type `std::optional` when that is disengaged. Unlike the C++ type, CBOR nulls are simply of type "Null" and it is not possible to determine what concrete type it is replacing.

QCborValue can also be of the undefined type, which represents a value of "undefined". In fact, that is what the QCborValue default constructor creates.

Undefined values are different from null values. While nulls are used to indicate an optional value that is not provided, Undefined is usually used to indicate that an expected value could not be provided, usually due to an error or a precondition that could not be satisfied.

Such values are completely valid and may appear in CBOR streams, unlike JSON content and QJsonValue's undefined bit. But like QJsonValue's Undefined, it is returned by a CBOR container's value() or read-only operator[] for invalid look-ups (index out of range for QCborArray, or key not found for QCborMap). It is not possible to tell such a case apart from the value of Undefined, so if that is required, check the QCborArray size and use the QCborMap iterator API.

### Simple types

CBOR supports additional simple types that, like Null and Undefined, carry no other value. They are called interchangeably "Simple Types" and "Simple Values". CBOR encodes booleans as two distinct types (one for `true` and one for `false`), but QCborValue has a convenience API for them.

There are currently no other defined CBOR simple types. QCborValue supports them simply by their number with API like isSimpleType() and toSimpleType(), available for compatibility with future specifications before the Qt API can be updated. Their use before such a specification is discouraged, as other CBOR implementations may not support them fully.

### CBOR support

QCborValue supports all CBOR features required to create canonical and strict streams. It implements almost all of the features specified in RFC 7049.

The following table lists the CBOR features that QCborValue supports.

Feature | Support
--- | ---
Unsigned numbers | Yes (qint64 range)
Negative numbers | Yes (qint64 range)
Byte strings | Yes
Text strings | Yes
Chunked strings | See below
Tags | Yes (arbitrary)
Booleans | Yes
Null | Yes
Undefined | Yes
Arbitrary simple values | Yes
Half-precision float (16-bit) | Yes
Single-precision float (32-bit) | Yes
Double-precision float (64-bit) | Yes
Infinities and NaN floating point | Yes
Determinate-length arrays and maps | Yes
Indeterminate-length arrays and maps | Yes
Map key types other than strings and integers | Yes (arbitrary)

Integers in QCborValue are limited to the range of the qint64 type. That is, from -9,223,372,036,854,775,808 (-263) to 9,223,372,036,854,775,807 (263 - 1). CBOR itself can represent integer values outside of this range, which QCborValue does not support. When decoding a stream using fromCbor() containing one of those values, QCborValue will convert automatically to Double, but that may lose up to 11 bits of precision.

fromCbor() is able to decode chunked strings, but will always merge the chunks together into a single QCborValue. For that reason, it always writes non-chunked strings when using toCbor() (which is required by the Canonical format anyway).

QCborValue will always convert half- and single-precision floating point values in the CBOR stream to double-precision. The toCbor() function can take a parameter indicating to recreate them.

### QCborValueRef

QCborValueRef is a helper class for QCborArray and QCborMap. It is the type you get when using one of the mutating APIs in those classes. Unlike QCborValue, new values can be assigned to that class. When that is done, the array or map it refers to will be modified with the new value. In all other aspects, its API is identical to QCborValue.

{Parsing and displaying CBOR data}

See also QCborArray, QCborMap, QCborStreamReader, QCborStreamWriter, QJsonValue, QJsonDocument, Serialization Converter, and Saving and Loading a Game.

## Member Type Documentation

### enum QCborValue::DiagnosticNotationOption
flags QCborValue::DiagnosticNotationOptions

This enum is used in the option argument to toDiagnosticNotation(), to modify the output format.

Constant | Value | Description
--- | --- | ---
`QCborValue::Compact` | `0x00` | Does not use any line-breaks, producing a compact representation.
`QCborValue::LineWrapped` | `0x01` | Uses line-breaks, one QCborValue per line.
`QCborValue::ExtendedFormat` | `0x02` | Uses some different options to represent values, not found in RFC 7049. Those options are subject to change.

Currently, `ExtendedFormat` will change how byte arrays are represented. Without it, they are always hex-encoded and without spaces. With it, QCborValue::toCbor() will either use hex with spaces, base64 or base64url encoding, depending on the context.

The DiagnosticNotationOptions type is a typedef for QFlags<DiagnosticNotationOption>. It stores an OR combination of DiagnosticNotationOption values.

See also toDiagnosticNotation().

### enum QCborValue::EncodingOption
flags QCborValue::EncodingOptions

This enum is used in the options argument to toCbor(), modifying the behavior of the encoder.

Constant | Value | Description
--- | --- | ---
`QCborValue::NoTransformation` | `0` | (Default) Performs no transformations.
`QCborValue::UseFloat` | `0x02` | Tells the encoder to use IEEE 754 single-precision floating point (that is, `float`) whenever possible.
`QCborValue::UseFloat16` | `UseFloat | 0x04` | Tells the encoder to use IEEE 754 half-precision floating point (that is, `qfloat16`), whenever possible. Implies `UseFloat`.
`QCborValue::UseIntegers` | `0x08` | Tells the encoder to use integers whenever a value of type Double contains an integer.

