Contents

• Public Types
• Public Functions
• Static Public Members
• Related Non-Members
• Detailed Description

Detailed Description

TheQUuid class stores a Universally Unique Identifier (UUID).

UsingUniversallyUniqueIDentifiers (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,GloballyUniqueIDentifiers, but it refers to the same thing.

Actually, the GUID is onevariant of UUID. Multiple variants are in use. Each UUID contains a bit field that specifies which type (variant) of UUID it is. Callvariant() to discover which type of UUID an instance ofQUuid contains. It extracts the three most signifcant bits of byte 8 of the 16 bytes. InQUuid, byte 8 isQUuid::data4[0]. If you create instances ofQUuid using the constructor that accepts all the numeric values as parameters, use the following table to set the three most significant bits of parameterb1, which becomesQUuid::data4[0] and contains the variant field in its three most significant bits. In the table, 'x' meansdon't care.

Ifvariant() returnsQUuid::DCE, the UUID also contains aversion field in the four most significant bits ofQUuid::data3, and you can callversion() to discover which version yourQUuid contains. If you create instances ofQUuid using the constructor that accepts all the numeric values as parameters, use the following table to set the four most significant bits of parameterw2, which becomesQUuid::data3 and contains the version field in its four most significant bits.

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

Most platforms provide a tool for generating new UUIDs, e.g.uuidgen andguidgen. You can also usecreateUuid(). UUIDs generated bycreateUuid() are of the random type. TheirQUuid::Version bits are set toQUuid::Random, and theirQUuid::Variant bits are set toQUuid::DCE. The rest of the UUID is composed of random numbers. Theoretically, this means there is a small chance that a UUID generated bycreateUuid() will not be unique. But it isavery small chance.

UUIDs can be constructed from numeric values or from strings, or using the staticcreateUuid() function. They can be converted to a string withtoString(). UUIDs have avariant() and aversion(), and null UUIDs return true fromisNull().

Member Type Documentation

enum QUuid::Variant

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

enum QUuid::Version

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

Member Function Documentation

QUuid::QUuid()

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

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)

QUuid::QUuid(constQString & text)

Creates aQUuid object from the stringtext, which must be formatted as five hex fields separated by '-', e.g., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where '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. SeetoString() for an explanation of how the five hex fields map to the public data members inQUuid.

See alsotoString() andQUuid().

QUuid::QUuid(constQByteArray & text)

Creates aQUuid object from theQByteArraytext, which must be formatted as five hex fields separated by '-', e.g., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where '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. SeetoByteArray() for an explanation of how the five hex fields map to the public data members inQUuid.

This function was introduced in Qt 4.8.

See alsotoByteArray() andQUuid().

QUuid::QUuid(constGUID & guid)

Casts a Windowsguid to a QtQUuid.

Warning: This function is only for Windows platforms.

[static]QUuid QUuid::createUuid()

On any platform other than Windows, this function returns a new UUID with variantQUuid::DCE and versionQUuid::Random. If the /dev/urandom device exists, then the numbers used to construct the UUID will be of cryptographic quality, which will make the UUID unique. Otherwise, the numbers of the UUID will be obtained from the local pseudo-random number generator (qrand(), which is seeded byqsrand()) which is usually not of cryptograhic quality, which means that the UUID can't be guaranteed to be unique.

On a Windows platform, a GUID is generated, which almost certainlywill be unique, on this or any other system, networked or not.

See alsovariant() andversion().

[static]QUuid QUuid::fromRfc4122(constQByteArray & bytes)

Creates aQUuid object from the binary representation of the UUID given bybytes, as specified by RFC 4122 section 4.1.2. SeetoRfc4122() for a further explanation of the order of bytes required.

The byte array accepted isnot a human readable format.

If the conversion fails, a null UUID is created.

This function was introduced in Qt 4.8.

See alsotoRfc4122() andQUuid().

bool QUuid::isNull() const

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

QByteArray QUuid::toByteArray() const

Returns the binary representation of thisQUuid. The byte array is formatted as five hex fields separated by '-' and enclosed in curly braces, i.e., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' is a hex digit. From left to right, the five hex fields are obtained from the four public data members inQUuid as follows:

This function was introduced in Qt 4.8.

QByteArray QUuid::toRfc4122() const

Returns the binary representation of thisQUuid. 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:

This function was introduced in Qt 4.8.

QString QUuid::toString() const

Returns the string representation of thisQUuid. The string is formatted as five hex fields separated by '-' and enclosed in curly braces, i.e., "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' is a hex digit. From left to right, the five hex fields are obtained from the four public data members inQUuid as follows:

QUuid::Variant QUuid::variant() const

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

See alsoversion().

QUuid::Version QUuid::version() const

Returns theversion field of the UUID, if the UUID'svariant field isQUuid::DCE. Otherwise it returnsQUuid::VerUnknown.

See alsovariant().

QUuid::operator GUID() const

Returns a Windows GUID from aQUuid.

Warning: This function is only for Windows platforms.

QUuid::operator QString() const

Returns the string representation of the uuid.

See alsotoString().

bool QUuid::operator!=(constQUuid & other) const

Returns true if thisQUuid and theotherQUuid are different; otherwise returns false.

bool QUuid::operator!=(constGUID & guid) const

Returns true if this UUID is not equal to the Windows GUIDguid; otherwise returns false.

bool QUuid::operator<(constQUuid & other) const

Returns true if thisQUuid has the samevariant field as theotherQUuid and is lexicographicallybefore theotherQUuid. If theotherQUuid has a different variant field, the return value is determined by comparing the twovariants.

See alsovariant().

QUuid & QUuid::operator=(constGUID & guid)

Assigns a Windowsguid to a QtQUuid.

Warning: This function is only for Windows platforms.

bool QUuid::operator==(constQUuid & other) const

Returns true if thisQUuid and theotherQUuid are identical; otherwise returns false.

bool QUuid::operator==(constGUID & guid) const

Returns true if this UUID is equal to the Windows GUIDguid; otherwise returns false.

bool QUuid::operator>(constQUuid & other) const

Returns true if thisQUuid has the samevariant field as theotherQUuid and is lexicographicallyafter theotherQUuid. If theotherQUuid has a different variant field, the return value is determined by comparing the twovariants.

See alsovariant().

Related Non-Members

QDataStream &operator<<(QDataStream & s, constQUuid & id)

Writes the UUIDid to the data streams.

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

Reads a UUID from the streams intoid.