When do I use std::random_device?

Question

According to the standard, std::random_device works the following way:

result_type operator()();

Returns: A non-deterministic random value, uniformly distributed between min() and max(), inclusive. It is implementation-defined how these values are generated.

And there are a couple of ways you can use it. To seed an engine:

std::mt19937 eng(std::random_device{}());

As an engine in itself:

std::uniform_int_distribution<> uid(1, 10);
std::cout << dist(dev);

Because it is implementation-defined, it doesn't sound as strong as say std::seed_seq or srand(time(nullptr)). Do I prefer to use it as a seed, as an engine or not at all?

Answer 1

Generally speaking, std::random_device should be the source of the most truly random information you can access on your platform. That being said, accessing it is much slower than std::mt19937 or what not.

The correct behavior is to use std::random_device to seed something like std::mt19937.