- Qt 6.9
- Qt Core
- C++ Classes
- QUuid
- Qt 6.9.3 Reference Documentation

# QUuid Class

The QUuid class stores a Universally Unique Identifier (UUID). More...

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

- List of all members, including inherited members

This class is strongly comparable.

This class is strongly comparable with GUID.

Note: Comparison with GUID is Windows-only.

Note: All functions in this class are reentrant.

## Public Types

`(since 6.6)` union | Id128Bytes
enum | StringFormat { WithBraces, WithoutBraces, Id128 }
enum | Variant { VarUnknown, NCS, DCE, Microsoft, Reserved }
enum | Version { VerUnknown, Time, EmbeddedPOSIX, Name, Md5, …, UnixEpoch }

## Public Functions

| QUuid()
| QUuid(QAnyStringView text)
| QUuid(const GUID &guid)
`(since 6.6)` | QUuid(QUuid::Id128Bytes id128, QSysInfo::Endian order = QSysInfo::BigEndian)
| QUuid(uint l, ushort w1, ushort w2, uchar b1, uchar b2, uchar b3, uchar b4, uchar b5, uchar b6, uchar b7, uchar b8)
bool | isNull() const
QByteArray | toByteArray(QUuid::StringFormat mode = WithBraces) const
`(since 6.6)` QUuid::Id128Bytes | toBytes(QSysInfo::Endian order = QSysInfo::BigEndian) const
CFUUIDRef | toCFUUID() const
NSUUID * | toNSUUID() const
QByteArray | toRfc4122() const
QString | toString(QUuid::StringFormat mode = WithBraces) const
`(since 6.6)` quint128 | toUInt128(QSysInfo::Endian order = QSysInfo::BigEndian) const
QUuid::Variant | variant() const
QUuid::Version | version() const
GUID | operator GUID() const
QUuid & | operator=(const GUID &guid)

## Static Public Members

QUuid | createUuid()
QUuid | createUuidV3(QUuid ns, QByteArrayView baseData)
QUuid | createUuidV3(const QUuid &ns, const QString &baseData)
QUuid | createUuidV5(QUuid ns, QByteArrayView baseData)
QUuid | createUuidV5(const QUuid &ns, const QString &baseData)
`(since 6.9)` QUuid | createUuidV7()
`(since 6.6)` QUuid | fromBytes(const void *bytes, QSysInfo::Endian order = QSysInfo::BigEndian)
QUuid | fromCFUUID(CFUUIDRef uuid)
QUuid | fromNSUUID(const NSUUID *uuid)
QUuid | fromRfc4122(QByteArrayView bytes)
QUuid | fromString(QAnyStringView string)
`(since 6.6)` QUuid | fromUInt128(quint128 uuid, QSysInfo::Endian order = QSysInfo::BigEndian)

## Related Non-Members

size_t | qHash(const QUuid &key, size_t seed = 0)
bool | operator!=(const QUuid &lhs, const GUID &rhs)
bool | operator!=(const QUuid &lhs, const QUuid &rhs)
bool | operator<(const QUuid &lhs, const QUuid &rhs)
QDataStream & | operator<<(QDataStream &s, const QUuid &id)
QDebug | operator<<(QDebug dbg, const QUuid &id)
bool | operator<=(const QUuid &lhs, const QUuid &rhs)
bool | operator==(const QUuid &lhs, const GUID &rhs)
bool | operator==(const QUuid &lhs, const QUuid &rhs)
bool | operator>(const QUuid &lhs, const QUuid &rhs)
bool | operator>=(const QUuid &lhs, const QUuid &rhs)
QDataStream & | operator>>(QDataStream &s, QUuid &id)

## Detailed Description

Using Universally Unique IDentifiers (UUID) is a standard way to uniquely identify entities in a distributed computing environment. A UUID is a 16-byte (128-bit) number generated by some algorithm that is meant to guarantee that the UUID will be unique in the distributed computing environment where it is used. The acronym GUID is often used instead, Globally Unique IDentifiers, but it refers to the same thing.

