class QCborValue#

The QCborValue class encapsulates a value in CBOR. More…

Synopsis#

Methods#

Static functions#

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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 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 None. 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 (-2 63) to 9,223,372,036,854,775,807 (2 63 - 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}

class EncodingOption#

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

Constant

Description

QCborValue.NoTransformation

(Default) Performs no transformations.

QCborValue.UseFloat

Tells the encoder to use IEEE 754 single-precision floating point (that is, float) whenever possible.

QCborValue.UseFloat16

Tells the encoder to use IEEE 754 half-precision floating point (that is, qfloat16), whenever possible. Implies UseFloat.

QCborValue.UseIntegers

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.

See also

toCbor()

class DiagnosticNotationOption#

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

Constant

Description

QCborValue.Compact

Does not use any line-breaks, producing a compact representation.

QCborValue.LineWrapped

Uses line-breaks, one QCborValue per line.

QCborValue.ExtendedFormat

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, toCbor() will either use hex with spaces, base64 or base64url encoding, depending on the context.

class Type#

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

The CBOR built-in types are:

Constant

Description

QCborValue.Integer

qint64: An integer value

QCborValue.ByteArray

QByteArray : a byte array (“byte string”)

QCborValue.String

QString : a Unicode string (“text string”)

QCborValue.Array

QCborArray : an array of QCborValues

QCborValue.Map

QCborMap : an associative container of QCborValues

QCborValue.SimpleType

QCborSimpleType : one of several simple types/values

QCborValue.False

bool: the simple type for value false

QCborValue.True

bool: the simple type for value true

QCborValue.Null

std::nullptr_t: the simple type for the null value

QCborValue.Undefined

(no type) the simple type for the undefined value

QCborValue.Double

double: a double-precision floating point

QCborValue.Invalid

Not a valid value, this usually indicates a CBOR decoding error

Additionally, QCborValue can represent extended types:

Constant

Description

QCborValue.Tag

An unknown or unrecognized extended type, represented by its tag (a QCborTag ) and the tagged value (a QCborValue )

QCborValue.DateTime

QDateTime : a date and time stamp

QCborValue.Url

QUrl : a URL or URI

QCborValue.RegularExpression

QRegularExpression : the pattern of a regular expression

QCborValue.Uuid

QUuid : a UUID

See also

type()

__init__(i)#
Parameters:

i – int

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.

__init__()

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.

__init__(u)
Parameters:

u – int

__init__(i)
Parameters:

i – int

__init__(v)
Parameters:

v – float

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.

__init__(s)
Parameters:

s – str

__init__(uuid)
Parameters:

uuid – QUuid

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 .

__init__(url)
Parameters:

url – QUrl

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 .

__init__(s)
Parameters:

s – str

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

__init__(rx)
Parameters:

rx – QRegularExpression

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.

__init__(dt)
Parameters:

dt – QDateTime

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.

__init__(m)
Parameters:

m – QCborMap

__init__(t_[, tv=QCborValue()])
Parameters:

This is an overloaded function.

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

__init__(st)
Parameters:

st – QCborSimpleType

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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 None.

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:

value = QCborValue(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()

__init__(tag[, taggedValue=QCborValue()])
Parameters:
__init__(t_)
Parameters:

t – Type

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

See also

type()

__init__(s)
Parameters:

s – QLatin1String

__init__(b_)
Parameters:

b – bool

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).

__init__(other)
Parameters:

other – QCborValue

Copies the contents of other into this object.

__init__(a)
Parameters:

a – QCborArray

__init__(ba)
Parameters:

ba – QByteArray

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

__init__(s)
Parameters:

s – str

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

compare(other)#
Parameters:

other – QCborValue

Return type:

int

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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 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

compare() compare() operator==()

static fromCbor(reader)#
Parameters:

reader – QCborStreamReader

Return type:

QCborValue

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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() and reader.toTag() == QCborKnownTags.Signature:
    reader.next()
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 lastError() is indicating an error condition. This function stops decoding immediately after the first error.

static fromCbor(ba[, error=None])
Parameters:
Return type:

QCborValue

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.

static fromCbor(data, len[, error=None])
Parameters:
Return type:

QCborValue

static fromCbor(data, len[, error=None])
Parameters:
Return type:

QCborValue

static fromJsonValue(v)#
Parameters:

v – QJsonValue

Return type:

QCborValue

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.

static fromVariant(variant)#
Parameters:

variant – object

Return type:

QCborValue

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 fromJsonObject()

QJsonValue

converted using fromJsonValue()

QRegularExpression

RegularExpression

QString

String

QStringList

Array

QVariantHash

Map

QVariantList

Array

QVariantMap

Map

QUrl

Url

QUuid

Uuid

If 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 isNull() also affects this function.

For other types not listed above, a conversion to string will be attempted, usually but not always by calling toString() . If the conversion fails the value is replaced by an Undefined CBOR value. Note that toString() is also lossy for the majority of types.

