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std::random_device(3) C++ Standard Libary std::random_device(3) NAME std::random_device - std::random_device Synopsis Defined in header <random> class random_device; (since C++11) std::random_device is a uniformly-distributed integer random number generator that produces non-deterministic random numbers. std::random_device may be implemented in terms of an implementation- defined pseudo-random number engine if a non-deterministic source (e.g. a hardware device) is not available to the implementation. In this case each std::ran- dom_device object may generate the same number sequence. Member types Member type Definition result_type unsigned int Member functions Construction constructor constructs the engine (C++11) (public member function) operator= the assignment operator is deleted (deleted) (public member function) Generation operator() advances the engine's state and returns the gener- ated value (C++11) (public member function) Characteristics obtains the entropy estimate for the non-determin- istic random entropy number generator (public member function) min gets the smallest possible value in the output range [static] (C++11) (public static member function) max gets the largest possible value in the output range [static] (C++11) (public static member function) Notes A notable implementation where std::random_device is deterministic is old versions of MinGW (bug 338, fixed since GCC 9.2). The latest MinGW versions can be downloaded from GCC with the MCF thread model. Example // Run this code #include <iostream> #include <string> #include <map> #include <random> int main() { std::random_device rd; std::map<int, int> hist; std::uniform_int_distribution<int> dist(0, 9); for (int n = 0; n < 20000; ++n) { ++hist[dist(rd)]; // note: demo only: the performance of many // implementations of random_device degrades sharply // once the entropy pool is exhausted. For practical use // random_device is generally only used to seed // a PRNG such as mt19937 } for (auto p : hist) { std::cout << p.first << " : " << std::string(p.second/100, '*') << '\n'; } } Possible output: 0 : ******************** 1 : ******************* 2 : ******************** 3 : ******************** 4 : ******************** 5 : ******************* 6 : ******************** 7 : ******************** 8 : ******************* 9 : ******************** http://cppreference.com 2022.07.31 std::random_device(3)
NAME | Synopsis | Member types | Member functions | Construction | Generation | Characteristics | Notes | Example | Possible output:
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