QRandomGenerator Class

     quint32 value = QRandomGenerator::global()->generate();

     QRandomGenerator prng1(1234), prng2(1234);
     Q_ASSERT(prng1.generate() == prng2.generate());
     Q_ASSERT(prng1.generate64() == prng2.generate64());

     int x = QRandomGenerator::global()->generate();
     int y = QRandomGenerator::global()->generate();
     int w = QRandomGenerator::global()->bounded(16384);
     int h = QRandomGenerator::global()->bounded(16384);

     std::uniform_real_distribution dist(1, 2.5);
     return dist(*QRandomGenerator::global());

Member Function Documentation

QRandomGenerator::QRandomGenerator(const QRandomGenerator &other)

Creates a copy of the generator state in the other object. If other is QRandomGenerator::system() or a copy of that, this object will also read from the operating system random-generating facilities. In that case, the sequences generated by the two objects will be different.

In all other cases, the new QRandomGenerator object will start at the same position in the deterministic sequence as the other object was. Both objects will generate the same sequence from this point on.

For that reason, it is not advisable to create a copy of QRandomGenerator::global(). If one needs an exclusive deterministic generator, consider instead using securelySeeded() to obtain a new object that shares no relationship with the QRandomGenerator::global().

QRandomGenerator::QRandomGenerator(const quint32 *begin, const quint32 *end)

This is an overloaded function.

Initializes this QRandomGenerator object with the values found in the range from begin to end as the seed. Two objects constructed or reseeded with the same seed value will produce the same number sequence.

This constructor is equivalent to:

     std::seed_seq sseq(begin, end);
     QRandomGenerator generator(sseq);

See also seed() and securelySeeded().

QRandomGenerator::QRandomGenerator(std::seed_seq &sseq)

This is an overloaded function.

Initializes this QRandomGenerator object with the seed sequence sseq as the seed. Two objects constructed or reseeded with the same seed value will produce the same number sequence.

See also seed() and securelySeeded().

QRandomGenerator::QRandomGenerator(const quint32 *seedBuffer, qsizetype len)

This is an overloaded function.

Initializes this QRandomGenerator object with len values found in the array seedBuffer as the seed. Two objects constructed or reseeded with the same seed value will produce the same number sequence.

This constructor is equivalent to:

     std::seed_seq sseq(seedBuffer, seedBuffer + len);
     QRandomGenerator generator(sseq);

See also seed() and securelySeeded().

template <qsizetype N> QRandomGenerator::QRandomGenerator(const quint32 (&)[N] seedBuffer = N)

This is an overloaded function.

Initializes this QRandomGenerator object with the values found in the array seedBuffer as the seed. Two objects constructed or reseeded with the same seed value will produce the same number sequence.

See also seed() and securelySeeded().

QRandomGenerator::QRandomGenerator(quint32 seedValue = 1)

Initializes this QRandomGenerator object with the value seedValue as the seed. Two objects constructed or reseeded with the same seed value will produce the same number sequence.

See also seed() and securelySeeded().

double QRandomGenerator::bounded(double highest)

Generates one random double in the range between 0 (inclusive) and highest (exclusive). This function is equivalent to and is implemented as:

     return generateDouble() * highest;

If the highest parameter is negative, the result will be negative too; if it is infinite or NaN, the result will be infinite or NaN too (that is, not random).

See also generateDouble() and bounded().

quint32 QRandomGenerator::bounded(quint32 highest)

This is an overloaded function.

Generates one random 32-bit quantity in the range between 0 (inclusive) and highest (exclusive). The same result may also be obtained by using std::uniform_int_distribution with parameters 0 and highest - 1. That class can also be used to obtain quantities larger than 32 bits.

For example, to obtain a value between 0 and 255 (inclusive), one would write:

     quint32 v = QRandomGenerator::global()->bounded(256);

Naturally, the same could also be obtained by masking the result of generate() to only the lower 8 bits. Either solution is as efficient.

Note that this function cannot be used to obtain values in the full 32-bit range of quint32. Instead, use generate().

See also generate(), generate64(), and generateDouble().

quint32 QRandomGenerator::bounded(quint32 lowest, quint32 highest)

This is an overloaded function.

Generates one random 32-bit quantity in the range between lowest (inclusive) and highest (exclusive). The highest parameter must be greater than lowest.

The same result may also be obtained by using std::uniform_int_distribution with parameters lowest and \a highest - 1. That class can also be used to obtain quantities larger than 32 bits.

For example, to obtain a value between 1000 (incl.) and 2000 (excl.), one would write:

     quint32 v = QRandomGenerator::global()->bounded(1000, 2000);

Note that this function cannot be used to obtain values in the full 32-bit range of quint32. Instead, use generate().

See also generate(), generate64(), and generateDouble().

int QRandomGenerator::bounded(int highest)

This is an overloaded function.

Generates one random 32-bit quantity in the range between 0 (inclusive) and highest (exclusive). highest must be positive.

Note that this function cannot be used to obtain values in the full 32-bit range of int. Instead, use generate() and cast to int.

See also generate(), generate64(), and generateDouble().

int QRandomGenerator::bounded(int lowest, int highest)

This is an overloaded function.

Generates one random 32-bit quantity in the range between lowest (inclusive) and highest (exclusive), both of which may be negative, but highest must be greater than lowest.

Note that this function cannot be used to obtain values in the full 32-bit range of int. Instead, use generate() and cast to int.

