About random_device

[xx1182]

I'm starting to use the new c++11 library.
And i can't understand this function.
It says it will get a number from a random device.

And if it is not present will be a pseudoRNG.

How can i use it correctly?

Does usb-clocks exsist? If yes, where i can buy them and implementt it in random_device?

[Jakee]

A random_device is a true random number generator that does not process pseudo-random numbers. It is part of the random header.

#include <random>
random_device randomNum;

cout << (randomNum % 5) +1 << endl;//This will produce a random number between 1 and 5

Thats how you would use it, I dont know about "usb-clocks".

[xx1182]

Really? It is not that random?
It produces always the same number.

[Disch]

Jakee forgot the parenthesis:

cout << (randomNum() % 5) + 1 << endl;

Though with C++11 generators you typically would want to use a distribution instead of the % operator:

#include <random>
#include <iostream>
using namespace std;

int main()
{
    random_device gen;                          // the engine
    uniform_int_distribution<int>   dist(1,6);  // distribution (between 1-6 inclusive .. like a die roll)

    cout << dist(gen) << endl;      // <- generate a number
}

[xx1182]

I'm trying with this code

    random_device rd;
    uniform_int_distribution<int>   dist(1,6);
    cout << dist(rd) << endl;

It generates always the same number.

[xx1182]

Oh, i'm using MinGw as a compiler.

[Chervil]

http://www.cplusplus.com/reference/random/random_device/entropy/

"If the library implementation employs a random number engine instead of a real-random number generator, the value returned by this function is always zero."

[xx1182]

Ooo, that's why!
Do you know, some implementation rather than visual studio(resource eater IDE)?