The C++ <random> Lame List

Network programmers of a certain age may remember the Windows Sockets Lame List.

I previously wrote a short “don’t-do-that-do-this” guide for modern C++ randomness, and I was recently reading another Reddit exchange featuring STL, author of many parts of Microsoft’s STL implementation, when it struck me that use of C++ <random> needs its own lame list to discourage using the old and busted C parts and encourage the using the new C++ hotness. So here, in no particular order, and with apologies to Keith Moore (wherever he may be) is an incomplete lame list for use of <random>.

1. Calling rand() or srand(). Lame.
2. Using time(NULL) to seed an RNG. Inexcusably lame.
3. Claiming, “But rand() is good enough for simple uses!” Dog lame.
4. Using random_shuffle() to permute a container. