std::random_device::random_device

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< cpp | numeric | random | random device


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. Typical implementation on a Linux system, for example, expects token to be the name of a character device that produces random numbers when read from, with the default value "/dev/urandom".

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

[edit] Exceptions

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

[edit] 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 /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';
}

Output:

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

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)