The use of `UseFloat16` is required to encode the stream in Canonical Format, but is not otherwise necessary.

The EncodingOptions type is a typedef for QFlags<EncodingOption>. It stores an OR combination of EncodingOption values.

See also toCbor().

### enum QCborValue::Type

This enum represents the QCborValue type. It is returned by the type() function.

The CBOR built-in types are:

Constant | Value | Description
--- | --- | ---
`QCborValue::Integer` | `0x00` | `qint64`: An integer value
`QCborValue::ByteArray` | `0x40` | QByteArray: a byte array ("byte string")
`QCborValue::String` | `0x60` | QString: a Unicode string ("text string")
`QCborValue::Array` | `0x80` | QCborArray: an array of QCborValues
`QCborValue::Map` | `0xa0` | QCborMap: an associative container of QCborValues
`QCborValue::SimpleType` | `0x100` | QCborSimpleType: one of several simple types/values
`QCborValue::False` | `SimpleType + int(QCborSimpleType::False)` | `bool`: the simple type for value `false`
`QCborValue::True` | `SimpleType + int(QCborSimpleType::True)` | `bool`: the simple type for value `true`
`QCborValue::Null` | `SimpleType + int(QCborSimpleType::Null)` | `std::nullptr_t`: the simple type for the null value
`QCborValue::Undefined` | `SimpleType + int(QCborSimpleType::Undefined)` | (no type) the simple type for the undefined value
`QCborValue::Double` | `0x202` | `double`: a double-precision floating point
`QCborValue::Invalid` | `-1` | Not a valid value, this usually indicates a CBOR decoding error

Additionally, QCborValue can represent extended types:

Constant | Value | Description
--- | --- | ---
`QCborValue::Tag` | `0xc0` | An unknown or unrecognized extended type, represented by its tag (a QCborTag) and the tagged value (a QCborValue)
`QCborValue::DateTime` | `0x10000` | QDateTime: a date and time stamp
`QCborValue::Url` | `0x10020` | QUrl: a URL or URI
`QCborValue::RegularExpression` | `0x10023` | QRegularExpression: the pattern of a regular expression
`QCborValue::Uuid` | `0x10025` | QUuid: a UUID

See also type().

## Member Function Documentation

### QCborValue::QCborValue(QCborArray &&a)

### QCborValue::QCborValue(const QCborArray &a)

Creates a QCborValue with the array a. The array can later be retrieved using toArray().

See also toArray(), isArray(), and isMap().

### QCborValue::QCborValue(QCborMap &&m)

### QCborValue::QCborValue(const QCborMap &m)

Creates a QCborValue with the map m. The map can later be retrieved using toMap().

See also toMap(), isMap(), and isArray().

### QCborValue::QCborValue(QCborKnownTags tag, const QCborValue &tv = QCborValue())

### QCborValue::QCborValue(QCborTag tag, const QCborValue &tv = QCborValue())

Creates a QCborValue for the extended type represented by the tag value tag, tagging value tv. The tag can later be retrieved using tag() and the tagged value using taggedValue().

See also isTag(), tag(), taggedValue(), and QCborKnownTags.

### QCborArray QCborValue::toArray() const

### QCborArray QCborValue::toArray(const QCborArray &defaultValue) const

Returns the array value stored in this QCborValue, if it is of the array type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QCborArray.

See also isArray(), isByteArray(), isMap(), isContainer(), and toMap().

### QCborMap QCborValue::toMap() const

### QCborMap QCborValue::toMap(const QCborMap &defaultValue) const

Returns the map value stored in this QCborValue, if it is of the map type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QCborMap.

See also isMap(), isArray(), isContainer(), and toArray().

### `[static]` QCborValue QCborValue::fromCbor(const char *data, qsizetype len, QCborParserError *error = nullptr)

### `[static]` QCborValue QCborValue::fromCbor(const quint8 *data, qsizetype len, QCborParserError *error = nullptr)

This is an overloaded function.

Converts len bytes of data to a QByteArray and then calls the overload of this function that accepts a QByteArray, also passing error, if provided.

### QCborValue::QCborValue()

Creates a QCborValue of the Undefined type.

CBOR undefined values are used to indicate missing information, usually as a result of a previous operation that did not complete as expected. They are also used by the QCborArray and QCborMap API to indicate the searched item was not found.

Undefined values are represented by the Undefined simple type. Because of that, QCborValues with undefined values will also return true for isSimpleType() and `isSimpleType(QCborSimpleType::Undefined)`.

Undefined values are different from null values.

QCborValue objects with undefined values are also different from invalid QCborValue objects. The API will not create invalid QCborValues, but they may exist as a result of a parsing error.

See also isUndefined(), isNull(), and isSimpleType().

### QCborValue::QCborValue(QCborSimpleType st)

Creates a QCborValue of simple type st. The type can later be retrieved using toSimpleType() as well as isSimpleType(st).

CBOR simple types are types that do not have any associated value, like C++'s `std::nullptr_t` type, whose only possible value is `nullptr`.

If st is `QCborSimpleType::Null`, the resulting QCborValue will be of the Null type and similarly for `QCborSimpleType::Undefined`. If st is `QCborSimpleType::False` or `QCborSimpleType::True`, the created QCborValue will be a boolean containing a value of false or true, respectively.