Please note that the conversions via 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.

isArray()#
Return type:

bool

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

See also

type() toArray()

isBool()#
Return type:

bool

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

isByteArray()#
Return type:

bool

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

isContainer()#
Return type:

bool

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

See also

isArray() isMap()

isDateTime()#
Return type:

bool

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() toDateTime()

isDouble()#
Return type:

bool

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

See also

type() toDouble()

isFalse()#
Return type:

bool

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.

isInteger()#
Return type:

bool

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

See also

type() toInteger()

isInvalid()#
Return type:

bool

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.

isMap()#
Return type:

bool

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

See also

type() toMap()

isNull()#
Return type:

bool

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.

isRegularExpression()#
Return type:

bool

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

isSimpleType()#
Return type:

bool

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) toSimpleType()

isSimpleType(st)
Parameters:

st – QCborSimpleType

Return type:

bool

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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(QCborSimpleType) isSimpleType() isFalse() isTrue() isNull isUndefined() toSimpleType()

isString()#
Return type:

bool

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

See also

type() toString()

isTag()#
Return type:

bool

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() .

isTrue()#
Return type:

bool

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.

isUndefined()#
Return type:

bool

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.

isUrl()#
Return type:

bool

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

See also

type() toUrl()

isUuid()#
Return type:

bool

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

See also

type() toUuid()

__ne__(other)#
Parameters:

other – QCborValue

Return type:

bool

Compares this value and other, 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, compare() .

See also

compare() operator==() operator==() operator==() operator

__lt__(other)#
Parameters:

other – QCborValue

Return type:

bool

Compares this value and other, and returns true if this value should be sorted before other, 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 compare() .

See also

compare() operator==() operator==() operator==() operator!=()

__eq__(other)#
Parameters:

other – QCborValue

Return type:

bool

Compares this value and other, 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() operator==() operator!=() operator

operator(key)#
Parameters:

key – QLatin1String

Return type:

QCborValue

operator(key)
Parameters:

key – str

Return type:

QCborValue

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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) operator[] value() find()

operator(key)
Parameters:

key – int

Return type:

QCborValue

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[] operator[] value() find() operator[] at()

swap(other)#
Parameters:

other – QCborValue

Swaps the contents of this QCborValue object and other.

tag([defaultValue=QCborTag(-1)])#
Parameters:

defaultValue – QCborTag

Return type:

QCborTag

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() .

taggedValue([defaultValue=QCborValue()])#
Parameters:

defaultValue – QCborValue

Return type:

QCborValue

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() .

toArray(defaultValue)#
Parameters:

defaultValue – QCborArray

Return type:

QCborArray

toArray()
Return type:

QCborArray

toBool([defaultValue=false])#
Parameters:

defaultValue – bool

Return type:

bool

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

toByteArray([defaultValue={}])#
Parameters:

defaultValue – QByteArray

Return type:

QByteArray

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 .

toCbor(writer[, opt=QCborValue.EncodingOption.NoTransformation])#
Parameters:

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.

toCbor([opt=QCborValue.EncodingOption.NoTransformation])
Parameters:

opt – Combination of EncodingOption

Return type:

QByteArray

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.

toDateTime([defaultValue={}])#
Parameters:

defaultValue – QDateTime

Return type:

QDateTime

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 .

toDiagnosticNotation([opts=QCborValue.DiagnosticNotationOption.Compact])#
Parameters:

opts – Combination of DiagnosticNotationOption

Return type:

str

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() toJson()

toDouble([defaultValue=0])#
Parameters:

defaultValue – float

Return type:

float

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.

toInteger([defaultValue=0])#
Parameters:

defaultValue – int

Return type:

int

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.

toJsonValue()#
Return type:

QJsonValue

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 2 53 or smaller than -2 53.

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 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 toEncoded() to normalize the encoding to the URL’s fully encoded format

Uuid

Uuid and Byte array

Uses toString() to create the string representation

See also

fromJsonValue() toVariant() toJsonArray() toJsonObject()

toMap()#
Return type:

QCborMap

toMap(defaultValue)
Parameters:

defaultValue – QCborMap

Return type:

QCborMap

toRegularExpression([defaultValue={}])#
Parameters:

defaultValue – QRegularExpression

Return type:

QRegularExpression

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 .

toSimpleType([defaultValue=QCborSimpleType.Undefined])#
Parameters:

defaultValue – QCborSimpleType

Return type:

QCborSimpleType

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:

toString([defaultValue={}])#
Parameters:

defaultValue – str

Return type:

str

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 .

toUrl([defaultValue={}])#
Parameters:

defaultValue – QUrl

Return type:

QUrl

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 .

toUuid([defaultValue={}])#
Parameters:

defaultValue – QUuid

Return type:

QUuid

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 .

toVariant()#
Return type:

object

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 toJsonObject() for details.

type()#
Return type:

Type

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