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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