random_device Class
Generates a random sequence from an external device.
class random_device {
public:
typedef unsigned int result_type;
// cosntructor
explicit random_device(const std::string& token = "");
// properties
static result_type min();
static result_type max();
double entropy() const;
// generate
result_type operator()();
// no-copy functions
random_device(const random_device&) = delete;
void operator=(const random_device&) = delete;
};
Members
Remarks
The class describes a source of random numbers, and is allowed but not required to be non-deterministic or cryptographically secure by the ISO C++ Standard. In the Visual Studio implementation the values produced are non-deterministic and cryptographically secure, but runs more slowly than generators created from engines and engine adaptors (such as mersenne_twister_engine, the high quality and fast engine of choice for most applications).
random_device results are uniformly distributed in the closed range [0, 232).
random_device is not guaranteed to result in a non-blocking call.
Generally, random_device is used to seed other generators created with engines or engine adaptors. For more information, see <random>.
Example
The following code demonstrates basic functionality of this class and example results. Because of the non-deterministic nature of random_device, the random values shown in the Output section will not match your results. This is normal and expected.
// random_device_engine.cpp
// cl.exe /W4 /nologo /EHsc /MTd
#include <random>
#include <iostream>
using namespace std;
int main()
{
random_device gen;
cout << "entropy == " << gen.entropy() << endl;
cout << "min == " << gen.min() << endl;
cout << "max == " << gen.max() << endl;
cout << "a random value == " << gen() << endl;
cout << "a random value == " << gen() << endl;
cout << "a random value == " << gen() << endl;
}
Output:
entropy == 32 min == 0 max == 4294967295 10 random values: 4183829181 1454391608 1176278697 2468830096 3959347222 1803123400 1339590545 1304896877 604088490 2293276253
This example is simplistic and not representative of the general use-case for this generator. For a more representative code example, see <random>.
Requirements
Header: <random>
Namespace: std