std::discrete_distribution<IntType>::probabilities

#include <iostream>
#include <vector>
#include <random>
int main()
{
    std::discrete_distribution<> d({40, 10, 10, 40});
    std::vector<double> p = d.probabilities();
    for(auto n : p)
        std::cout << n << ' ';
    std::cout << '\n';
}