See also generate(), generate64(), and generateDouble().

void QRandomGenerator::discard(unsigned long long z)

Discards the next z entries from the sequence. This method is equivalent to calling generate() z times and discarding the result, as in:

     while (z--)
         generator.generate();

template <typename UInt, IfValidUInt<UInt>> void QRandomGenerator::fillRange(UInt *buffer, qsizetype count)

Generates count 32- or 64-bit quantities (depending on the type UInt) and stores them in the buffer pointed by buffer. This is the most efficient way to obtain more than one quantity at a time, as it reduces the number of calls into the Random Number Generator source.

For example, to fill a vector of 16 entries with random values, one may write:

     QVector<quint32> vector;
     vector.resize(16);
     QRandomGenerator::global()->fillRange(vector.data(), vector.size());

See also generate().

template <typename UInt, int N, IfValidUInt<UInt>> void QRandomGenerator::fillRange(UInt (&)[N] buffer = N)

Generates N 32- or 64-bit quantities (depending on the type UInt) and stores them in the buffer array. This is the most efficient way to obtain more than one quantity at a time, as it reduces the number of calls into the Random Number Generator source.

For example, to fill generate two 32-bit quantities, one may write:

     quint32 array[2];
     QRandomGenerator::global()->fillRange(array);

It would have also been possible to make one call to generate64() and then split the two halves of the 64-bit value.

See also generate().

quint64 QRandomGenerator::generate64()

Generates a 64-bit random quantity and returns it.

See also operator()() and generate().

quint32 QRandomGenerator::generate()

Generates a 32-bit random quantity and returns it.

See also operator()() and generate64().

template <typename ForwardIterator> void QRandomGenerator::generate(ForwardIterator begin, ForwardIterator end)

Generates 32-bit quantities and stores them in the range between begin and end. This function is equivalent to (and is implemented as):

     std::generate(begin, end, [this]() { return generate(); });

This function complies with the requirements for the function std::seed_seq::generate, which requires unsigned 32-bit integer values.

Note that if the [begin, end) range refers to an area that can store more than 32 bits per element, the elements will still be initialized with only 32 bits of data. Any other bits will be zero. To fill the range with 64 bit quantities, one can write:

     std::generate(begin, end, []() { return QRandomGenerator::global()->generate64(); });

If the range refers to contiguous memory (such as an array or the data from a QVector), the fillRange() function may be used too.

See also fillRange().

double QRandomGenerator::generateDouble()

Generates one random qreal in the canonical range [0, 1) (that is, inclusive of zero and exclusive of 1).

This function is equivalent to:

     QRandomGenerator64 rd;
     return std::generate_canonical<qreal, std::numeric_limits<qreal>::digits>(rd);

The same may also be obtained by using std::uniform_real_distribution with parameters 0 and 1.

See also generate(), generate64(), and bounded().

[static] QRandomGenerator *QRandomGenerator::global()

Returns a pointer to a shared QRandomGenerator that was seeded using securelySeeded(). This function should be used to create random data without the expensive creation of a securely-seeded QRandomGenerator for a specific use or storing the rather large QRandomGenerator object.

For example, the following creates a random RGB color:

     return QColor::fromRgb(QRandomGenerator::global()->generate());

Accesses to this object are thread-safe and it may therefore be used in any thread without locks. The object may also be copied and the sequence produced by the copy will be the same as the shared object will produce. Note, however, that if there are other threads accessing the global object, those threads may obtain samples at unpredictable intervals.

Note: This function is thread-safe.

See also securelySeeded() and system().

[static] result_type QRandomGenerator::max()

Returns the maximum value that QRandomGenerator may ever generate. That is, std::numeric_limits<result_type>::max().

See also min() and QRandomGenerator64::max().

[static] result_type QRandomGenerator::min()

Returns the minimum value that QRandomGenerator may ever generate. That is, 0.

See also max() and QRandomGenerator64::min().

[static] QRandomGenerator QRandomGenerator::securelySeeded()

Returns a new QRandomGenerator object that was securely seeded with QRandomGenerator::system(). This function will obtain the ideal seed size for the algorithm that QRandomGenerator uses and is therefore the recommended way for creating a new QRandomGenerator object that will be kept for some time.

Given the amount of data required to securely seed the deterministic engine, this function is somewhat expensive and should not be used for short-term uses of QRandomGenerator (using it to generate fewer than 2600 bytes of random data is effectively a waste of resources). If the use doesn't require that much data, consider using QRandomGenerator::global() and not storing a QRandomGenerator object instead.

See also global() and system().

void QRandomGenerator::seed(quint32 seed = 1)

Reseeds this object using the value seed as the seed.

void QRandomGenerator::seed(std::seed_seq &seed)

This is an overloaded function.

Reseeds this object using the seed sequence seed as the seed.

[static] QRandomGenerator *QRandomGenerator::system()

Returns a pointer to a shared QRandomGenerator that always uses the facilities provided by the operating system to generate random numbers. The system facilities are considered to be cryptographically safe on at least the following operating systems: Apple OSes (Darwin), BSDs, Linux, Windows. That may also be the case on other operating systems.

They are also possibly backed by a true hardware random number generator. For that reason, the QRandomGenerator returned by this function should not be used for bulk data generation. Instead, use it to seed QRandomGenerator or a random engine from the <random> header.

The object returned by this function is thread-safe and may be used in any thread without locks. It may also be copied and the resulting QRandomGenerator will also access the operating system facilities, but they will not generate the same sequence.

Note: This function is thread-safe.

See also securelySeeded() and global().

result_type QRandomGenerator::operator()()

Generates a 32-bit random quantity and returns it.

See also generate() and generate64().