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Showing content from https://cplusplus.com/reference/random/discrete_distribution/discrete_distribution/ below:

public member function

<random>

discrete_distribution();

template <class InputIterator>  discrete_distribution (InputIterator first, InputIterator last);

discrete_distribution (initializer_list<double> il);

template <class UnaryOperation>  discrete_distribution (size_t nw, double xmin, double xmax, UnaryOperation fw);

 explicit discrete_distribution (const param_type& parm);

Construct discrete distribution

(1) default constructor

The distribution will always produce zero.

(2) range constructor

The sequence of values in the range is used as the weights for each integer value from 0 to (n-1), where n is the distance between the iterators.

(3) initializer list

The sequence in the list is used as the weights for each integer value from 0 to (n-1), where n is the size of the initializer list.

(4) operation constructor

Each integer value k in the closed range between 0 and (nw-1) is given the weight resulting from calling:

1

fw(xmin+(xmax-xmin)*(k+0.5)/nw)

(5) param constructor

The distribution adopts the distribution parameters specified by parm.

All weights shall be non-negative values, and at least one of the values in the sequence must be positive.

first, last

Input iterators to the initial and final positions in a range. The range used is [first,last), which includes all the elements between first and last, including the element pointed by first but not the element pointed by last.
If first==last, the distribution will always produce zero.
The function template type shall be an input iterator that points to some type convertible to double.

il

An initializer_list object.
These objects are automatically constructed from initializer list declarators.

nw

Number of weights: The highest possible number produced by the distribution is (nw-1).

xmin,xmax

Bounds of a range of values to be passed to fw. The first value passed to fw is (xmin+(xmax-xmin)/2*n), and then, nw values are passed with increases of ((xmax-xmin)/2).

fw

A pointer to a function or a function object that can take a single argument of a type convertible from double and return a value convertible to double.

parm

An object representing the distribution's parameters, obtained by a call to member function param.
param_type is a member type.

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// discrete_distribution constructor
#include <iostream>
#include <chrono>
#include <random>
#include <functional>
#include <array>

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);

  std::array<double,4> init = {1.0,2.0,3.0,4.0};

  std::discrete_distribution<int> first;
  std::discrete_distribution<int> second (init.begin(),init.end());
  std::discrete_distribution<int> third {0.1,0.2,0.3,0.4};
  std::discrete_distribution<int> fourth (4,0.0,40.0,std::bind2nd(std::plus<double>(),5.0));
  std::discrete_distribution<int> fifth (fourth.param());

  // display probabilities:
  std::cout << "displaying probabilities:";
  std::cout << std::endl << "first : ";
  for (double x:first.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "second: ";
  for (double x:second.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "third : ";
  for (double x:third.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "fourth: ";
  for (double x:fourth.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "fifth : ";
  for (double x:fifth.probabilities()) std::cout << x << " ";
  std::cout << std::endl;

  return 0;
}

displaying probabilities:
first : 1
second: 0.1 0.2 0.3 0.4
third : 0.1 0.2 0.3 0.4
fourth: 0.1 0.2 0.3 0.4
fifth : 0.1 0.2 0.3 0.4

discrete_distribution::reset

Reset distribution (public member function)

discrete_distribution::param

Distribution parameters (public member function)

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