senkora on C++ Seeding Surprises (2015)

Comment on C++ Seeding Surprises (2015)parent

Why not just run your tests with a fixed seed? e.g.

    std::mt19937 gen(42);
    std::uniform_int_distribution<> dist(1, 100);
    int random_number = dist(gen);

jhasse 1y

uniform_int_distribution differs between compilers/platforms! Don't use it if you don't want true randomness.

senkora 1y

Thank you, that makes sense. I can see that being an issue for testing.

I wouldn't describe "pseudo-random sequences that differ between compilers/platforms/versions but are deterministic for a given toolchain" as "true randomness" but I understand the point.

I have confirmed that uniform_int_distribution gives different results on x86-64 clang (trunk) with libc++ [1] vs x86-64 clang (trunk) with libstdc++ [2].

[1]: https://godbolt.org/z/dd5YMs7zo

[2]: https://godbolt.org/z/8svGn7Exc

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