This function can be used with simple types not defined in the API. For example, to create a QCborValue with simple type 12, one could write:

         QCborValue value(QCborSimpleType(12));

Simple types should not be used until a specification for them has been published, since other implementations may not support them properly. Simple type values 24 to 31 are reserved and must not be used.

isSimpleType(), isNull(), isUndefined(), isTrue(), isFalse()

### QCborValue::QCborValue(QCborValue::Type t_)

Creates a QCborValue of type t_. The value associated with such a type (if any) will be default constructed.

See also type().

### QCborValue::QCborValue(QStringView s)

Creates a QCborValue with string value s. The value can later be retrieved using toString().

See also toString(), isString(), and isByteArray().

### QCborValue::QCborValue(bool b)

Creates a QCborValue with boolean value b. The value can later be retrieved using toBool().

Internally, CBOR booleans are represented by a pair of types, one for true and one for false. For that reason, boolean QCborValues will return true for isSimpleType() and one of `isSimpleType(QCborSimpleType::False)` or `isSimpleType(QCborSimpleType::True)`.

See also toBool(), isBool(), isTrue(), isFalse(), and isSimpleType().

### QCborValue::QCborValue(const QByteArray &ba)

Creates a QCborValue with byte array value ba. The value can later be retrieved using toByteArray().

See also toByteArray(), isByteArray(), and isString().

### `[explicit]` QCborValue::QCborValue(const QDateTime &dt)

Creates a QCborValue object of the date/time extended type and containing the value represented by dt. The value can later be retrieved using toDateTime().

The CBOR date/time types are extension types using tags: either a string (in ISO date format) tagged as a DateTime or a number (of seconds since the start of 1970, UTC) tagged as a UnixTime_t. When parsing CBOR streams, QCborValue will convert UnixTime_t to the string-based type.

See also toDateTime(), isDateTime(), and taggedValue().

### `[explicit]` QCborValue::QCborValue(const QRegularExpression &rx)

Creates a QCborValue object of the regular expression pattern extended type and containing the value represented by rx. The value can later be retrieved using toRegularExpression().

The CBOR regular expression type is an extended type represented by a string tagged as an RegularExpression. Note that CBOR regular expressions only store the patterns, so any flags that the QRegularExpression object may carry will be lost.

See also toRegularExpression(), isRegularExpression(), and taggedValue().

### QCborValue::QCborValue(const QString &s)

Creates a QCborValue with string value s. The value can later be retrieved using toString().

See also toString(), isString(), and isByteArray().

### `[explicit]` QCborValue::QCborValue(const QUrl &url)

Creates a QCborValue object of the URL extended type and containing the value represented by url. The value can later be retrieved using toUrl().

The CBOR URL type is an extended type represented by a string tagged as an Url.

See also toUrl(), isUrl(), and taggedValue().

### `[explicit]` QCborValue::QCborValue(const QUuid &uuid)

Creates a QCborValue object of the UUID extended type and containing the value represented by uuid. The value can later be retrieved using toUuid().

The CBOR UUID type is an extended type represented by a byte array tagged as an Uuid.

See also toUuid(), isUuid(), and taggedValue().

### QCborValue::QCborValue(double d)

Creates a QCborValue with floating point value d. The value can later be retrieved using toDouble().

CBOR floating point values are distinct from integer values. Therefore, QCborValue objects with integers will compare differently to QCborValue objects containing floating-point, even if the values contained in the objects are equivalent.

See also toDouble(), isDouble(), and isInteger().

### QCborValue::QCborValue(qint64 i)

Creates a QCborValue with integer value i. The value can later be retrieved using toInteger().

CBOR integer values are distinct from floating point values. Therefore, QCborValue objects with integers will compare differently to QCborValue objects containing floating-point, even if the values contained in the objects are equivalent.

See also toInteger(), isInteger(), and isDouble().

### QCborValue::QCborValue(QLatin1StringView s)

This is an overloaded function.

Creates a QCborValue with the Latin-1 string viewed by s. The value can later be retrieved using toString().

See also toString(), isString(), and isByteArray().

### `[noexcept]` QCborValue::QCborValue(const QCborValue &other)

Copies the contents of other into this object.

### `[noexcept]` QCborValue::QCborValue(QCborValue &&other)

This is an overloaded function.

Moves the contents of the other QCborValue object into this one and frees the resources of this one.

### `[noexcept]` QCborValue::~QCborValue()

Disposes of the current QCborValue object and frees any associated resources.

### int QCborValue::compare(const QCborValue &other) const

Compares this value and other, and returns an integer that indicates whether this value should be sorted prior to (if the result is negative) or after other (if the result is positive). If this function returns 0, the two values are equal and hold the same contents.

If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

###### Extended types

QCborValue compares equal a QCborValue containing an extended type, like Url and Url and its equivalent tagged representation. So, for example, the following expression is true:

         QCborValue(QUrl("https://example.com")) == QCborValue(QCborKnownTags::Url, "https://example.com");

Do note that Qt types like QUrl and QDateTime will normalize and otherwise modify their arguments. The expression above is true only because the string on the right side is the normalized value that the QCborValue on the left would take. If, for example, the "https" part were uppercase in both sides, the comparison would fail. For information on normalizations performed by QCborValue, please consult the documentation of the constructor taking the Qt type in question.

