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::random_device
object may generate the same number sequence.
Member types
Member type | Definition |
---|---|
result_type | unsigned int |
Member functions
Construction | |
constructs the engine (public member function) | |
operator= (deleted) | the assignment operator is deleted (public member function) |
Generation | |
operator()
| advances the engine's state and returns the generated value (public member function) |
Characteristics | |
obtains the entropy estimate for the non-deterministic random number generator (public member function) | |
[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) |
Example
#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 : ********************
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