public member function
<random>

std::discrete_distribution::operator()

(1)
template<class URNG>
result_type operator()(URNG& g);
(2)
template<class URNG>
result_type operator()(URNG& g, const param_type& parm);
Generate random number
Returns a new random number that follows the distribution's parameters associated to the object (version 1) or those specified by parm (version 2).

The generator object (g) supplies uniformly-distributed random integers through its operator() member function. The discrete_distribution object transforms the values obtained this way so that successive calls to this member function with the same arguments produce values that follow a discrete distribution with the appropriate weights for its possible values.

Parameters

g
A uniform random number generator object, used as the source of randomness.
URNG shall be a uniform random number generator type, such as one of the standard generator classes.
parm
An object representing the distribution's parameters (weights), obtained by a call to member function param.
param_type is a member type.

Return value

A new random number.
result_type is a member type, defined as an alias of the first class template parameter (IntType).

Example

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// discrete_distribution example
#include <iostream>
#include <chrono>
#include <random>

int main()
{
  // construct a trivial random generator engine from a time-based seed:
  unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
  std::default_random_engine generator (seed);

  // in a regular die, every number is equally likely:
  std::uniform_int_distribution<int> regular_die (1,6);

  // in this loaded die, the 6 is three times more likely:
  std::discrete_distribution<int> loaded_die {0,1,1,1,1,1,3};

  int regular_score = 0;
  int loaded_score = 0;

  for (int i=0; i<1000; ++i) {
    int regular_roll = regular_die(generator);
    int loaded_roll = loaded_die(generator);
    if (regular_roll<loaded_roll) ++loaded_score;
    else if (regular_roll>loaded_roll) ++regular_score;
  }

  std::cout << "after 1000 experiments:" << std::endl;
  std::cout << "regular die won: " << regular_score << " times." << std::endl;
  std::cout << "loaded die won: " << loaded_score << " times." << std::endl;
  std::cout << "ties: " << (1000-regular_score-loaded_score) << std::endl;

  return 0;
}


Possible output:
after 1000 experiments:
regular die won: 299 times.
loaded die won: 540 times.
ties: 161

Complexity

Amortized constant (a constant number of invocations of g.operator()).

See also

discrete_distribution::param
Distribution parameters (public member function)

C++