###### Sorting order

Sorting order in CBOR is defined in RFC 7049, section 3.9, which discusses the sorting of keys in a map when following the Canonical encoding. According to the specification, "sorting is performed on the bytes of the representation of the key data items" and lists as consequences that:

- "If two keys have different lengths, the shorter one sorts earlier;"
- "If two keys have the same length, the one with the lower value in (byte-wise) lexical order sorts earlier."

This results in surprising sorting of QCborValues, where the result of this function is different from that which would later be retrieved by comparing the contained elements. For example, the QCborValue containing string "zzz" sorts before the QCborValue with string "foobar", even though when comparing as QStrings or QByteArrays the "zzz" sorts after "foobar" (dictionary order).

The specification does not clearly indicate what sorting order should be done for values of different types (it says sorting should not pay "attention to the 3/5 bit splitting for major types"). QCborValue makes the assumption that types should be sorted too. The numeric values of the QCborValue::Type enumeration are in that order, with the exception of the extended types, which compare as their tagged equivalents.

Note: Sorting order is preliminary and is subject to change. Applications should not depend on the order returned by this function for the time being.

See also QCborArray::compare(), QCborMap::compare(), and operator==().

### `[static]` QCborValue QCborValue::fromCbor(QCborStreamReader &reader)

Decodes one item from the CBOR stream found in reader and returns the equivalent representation. This function is recursive: if the item is a map or array, it will decode all items found in that map or array, until the outermost object is finished.

This function need not be used on the root element of a QCborStreamReader. For example, the following code illustrates how to skip the CBOR signature tag from the beginning of a file:

         if (reader.isTag() && reader.toTag() == QCborKnownTags::Signature)
             reader.next();

         QCborValue contents = QCborValue::fromCbor(reader);

The returned value may be partially complete and indistinguishable from a valid QCborValue even if the decoding failed. To determine if there was an error, check if reader.lastError() is indicating an error condition. This function stops decoding immediately after the first error.

See also toCbor(), toDiagnosticNotation(), toVariant(), and toJsonValue().

### `[static]` QCborValue QCborValue::fromCbor(const QByteArray &ba, QCborParserError *error = nullptr)

This is an overloaded function.

Decodes one item from the CBOR stream found in the byte array ba and returns the equivalent representation. This function is recursive: if the item is a map or array, it will decode all items found in that map or array, until the outermost object is finished.

This function stores the error state, if any, in the object pointed to by error, along with the offset of where the error occurred. If no error happened, it stores NoError in the error state and the number of bytes that it consumed (that is, it stores the offset for the first unused byte). Using that information makes it possible to parse further data that may exist in the same byte array.

The returned value may be partially complete and indistinguishable from a valid QCborValue even if the decoding failed. To determine if there was an error, check if there was an error stored in error. This function stops decoding immediately after the first error.

See also toCbor(), toDiagnosticNotation(), toVariant(), and toJsonValue().

### `[static]` QCborValue QCborValue::fromJsonValue(const QJsonValue &v)

Converts the JSON value contained in v into its corresponding CBOR value and returns it. There is no data loss in converting from JSON to CBOR, as the CBOR type set is richer than JSON's. Additionally, values converted to CBOR using this function can be converted back to JSON using toJsonValue() with no data loss.

The following table lists the mapping of JSON types to CBOR types:

JSON Type | CBOR Type
--- | ---
Bool | Bool
Number | Integer (if the number has no fraction and is in the qint64 range) or Double
String | String
Array | Array
Object | Map
Null | Null

QJsonValue can also be undefined, indicating a previous operation that failed to complete (for example, searching for a key not present in an object). Undefined values are not JSON types and may not appear in JSON arrays and objects, but this function does return the QCborValue undefined value if the corresponding QJsonValue is undefined.

See also toJsonValue(), fromVariant(), QCborArray::fromJsonArray(), and QCborMap::fromJsonObject().

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

Converts the QVariant variant into QCborValue and returns it.

QVariants may contain a large list of different meta types, many of which have no corresponding representation in CBOR. That includes all user-defined meta types. When preparing transmission using CBOR, it is suggested to encode carefully each value to prevent loss of representation.

The following table lists the conversion this function will apply:

Qt (C++) type | CBOR type
--- | ---
invalid (QVariant()) | Undefined
`bool` | Bool
`std::nullptr_t` | Null
`short`, `ushort`, `int`, `uint`, qint64 | Integer
quint64 | Integer, or Double if outside the range of qint64
`float`, `double` | Double
QByteArray | ByteArray
QDateTime | DateTime
QCborSimpleType | Simple type
QJsonArray | Array, converted using QCborArray::formJsonArray()
QJsonDocument | Array or Map
QJsonObject | Map, converted using QCborMap::fromJsonObject()
QJsonValue | converted using fromJsonValue()
QRegularExpression | RegularExpression
QString | String
QStringList | Array
QVariantHash | Map
QVariantList | Array
QVariantMap | Map
QUrl | Url
QUuid | Uuid

If QVariant::isNull() returns true, a null QCborValue 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.

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 an Undefined CBOR value. Note that QVariant::toString() is also lossy for the majority of types.

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

See also toVariant(), fromJsonValue(), QCborArray::toVariantList(), QCborMap::toVariantMap(), and QJsonValue::fromVariant().

### bool QCborValue::isArray() const

Returns true if this QCborValue is of the array type. The array value can be retrieved using toArray().

See also type() and toArray().

### bool QCborValue::isBool() const

Returns true if this QCborValue is a boolean. The value can be retrieved using toBool().

See also type(), toBool(), isTrue(), and isFalse().

### bool QCborValue::isByteArray() const

Returns true if this QCborValue is of the byte array type. The byte array value can be retrieved using toByteArray().

See also type() and toByteArray().

### bool QCborValue::isContainer() const

This convenience function returns true if the QCborValue is either an array or a map.

See also isArray() and isMap().

### bool QCborValue::isDateTime() const

Returns true if this QCborValue is of the date/time type. The value can be retrieved using toDateTime(). Date/times are extended types that use the tag DateTime.

Additionally, when decoding from a CBOR stream, QCborValue will interpret tags of value UnixTime_t and convert them to the equivalent date/time.

See also type() and toDateTime().

### bool QCborValue::isDouble() const

Returns true if this QCborValue is of the floating-point type. The value can be retrieved using toDouble().

See also type() and toDouble().

### bool QCborValue::isFalse() const

Returns true if this QCborValue is a boolean with false value. This function exists because, internally, CBOR booleans are stored as two separate types, one for true and one for false.

See also type(), isBool(), isTrue(), and toBool().

### bool QCborValue::isInteger() const

Returns true if this QCborValue is of the integer type. The integer value can be retrieved using toInteger().

See also type() and toInteger().

### bool QCborValue::isInvalid() const

Returns true if this QCborValue is not of any valid type. Invalid QCborValues are distinct from those with undefined values and they usually represent a decoding error.

See also isUndefined() and isNull().

### bool QCborValue::isMap() const

Returns true if this QCborValue is of the map type. The map value can be retrieved using toMap().

See also type() and toMap().

### bool QCborValue::isNull() const

Returns true if this QCborValue is of the null type.

CBOR null values are used to indicate optional values that were not provided. They are distinct from undefined values, in that null values are usually not the result of an earlier error or problem.

Null values are distinct from undefined values and from invalid QCborValue objects. The API will not create invalid QCborValues, but they may exist as a result of a parsing error.

See also type(), isUndefined(), and isInvalid().

### bool QCborValue::isRegularExpression() const

Returns true if this QCborValue contains a regular expression's pattern. The pattern can be retrieved using toRegularExpression().

See also type() and toRegularExpression().

### bool QCborValue::isSimpleType() const

Returns true if this QCborValue is of one of the CBOR simple types. The type itself can later be retrieved using type(), even for types that don't have an enumeration in the API. They can also be checked with the isSimpleType(QCborSimpleType) overload.

See also QCborSimpleType, isSimpleType(QCborSimpleType), and toSimpleType().

### bool QCborValue::isSimpleType(QCborSimpleType st) const

This is an overloaded function.

Returns true if this QCborValue is of a simple type and toSimpleType() would return st, false otherwise. This function can be used to check for any CBOR simple type, even those for which there is no enumeration in the API. For example, for the simple type of value 12, you could write:

         value.isSimpleType(QCborSimpleType(12));

See also QCborValue::QCborValue(QCborSimpleType), isSimpleType(), isFalse(), isTrue(), isNull, isUndefined(), and toSimpleType().

### bool QCborValue::isString() const

Returns true if this QCborValue is of the string type. The string value can be retrieved using toString().

See also type() and toString().

### bool QCborValue::isTag() const

Returns true if this QCborValue is of the tag type. The tag value can be retrieved using tag() and the tagged value using taggedValue().

This function also returns true for extended types that the API recognizes. For code that handles extended types directly before the Qt API is updated to support them, it is possible to recreate the tag + tagged value pair by using taggedValue().

See also type(), tag(), taggedValue(), and taggedValue().

### bool QCborValue::isTrue() const

Returns true if this QCborValue is a boolean with true value. This function exists because, internally, CBOR booleans are stored as two separate types, one for false and one for true.

See also type(), isBool(), isFalse(), and toBool().

### bool QCborValue::isUndefined() const

Returns true if this QCborValue is of the undefined type.

CBOR undefined values are used to indicate missing information, usually as a result of a previous operation that did not complete as expected. They are also used by the QCborArray and QCborMap API to indicate the searched item was not found.

Undefined values are distinct from null values.

QCborValue objects with undefined values are also different from invalid QCborValue objects. The API will not create invalid QCborValues, but they may exist as a result of a parsing error.

See also type(), isNull(), and isInvalid().

### bool QCborValue::isUrl() const

Returns true if this QCborValue is of the URL type. The URL value can be retrieved using toUrl().

See also type() and toUrl().

### bool QCborValue::isUuid() const

Returns true if this QCborValue contains a UUID. The value can be retrieved using toUuid().

See also type() and toUuid().

### `[noexcept]` void QCborValue::swap(QCborValue &other)

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

### QCborTag QCborValue::tag(QCborTag defaultValue = QCborTag(-1)) const

Returns the tag of this extended QCborValue object, if it is of the tag type, defaultValue otherwise.

