public member function
<random>

std::exponential_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 exponential_distribution object transforms the values obtained this way so that successive calls to this member function with the same arguments produce floating-point values that follow an exponential distribution with the appropriate lambda parameter.

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, 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 (RealType).

Example

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// exponential_distribution example
#include <iostream>
#include <chrono>
#include <thread>
#include <random>

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

  std::exponential_distribution<double> distribution (1.0);

  std::cout << "ten beeps, spread by 1 second, on average: " << std::endl;
  for (int i=0; i<10; ++i) {
    double number = distribution(generator);
    std::chrono::duration<double> period ( number );
    std::this_thread::sleep_for( period );
    std::cout << "beep!" << std::endl;
  }

  return 0;
}


Output:
ten beeps, spread by 1 second, on average:
beep!
beep!
beep!
beep!
beep!
beep!
beep!
beep!
beep!
beep!

Complexity

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

See also