Actually, the GUID is one variant of UUID. Multiple variants are in use. Each UUID contains a bit field that specifies which type (variant) of UUID it is. Call variant() to discover which type of UUID an instance of QUuid contains. It extracts the three most significant bits of byte 8 of the 16 bytes. In QUuid, byte 8 is `QUuid::data4[0]`. If you create instances of QUuid using the constructor that accepts all the numeric values as parameters, use the following table to set the three most significant bits of parameter `b1`, which becomes `QUuid::data4[0]` and contains the variant field in its three most significant bits. In the table, 'x' means don't care.

msb0 | msb1 | msb2 | Variant
--- | --- | --- | ---
0 | x | x | NCS (Network Computing System)
1 | 0 | x | DCE (Distributed Computing Environment)
1 | 1 | 0 | Microsoft (GUID)
1 | 1 | 1 | Reserved for future expansion

If variant() returns QUuid::DCE, the UUID also contains a version field in the four most significant bits of `QUuid::data3`, and you can call version() to discover which version your QUuid contains. If you create instances of QUuid using the constructor that accepts all the numeric values as parameters, use the following table to set the four most significant bits of parameter `w2`, which becomes `QUuid::data3` and contains the version field in its four most significant bits.

msb0 | msb1 | msb2 | msb3 | Version
--- | --- | --- | --- | ---
0 | 0 | 0 | 1 | Time
0 | 0 | 1 | 0 | Embedded POSIX
0 | 0 | 1 | 1 | Md5(Name)
0 | 1 | 0 | 0 | Random
0 | 1 | 0 | 1 | Sha1

The field layouts for the DCE versions listed in the table above are specified in the Network Working Group UUID Specification.

Most platforms provide a tool for generating new UUIDs, e.g. `uuidgen` and `guidgen`. You can also use createUuid(). UUIDs generated by createUuid() are of the random type. Their QUuid::Version bits are set to QUuid::Random, and their QUuid::Variant bits are set to QUuid::DCE. The rest of the UUID is composed of random numbers. Theoretically, this means there is a small chance that a UUID generated by createUuid() will not be unique. But it is a very small chance.

UUIDs can be constructed from numeric values or from strings, or using the static createUuid() function. They can be converted to a string with toString(). UUIDs have a variant() and a version(), and null UUIDs return true from isNull().

## Member Type Documentation

### enum QUuid::StringFormat

This enum is used by toString(StringFormat) to control the formatting of the string representation. The possible values are:

Constant | Value | Description
--- | --- | ---
`QUuid::WithBraces` | `0` | The default, toString() will return five hex fields, separated by dashes and surrounded by braces. Example: {00000000-0000-0000-0000-000000000000}.
`QUuid::WithoutBraces` | `1` | Only the five dash-separated fields, without the braces. Example: 00000000-0000-0000-0000-000000000000.
`QUuid::Id128` | `3` | Only the hex digits, without braces or dashes. Note that QUuid cannot parse this back again as input.

### enum QUuid::Variant

This enum defines the values used in the variant field of the UUID. The value in the variant field determines the layout of the 128-bit value.

Constant | Value | Description
--- | --- | ---
`QUuid::VarUnknown` | `-1` | Variant is unknown
`QUuid::NCS` | `0` | Reserved for NCS (Network Computing System) backward compatibility
`QUuid::DCE` | `2` | Distributed Computing Environment, the scheme used by QUuid
`QUuid::Microsoft` | `6` | Reserved for Microsoft backward compatibility (GUID)
`QUuid::Reserved` | `7` | Reserved for future definition

### enum QUuid::Version

This enum defines the values used in the version field of the UUID. The version field is meaningful only if the value in the variant field is QUuid::DCE.