CBOR represents extended types by associating a number (the tag) with a stored representation. This function returns that number. To retrieve the representation, use taggedValue().

See also isTag(), taggedValue(), isDateTime(), isUrl(), isRegularExpression(), and isUuid().

### QCborValue QCborValue::taggedValue(const QCborValue &defaultValue = QCborValue()) const

Returns the tagged value of this extended QCborValue object, if it is of the tag type, defaultValue otherwise.

CBOR represents extended types by associating a number (the tag) with a stored representation. This function returns that representation. To retrieve the tag, use tag().

See also isTag(), tag(), isDateTime(), isUrl(), isRegularExpression(), and isUuid().

### bool QCborValue::toBool(bool defaultValue = false) const

Returns the boolean value stored in this QCborValue, if it is of a boolean type. Otherwise, it returns defaultValue.

See also isBool(), isTrue(), and isFalse().

### QByteArray QCborValue::toByteArray(const QByteArray &defaultValue = {}) const

Returns the byte array value stored in this QCborValue, if it is of the byte array type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QByteArray.

See also isByteArray(), isString(), and toString().

### QByteArray QCborValue::toCbor(QCborValue::EncodingOptions opt = NoTransformation) const

Encodes this QCborValue object to its CBOR representation, using the options specified in opt, and return the byte array containing that representation.

This function will not fail, except if this QCborValue or any of the contained items, if this is a map or array, are invalid. Invalid types are not produced normally by the API, but can result from decoding errors.

By default, this function performs no transformation on the values in the QCborValue, writing all floating point directly as double-precision (`double`) types. If the UseFloat option is specified, it will use single precision (`float`) for any floating point value for which there's no loss of precision in using that representation. That includes infinities and NaN values.

Similarly, if UseFloat16 is specified, this function will try to use half-precision (`qfloat16`) floating point if the conversion to that results in no loss of precision. This is always true for infinities and NaN.

If UseIntegers is specified, it will use integers for any floating point value that contains an actual integer.

See also fromCbor(), fromVariant(), and fromJsonValue().

### void QCborValue::toCbor(QCborStreamWriter &writer, QCborValue::EncodingOptions opt = NoTransformation) const

This is an overloaded function.

Encodes this QCborValue object to its CBOR representation, using the options specified in opt, to the writer specified by writer. The same writer can be used by multiple QCborValues, for example, in order to encode different elements in a larger array.

This function will not fail, except if this QCborValue or any of the contained items, if this is a map or array, are invalid. Invalid types are not produced normally by the API, but can result from decoding errors.

By default, this function performs no transformation on the values in the QCborValue, writing all floating point directly as double-precision (binary64) types. If the UseFloat option is specified, it will use single precision (binary32) for any floating point value for which there's no loss of precision in using that representation. That includes infinities and NaN values.

Similarly, if UseFloat16 is specified, this function will try to use half-precision (binary16) floating point if the conversion to that results in no loss of precision. This is always true for infinities and NaN.

If UseIntegers is specified, it will use integers for any floating point value that contains an actual integer.

See also fromCbor(), fromVariant(), and fromJsonValue().

### QDateTime QCborValue::toDateTime(const QDateTime &defaultValue = {}) const

Returns the date/time value stored in this QCborValue, if it is of the date/time extended type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QDateTime.

See also isDateTime(), isTag(), and taggedValue().

### QString QCborValue::toDiagnosticNotation(QCborValue::DiagnosticNotationOptions opts = Compact) const

Creates the diagnostic notation equivalent of this CBOR object and returns it. The opts parameter controls the dialect of the notation. Diagnostic notation is useful in debugging, to aid the developer in understanding what value is stored in the QCborValue or in a CBOR stream. For that reason, the Qt API provides no support for parsing the diagnostic back into the in-memory format or CBOR stream, though the representation is unique and it would be possible.

CBOR diagnostic notation is specified by section 6 of RFC 7049. It is a text representation of the CBOR stream and it is very similar to JSON, but it supports the CBOR types not found in JSON. The extended format enabled by the ExtendedFormat flag is currently in some IETF drafts and its format is subject to change.

This function produces the equivalent representation of the stream that toCbor() would produce, without any transformation option provided there. This also implies this function may not produce a representation of the stream that was used to create the object, if it was created using fromCbor(), as that function may have applied transformations. For a high-fidelity notation of a stream, without transformation, see the `cbordump` example.

See also toCbor() and QJsonDocument::toJson().

### double QCborValue::toDouble(double defaultValue = 0) const

Returns the floating point value stored in this QCborValue, if it is of the Double type. If it is of the Integer type, this function returns the integer value converted to double. In any other case, it returns defaultValue.

See also isDouble(), isInteger(), and toInteger().

### qint64 QCborValue::toInteger(qint64 defaultValue = 0) const

Returns the integer value stored in this QCborValue, if it is of the integer type. If it is of the Double type, this function returns the floating point value converted to integer. In any other case, it returns defaultValue.

See also isInteger(), isDouble(), and toDouble().

### QJsonValue QCborValue::toJsonValue() const

Converts this QCborValue object to an equivalent representation in JSON and returns it as a QJsonValue.

