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Returns a random value.

template<class Engine>
    result_type operator()(Engine& eng);
template<class Engine>
    result_type operator()(Engine& eng,
        const param_type& par0);

The type of the random engine.


The random engine.


The parameter package used as the source of the random value.

The first member function uses the engine eng as a source of uniformly distributed integral values and returns integral values with each value i occurring with probability pr(i) = e^-stored_mean * (stored_mean^i / i!).

The second member function behaves the same, except that it uses the parameters stored in par0.


// std_tr1__random__poisson_distribution_operator_fn.cpp 
// compile with: /EHsc 
#include <random> 
#include <iostream> 
typedef std::mt19937 Myeng; 
typedef std::poisson_distribution<int, double> Mydist; 
int main() 
    Myeng eng; 
    Mydist dist(3.5); 
    Mydist::input_type engval = eng(); 
    Mydist::result_type distval = dist(eng); 
    distval = distval;  // to quiet "unused" warnings 
    engval = engval; 
    std::cout << "mean == " << dist.mean() << std::endl; 
    dist.reset(); // discard any cached values 
    std::cout << "a random value == " << dist(eng) << std::endl; 
    std::cout << "a random value == " << dist(eng) << std::endl; 
    std::cout << "a random value == " << dist(eng) << std::endl; 
    return (0); 
mean == 3.5
a random value == 5
a random value == 2
a random value == 11

Header: <random>

Namespace: std

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