| Common mathematical functions | |||||||||||||||||||||||||||||||
| Mathematical special functions(C++17) | |||||||||||||||||||||||||||||||
| Mathematical constants(C++20) | |||||||||||||||||||||||||||||||
| Basic linear algebra algorithms(C++26) | |||||||||||||||||||||||||||||||
| Data-parallel types (SIMD)(C++26) | |||||||||||||||||||||||||||||||
| Floating-point environment(C++11) | |||||||||||||||||||||||||||||||
| Complex numbers | |||||||||||||||||||||||||||||||
Numeric array (valarray) | |||||||||||||||||||||||||||||||
| Pseudo-random number generation | |||||||||||||||||||||||||||||||
| Bit manipulation(C++20) | |||||||||||||||||||||||||||||||
| Saturation arithmetic(C++26) | |||||||||||||||||||||||||||||||
| Factor operations | |||||||||||||||||||||||||||||||
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| Interpolations | |||||||||||||||||||||||||||||||
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| Generic numeric operations | |||||||||||||||||||||||||||||||
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| C-style checked integer arithmetic | |||||||||||||||||||||||||||||||
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| Member functions | ||||
| Generation | ||||
| Characteristics | ||||
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 eachstd::random_device object may generate the same number sequence.
Contents |
| Member type | Definition |
result_type(C++11) | unsignedint |
Construction | |
| constructs the engine (public member function)[edit] | |
operator= (deleted)(C++11) | the assignment operator is deleted (public member function) |
Generation | |
| advances the engine's state and returns the generated value (public member function)[edit] | |
Characteristics | |
(C++11) | obtains the entropy estimate for the non-deterministic random number generator (public member function)[edit] |
[static] | gets the smallest possible value in the output range (public static member function)[edit] |
[static] | gets the largest possible value in the output range (public static member function)[edit] |
A notable implementation wherestd::random_device is deterministic in old versions of MinGW-w64 (bug 338, fixed since GCC 9.2). The latest MinGW-w64 versions can be downloaded fromGCC with the MCF thread model.
#include <iostream>#include <map>#include <random>#include <string> 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[x, y]: hist)std::cout<< x<<" : "<<std::string(y/100,'*')<<'\n';}
Possible output:
0 : ********************1 : *******************2 : ********************3 : ********************4 : ********************5 : *******************6 : ********************7 : ********************8 : *******************9 : ********************
