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.
#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
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