Constant | Value | Description
--- | --- | ---
`QUuid::VerUnknown` | `-1` | Version is unknown
`QUuid::Time` | `1` | Time-based, by using timestamp, clock sequence, and MAC network card address (if available) for the node sections
`QUuid::EmbeddedPOSIX` | `2` | DCE Security version, with embedded POSIX UUIDs
`QUuid::Name` | `Md5` | Name-based, by using values from a name for all sections
`QUuid::Md5` | `3` | Alias for Name
`QUuid::Random` | `4` | Random-based, by using random numbers for all sections
`QUuid::Sha1` | `5` | Name-based version that uses SHA-1 hashing
`QUuid::UnixEpoch` | `7` | [since 6.9] Time-based UUID using the number of milliseconds since the UNIX epoch

## Member Function Documentation

### `[constexpr noexcept]` QUuid::QUuid()

Creates the null UUID. toString() will output the null UUID as "{00000000-0000-0000-0000-000000000000}".

### `[explicit noexcept]` QUuid::QUuid(QAnyStringView text)

Creates a QUuid object from the string text, which must be formatted as five hex fields separated by '-', e.g., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex digit. The curly braces shown here are optional, but it is normal to include them. If the conversion fails, a null UUID is created. See toString() for an explanation of how the five hex fields map to the public data members in QUuid.

Note: In Qt versions prior to 6.3, this constructor was an overload set consisting of QString, QByteArray and `const char*` instead of one constructor taking QAnyStringView.

See also toString() and QUuid().

### `[constexpr noexcept]` QUuid::QUuid(const GUID &guid)

Casts a Windows guid to a Qt QUuid.

Warning: This function is only for Windows platforms.

### `[explicit noexcept, since 6.6]` QUuid::QUuid(QUuid::Id128Bytes id128, QSysInfo::Endian order = QSysInfo::BigEndian)

Creates a QUuid based on the integral id128 parameter. The input id128 parameter is considered to have byte order order.

This function was introduced in Qt 6.6.

See also fromBytes(), toBytes(), toRfc4122(), and toUInt128().

### `[constexpr noexcept]` QUuid::QUuid(uint l, ushort w1, ushort w2, uchar b1, uchar b2, uchar b3, uchar b4, uchar b5, uchar b6, uchar b7, uchar b8)

Creates a UUID with the value specified by the parameters, l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8.

Example:

     // {67C8770B-44F1-410A-AB9A-F9B5446F13EE}
     QUuid IID_MyInterface(0x67c8770b, 0x44f1, 0x410a, 0xab, 0x9a, 0xf9, 0xb5, 0x44, 0x6f, 0x13, 0xee);

### `[static]` QUuid QUuid::createUuid()

On any platform other than Windows, this function returns a new UUID with variant QUuid::DCE and version QUuid::Random. On Windows, a GUID is generated using the Windows API and will be of the type that the API decides to create.

See also variant() and version().

### `[static noexcept]` QUuid QUuid::createUuidV3(QUuid ns, QByteArrayView baseData)

This function returns a new UUID with variant QUuid::DCE and version QUuid::Md5. ns is the namespace and baseData is the basic data as described by RFC 4122.

Note: In Qt versions prior to 6.8, this function took QByteArray, not QByteArrayView.

See also variant(), version(), createUuidV5(), and createUuidV7().

### `[static]` QUuid QUuid::createUuidV3(const QUuid &ns, const QString &baseData)

This function returns a new UUID with variant QUuid::DCE and version QUuid::Md5. ns is the namespace and baseData is the basic data as described by RFC 4122.

See also variant(), version(), createUuidV5(), and createUuidV7().

### `[static noexcept]` QUuid QUuid::createUuidV5(QUuid ns, QByteArrayView baseData)

This function returns a new UUID with variant QUuid::DCE and version QUuid::Sha1. ns is the namespace and baseData is the basic data as described by RFC 4122.

Note: In Qt versions prior to 6.8, this function took QByteArray, not QByteArrayView.

See also variant(), version(), and createUuidV3().

