std::random_device::random_device

 

C++

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random_device (C++11)

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C library

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std::random_device

Member functions

random_device::random_device

Generation

random_device::operator()

Characteristics

random_device::entropy

random_device::min

random_device::max

 

explicit random_device(const std::string& token = /*implementation-defined*/ );	(1)	(since C++11)
random_device(const random_device& ) = delete;	(2)	(since C++11)

1) Constructs a new std::random_device object, making use of the argument token, if provided, in implementation-defined manner.

2) The copy constructor is deleted: std::random_device is not copyable.

Exceptions

Throws an implementation-defined exceptions derived from std::exception on failure.

Notes

The implementations in libc++ and libstdc++ expect token to be the name of a character device that produces random numbers when read from, with the default value "/dev/urandom", although where the CPU command RDRND is available, libstdc++ uses that as the default.

Example

Demonstrates the two commonly available types of std::random_device on Linux

Run this code

#include <iostream>
#include <random>
 
int main()
{
 
    std::uniform_int_distribution<int> d(0, 10);
 
    std::random_device rd1; // uses RDRND or /dev/urandom
    for(int n = 0; n < 10; ++n)
        std::cout << d(rd1) << ' ';
    std::cout << '\n';
 
    std::random_device rd2("/dev/random"); // much slower on Linux
    for(int n = 0; n < 10; ++n)
        std::cout << d(rd2) << ' ';
    std::cout << '\n';
}

Possible output:

7 10 7 0 4 4 6 9 4 7 
2 4 10 6 3 2 0 6 3 7