Please note that CBOR contains a richer and wider type set than JSON, so some information may be lost in this conversion. The following table compares CBOR types to JSON types and indicates whether information may be lost or not.

CBOR Type | JSON Type | Comments
--- | --- | ---
Bool | Bool | No data loss possible
Double | Number | Infinities and NaN will be converted to Null; no data loss for other values
Integer | Number | Data loss possible in the conversion if the integer is larger than 253 or smaller than -253.
Null | Null | No data loss possible
Undefined | Null | Type information lost
String | String | No data loss possible
Byte Array | String | Converted to a lossless encoding like Base64url, but the distinction between strings and byte arrays is lost
Other simple types | String | Type information lost
Array | Array | Conversion applies to each contained value
Map | Object | Keys are converted to string; values converted according to this table
Tags and extended types | Special | The tag number itself is lost and the tagged value is converted to JSON

For information on the conversion of CBOR map keys to string, see QCborMap::toJsonObject().

If this QCborValue contains the undefined value, this function will return an undefined QJsonValue too. Note that JSON does not support undefined values and undefined QJsonValues are an extension to the specification. They cannot be held in a QJsonArray or QJsonObject, but can be returned from functions to indicate a failure. For all other intents and purposes, they are the same as null.

###### Special handling of tags and extended types

Some tags are handled specially and change the transformation of the tagged value from CBOR to JSON. The following table lists those special cases:

Tag | CBOR type | Transformation
--- | --- | ---
ExpectedBase64url | Byte array | Encodes the byte array as Base64url
ExpectedBase64 | Byte array | Encodes the byte array as Base64
ExpectedBase16 | Byte array | Encodes the byte array as hex
Url | Url and String | Uses QUrl::toEncoded() to normalize the encoding to the URL's fully encoded format
Uuid | Uuid and Byte array | Uses QUuid::toString() to create the string representation

See also fromJsonValue(), toVariant(), QCborArray::toJsonArray(), and QCborMap::toJsonObject().

### QRegularExpression QCborValue::toRegularExpression(const QRegularExpression &defaultValue = {}) const

Returns the regular expression value stored in this QCborValue, if it is of the regular expression pattern extended type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QRegularExpression.

See also isRegularExpression(), isTag(), and taggedValue().

### QCborSimpleType QCborValue::toSimpleType(QCborSimpleType defaultValue = QCborSimpleType::Undefined) const

Returns the simple type this QCborValue is of, if it is a simple type. If it is not a simple type, it returns defaultValue.

The following types are simple types and this function will return the listed values:

QCborValue::False | QCborSimpleType::False
QCborValue::True | QCborSimpleType::True
QCborValue::Null | QCborSimpleType::Null
QCborValue::Undefined | QCborSimpleType::Undefined

See also type(), isSimpleType(), isBool(), isTrue(), isFalse(), isTrue(), isNull(), and isUndefined().

### QString QCborValue::toString(const QString &defaultValue = {}) const

Returns the string value stored in this QCborValue, if it is of the string type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QString.

See also isString(), isByteArray(), and toByteArray().

### QUrl QCborValue::toUrl(const QUrl &defaultValue = {}) const

Returns the URL value stored in this QCborValue, if it is of the URL extended type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QUrl.

See also isUrl(), isTag(), and taggedValue().

### QUuid QCborValue::toUuid(const QUuid &defaultValue = {}) const

Returns the UUID value stored in this QCborValue, if it is of the UUID extended type. Otherwise, it returns defaultValue.

Note that this function performs no conversion from other types to QUuid.

See also isUuid(), isTag(), and taggedValue().

### QVariant QCborValue::toVariant() const

Converts this value to a native Qt type and returns the corresponding QVariant.

The following table lists the mapping performed between QCborValue types and Qt meta types.

CBOR Type | Qt or C++ type | Notes
--- | --- | ---
Integer | qint64 |
Double | `double` |
Bool | `bool` |
Null | `std::nullptr_t` |
Undefined | no type (QVariant()) |
Byte array | QByteArray |
String | QString |
Array | QVariantList | Recursively converts all values
Map | QVariantMap | Key types are "stringified"
Other simple types | QCborSimpleType |
DateTime | QDateTime |
Url | QUrl |
RegularExpression | QRegularExpression |
Uuid | QUuid |
Other tags | Special | The tag is ignored and the tagged value is converted using this function

Note that values in both CBOR Maps and Arrays are converted recursively using this function too and placed in QVariantMap and QVariantList instead. You will not find QCborMap and QCborArray stored inside the QVariants.

QVariantMaps have string keys, unlike CBOR, so the conversion of a QCborMap to QVariantMap will imply a step of "stringification" of the key values. See QCborMap::toJsonObject() for details.

See also fromVariant(), toJsonValue(), QCborArray::toVariantList(), and QCborMap::toVariantMap().

### QCborValue::Type QCborValue::type() const

Returns the type of this QCborValue. The type can also later be retrieved by one of the "isXxx" functions.

See also isInteger(), isByteArray(), isString(), isArray(), isMap(), isTag(), isFalse(), isTrue(), isBool(), isNull(), isUndefined, isDouble(), isDateTime(), isUrl(), isRegularExpression(), and isUuid().