### `[static]` QUuid QUuid::createUuidV5(const QUuid &ns, const QString &baseData)

This function returns a new UUID with variant QUuid::DCE and version QUuid::Sha1. ns is the namespace and baseData is the basic data as described by RFC 4122.

See also variant(), version(), and createUuidV3().

### `[static, since 6.9]` QUuid QUuid::createUuidV7()

This function returns a new UUID with variant QUuid::DCE and version QUuid::UnixEpoch.

It uses a time-ordered value field derived from the number of milliseconds since the UNIX Epoch as described by RFC9562.

This function was introduced in Qt 6.9.

See also variant(), version(), createUuidV3(), and createUuidV5().

### `[static, since 6.6]` QUuid QUuid::fromBytes(const void *bytes, QSysInfo::Endian order = QSysInfo::BigEndian)

Reads 128 bits (16 bytes) from bytes using byte order order and returns the QUuid corresponding to those bytes. This function does the same as fromRfc4122() if the byte order order is QSysInfo::BigEndian.

This function was introduced in Qt 6.6.

See also fromRfc4122().

### `[static]` QUuid QUuid::fromCFUUID(CFUUIDRef uuid)

Constructs a new QUuid containing a copy of the uuid CFUUID.

Note: this function is only available on Apple platforms.

### `[static]` QUuid QUuid::fromNSUUID(const NSUUID *uuid)

Constructs a new QUuid containing a copy of the uuid NSUUID.

Note: this function is only available on Apple platforms.

### `[static noexcept]` QUuid QUuid::fromRfc4122(QByteArrayView bytes)

Creates a QUuid object from the binary representation of the UUID, as specified by RFC 4122 section 4.1.2. See toRfc4122() for a further explanation of the order of bytes required.

The byte array accepted is NOT a human readable format.

If the conversion fails, a null UUID is created.

Note: In Qt versions prior to 6.3, this function took QByteArray, not QByteArrayView.

See also toRfc4122(), QUuid(), and fromBytes().

### `[static noexcept]` QUuid QUuid::fromString(QAnyStringView string)

Creates a QUuid object from the string string, which must be formatted as five hex fields separated by '-', e.g., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex digit. The curly braces shown here are optional, but it is normal to include them. If the conversion fails, a null UUID is returned. See toString() for an explanation of how the five hex fields map to the public data members in QUuid.

Note: In Qt versions prior to 6.3, this function was an overload set consisting of QStringView and QLatin1StringView instead of one function taking QAnyStringView.

See also toString() and QUuid().

### `[static constexpr noexcept, since 6.6]` QUuid QUuid::fromUInt128(quint128 uuid, QSysInfo::Endian order = QSysInfo::BigEndian)

Creates a QUuid based on the integral uuid parameter. The input uuid parameter is considered to have byte order order.

Note: This function is only present on platforms that offer a 128-bit integer type.

This function was introduced in Qt 6.6.

See also toUInt128(), fromBytes(), toBytes(), and toRfc4122().

### `[constexpr noexcept]` bool QUuid::isNull() const

Returns `true` if this is the null UUID {00000000-0000-0000-0000-000000000000}; otherwise returns `false`.

### QByteArray QUuid::toByteArray(QUuid::StringFormat mode = WithBraces) const

Returns the string representation of this QUuid, with the formattiong controlled by the mode parameter. From left to right, the five hex fields are obtained from the four public data members in QUuid as follows:

Field # | Source
--- | ---
1 | data1
2 | data2
3 | data3
4 | data4[0] .. data4[1]
5 | data4[2] .. data4[7]

### `[noexcept, since 6.6]` QUuid::Id128Bytes QUuid::toBytes(QSysInfo::Endian order = QSysInfo::BigEndian) const

Returns a 128-bit ID created from this QUuid on the byte order specified by order. The binary content of this function is the same as toRfc4122() if the order is QSysInfo::BigEndian. See that function for more details.

This function was introduced in Qt 6.6.

