This header introduces random number generation facilities.
This library allows to produce random numbers using combinations of generators and distributions:
Generators: Objects that generate uniformly distributed numbers.
Distributions: Objects that transform sequences of numbers generated by a generator into sequences of numbers that follow a specific random variable distribution, such as uniform, Normal or Binomial.
Distribution objects generate random numbers by means of their operator() member, which takes a generator object as argument:
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std::default_random_engine generator;
std::uniform_int_distribution<int> distribution(1,6);
int dice_roll = distribution(generator); // generates number in the range 1..6
For repeated uses, both can be bound together:
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auto dice = std::bind ( distribution, generator );
int wisdom = dice()+dice()+dice();
Except for random_device, all standard generators defined in the library are random number engines, which are a kind of generators that use a particular algorithm to generate series of pseudo-random numbers. These algorithms need a seed as a source of randomness, and this seed can either be a single value or an object with a very specific generate() member function (see seed_seq for more info). A typical source of randomness for trivial tasks is time, such as the information provided by time or system_clock::now (for a typical example, see uniform_int_distribution::operator()).
As an alternative, trivial random numbers can also be generated using cstdlib's functions rand and srand.
Generators
Pseudo-random number engines (templates)
Generators that use an algorithm to generate pseudo-random numbers based on an initial seed: