Qt 4.7: QUuid Class Reference

Qt Reference Documentation

# QUuid Class Reference

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

     #include <QUuid>

Note: All functions in this class are reentrant.

- List of all members, including inherited members

## Public Types

enum | Variant { VarUnknown, NCS, DCE, Microsoft, Reserved }
enum | Version { VerUnknown, Time, EmbeddedPOSIX, Name, Random }

## Public Functions

| QUuid ()
| QUuid ( uint l, ushort w1, ushort w2, uchar b1, uchar b2, uchar b3, uchar b4, uchar b5, uchar b6, uchar b7, uchar b8 )
| QUuid ( const QString & text )
| QUuid ( const GUID & guid )
bool | isNull () const
QString | toString () const
QUuid::Variant | variant () const
QUuid::Version | version () const
| operator GUID () const
| operator QString () const
bool | operator!= ( const QUuid & other ) const
bool | operator!= ( const GUID & guid ) const
bool | operator< ( const QUuid & other ) const
QUuid & | operator= ( const GUID & guid )
bool | operator== ( const QUuid & other ) const
bool | operator== ( const GUID & guid ) const
bool | operator> ( const QUuid & other ) const

## Static Public Members

QUuid | createUuid ()

## Related Non-Members

QDataStream & | operator<< ( QDataStream & s, const QUuid & id )
QDataStream & | operator>> ( QDataStream & s, QUuid & id )

## Detailed Description

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

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 signifcant 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 | Name
0 | 1 | 0 | 0 | Random

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::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` | `3` | Name-based, by using values from a name for all sections
`QUuid::Random` | `4` | Random-based, by using random numbers for all sections

## 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 ( const QString & 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 '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.

See also toString() and QUuid().

### QUuid::QUuid ( const GUID & guid )

Casts a Windows guid to a Qt QUuid.

Warning: This function is only for Windows platforms.

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

On any platform other than Windows, this function returns a new UUID with variant QUuid::DCE and version QUuid::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 by qsrand()) 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 certainly will be unique, on this or any other system, networked or not.

See also variant() and version().

### bool QUuid::isNull () const

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

### QString QUuid::toString () const

Returns the string representation of this QUuid. 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 in QUuid as follows:

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

### 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().

### 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().

### QUuid::operator GUID () const

Returns a Windows GUID from a QUuid.

Warning: This function is only for Windows platforms.

### QUuid::operator QString () const

Returns the string representation of the uuid.

See also toString().

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

Returns true if this QUuid and the other QUuid are different; otherwise returns false.

### bool QUuid::operator!= ( const GUID & guid ) const

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

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

Returns true if this QUuid has the same variant field as the other QUuid and is lexicographically before the other QUuid. If the other QUuid has a different variant field, the return value is determined by comparing the two variants.

See also variant().

### QUuid & QUuid::operator= ( const GUID & guid )

Assigns a Windows guid to a Qt QUuid.

Warning: This function is only for Windows platforms.

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

Returns true if this QUuid and the other QUuid are identical; otherwise returns false.

### bool QUuid::operator== ( const GUID & guid ) const

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

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

Returns true if this QUuid has the same variant field as the other QUuid and is lexicographically after the other QUuid. If the other QUuid has a different variant field, the return value is determined by comparing the two variants.

See also variant().

## Related Non-Members

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

Writes the UUID id to the data stream s.

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

Reads a UUID from the stream s into id.