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

Replaces the contents of this QCborObject with a copy of other.

### `[noexcept]` QCborValue &QCborValue::operator=(QCborValue &&other)

This is an overloaded function.

Moves the contents of the other QCborValue object into this one and frees the resources of this one. Returns a reference to this object.

### QCborValueRef QCborValue::operator[](const QString &key)

Returns a QCborValueRef that can be used to read or modify the entry in this, as a map, with the given key. When this QCborValue is a QCborMap, this function is equivalent to the matching operator[] on that map.

Before returning the reference: if this QCborValue was an array, it is first converted to a map (so that `map[i]` is `array[i]` for each index, `i`, with valid `array[i]`); otherwise, if it was not a map it will be over-written with an empty map.

See also operator[](qint64), QCborMap::operator[], QCborMap::value(), and QCborMap::find().

### const QCborValue QCborValue::operator[](const QString &key) const

If this QCborValue is a QCborMap, searches elements for the value whose key matches key. If there's no key matching key in the map or if this QCborValue object is not a map, returns the undefined value.

This function is equivalent to:

         value.toMap().value(key);

See also operator[](qint64), QCborMap::operator[], QCborMap::value(), and QCborMap::find().

### QCborValueRef QCborValue::operator[](QLatin1StringView key)

This is an overloaded function.

Returns a QCborValueRef that can be used to read or modify the entry in this, as a map, with the given key. When this QCborValue is a QCborMap, this function is equivalent to the matching operator[] on that map.

Before returning the reference: if this QCborValue was an array, it is first converted to a map (so that `map[i]` is `array[i]` for each index, `i`, with valid `array[i]`); otherwise, if it was not a map it will be over-written with an empty map.

See also operator[](qint64), QCborMap::operator[], QCborMap::value(), and QCborMap::find().

### QCborValueRef QCborValue::operator[](qint64 key)

This is an overloaded function.

Returns a QCborValueRef that can be used to read or modify the entry in this, as a map or array, with the given key. When this QCborValue is a QCborMap or, for 0 <= key < 0x10000, a QCborArray, this function is equivalent to the matching operator[] on that map or array.

Before returning the reference: if this QCborValue was an array but the key is out of range, the array is first converted to a map (so that `map[i]` is `array[i]` for each index, `i`, with valid `array[i]`); otherwise, if it was not a map it will be over-written with an empty map.

See also operator[], QCborMap::operator[], QCborMap::value(), QCborMap::find(), QCborArray::operator[], and QCborArray::at().

### const QCborValue QCborValue::operator[](QLatin1StringView key) const

This is an overloaded function.

If this QCborValue is a QCborMap, searches elements for the value whose key matches key. If there's no key matching key in the map or if this QCborValue object is not a map, returns the undefined value.

This function is equivalent to:

         value.toMap().value(key);

See also operator[](qint64), QCborMap::operator[], QCborMap::value(), and QCborMap::find().

### const QCborValue QCborValue::operator[](qint64 key) const

This is an overloaded function.

If this QCborValue is a QCborMap, searches elements for the value whose key matches key. If this is a QCborArray, returns the element whose index is key. If there's no matching value in the array or map, or if this QCborValue object is not an array or map, returns the undefined value.

See also operator[], QCborMap::operator[], QCborMap::value(), QCborMap::find(), QCborArray::operator[], and QCborArray::at().

## Related Non-Members

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

Compares lhs and rhs, and returns true if contents differ, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR equality in Qt, see, QCborValue::compare().

See also compare(), QCborValue::operator==(), QCborMap::operator==(), operator==(), and operator<().

### `[noexcept]` bool operator<(const QCborValue &lhs, const QCborValue &rhs)

Compares lhs and rhs, and returns true if lhs should be sorted before rhs, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR sorting order, see QCborValue::compare().

See also compare(), QCborValue::operator==(), QCborMap::operator==(), operator==(), and operator!=().

### `[noexcept]` bool operator<=(const QCborValue &lhs, const QCborValue &rhs)

Compares lhs and rhs, and returns true if lhs should be sorted before rhs or is being equal to rhs, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR sorting order, see QCborValue::compare().

See also compare(), QCborValue::operator<(), QCborMap::operator==(), operator==(), and operator!=().

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

Compares lhs and rhs, and returns true if they hold the same contents, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR equality in Qt, see, compare().

See also compare(), QCborValue::operator==(), QCborMap::operator==(), operator!=(), and operator<().

### `[noexcept]` bool operator>(const QCborValue &lhs, const QCborValue &rhs)

Compares lhs and rhs, and returns true if lhs should be sorted after rhs, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR sorting order, see QCborValue::compare().

See also compare(), QCborValue::operator>=(), QCborMap::operator==(), operator==(), and operator!=().

### `[noexcept]` bool operator>=(const QCborValue &lhs, const QCborValue &rhs)

Compares lhs and rhs, and returns true if lhs should be sorted after rhs or is being equal to rhs, false otherwise. If each QCborValue contains an array or map, the comparison is recursive to elements contained in them.

For more information on CBOR sorting order, see QCborValue::compare().

See also compare(), QCborValue::operator>(), QCborMap::operator==(), operator==(), and operator!=().