std::random_device:: operator()

From cppreference.com
result_type operator ( ) ( ) ;
(since C++11)

Generates a non-deterministic uniformly-distributed random value.

Parameters

(none)

Return value

A random number uniformly distributed in [ min ( ) , max ( ) ].

Exceptions

Throws an implementation-defined exception derived from std::exception if a random number could not be generated.

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)