See also toRfc4122(), fromBytes(), and QUuid().

### CFUUIDRef QUuid::toCFUUID() const

Creates a CFUUID from a QUuid.

The caller owns the CFUUID and is responsible for releasing it.

Note: this function is only available on Apple platforms.

### NSUUID *QUuid::toNSUUID() const

Creates a NSUUID from a QUuid.

The NSUUID is autoreleased.

Note: this function is only available on Apple platforms.

### QByteArray QUuid::toRfc4122() const

Returns the binary representation of this QUuid. The byte array is in big endian format, and formatted according to RFC 4122, section 4.1.2 - "Layout and byte order".

The order is as follows:

Field # | Source
--- | ---
1 | data1
2 | data2
3 | data3
4 | data4[0] .. data4[7]

The bytes in the byte array returned by this function contains the same binary content as toBytes().

See also toBytes().

### QString QUuid::toString(QUuid::StringFormat mode = WithBraces) const

Returns the string representation of this QUuid, with the formattiong controlled by the mode parameter. From left to right, the five hex fields are obtained from the four public data members in QUuid as follows:

Field # | Source
--- | ---
1 | data1
2 | data2
3 | data3
4 | data4[0] .. data4[1]
5 | data4[2] .. data4[7]

### `[constexpr noexcept, since 6.6]` quint128 QUuid::toUInt128(QSysInfo::Endian order = QSysInfo::BigEndian) const

Returns a 128-bit integer created from this QUuid on the byte order specified by order. The binary content of this function is the same as toRfc4122() if the order is QSysInfo::BigEndian. See that function for more details.

Note: This function is only present on platforms that offer a 128-bit integer type.

This function was introduced in Qt 6.6.

See also toRfc4122(), fromUInt128(), toBytes(), fromBytes(), and QUuid().

### `[constexpr noexcept]` QUuid::Variant QUuid::variant() const

Returns the value in the variant field of the UUID. If the return value is QUuid::DCE, call version() to see which layout it uses. The null UUID is considered to be of an unknown variant.

See also version().

### `[constexpr noexcept]` QUuid::Version QUuid::version() const

Returns the version field of the UUID, if the UUID's variant field is QUuid::DCE. Otherwise it returns QUuid::VerUnknown.

See also variant().

### `[constexpr noexcept]` GUID QUuid::operator GUID() const

Returns a Windows GUID from a QUuid.

Warning: This function is only for Windows platforms.

### `[constexpr noexcept]` QUuid &QUuid::operator=(const GUID &guid)

Assigns a Windows guid to a Qt QUuid.

Warning: This function is only for Windows platforms.

## Related Non-Members

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

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

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

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

Performs a comparison of lhs against rhs and returns `true` if the relative sorting of lhs and rhs is correct for the operation in question, `false` otherwise. Note that the sorting performed by this functions may not be equal to the sorting of the strings created by toString(), nor the integers toId128(), or the byte array returned by toBytes() and toRfc4122().

See also variant().

### `[noexcept]` size_t qHash(const QUuid &key, size_t seed = 0)

Returns the hash value for key, using seed to seed the calculation.

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

Returns `true` if lhs UUID is not equal to the Windows GUID rhs; otherwise returns `false`.

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

Returns `true` if lhs QUuid and the rhs QUuid are different; otherwise returns `false`.

### QDataStream &operator<<(QDataStream &s, const QUuid &id)

Writes the UUID id to the data stream s.

### QDebug operator<<(QDebug dbg, const QUuid &id)

Writes the UUID id to the output stream for debugging information dbg.

### `[constexpr noexcept]` bool operator==(const QUuid &lhs, const GUID &rhs)

Returns `true` if lhs UUID is equal to the Windows GUID rhs; otherwise returns `false`.

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

Returns `true` if lhs QUuid and the rhs QUuid are identical; otherwise returns `false`.

### QDataStream &operator>>(QDataStream &s, QUuid &id)

Reads a UUID from the stream s into id.