std::random_device::operator()
From cppreference.com
                    
                                        
                    < cpp | numeric | random | random device
                    
                                                            
                    | result_type operator()(); | (since C++11) | |
Generates a non-deterministic uniformly-distributed random value.
| Contents | 
[edit] Parameters
(none)
[edit] Return value
A random number uniformly distributed in [min(), max()].
[edit] Exceptions
Throws an implementation-defined exception derived from std::exception if a random number could not be generated.
[edit] See also
| [static] | gets the smallest possible value in the output range (public static member function) | 
| [static] | gets the largest possible value in the output range (public static member function) | 


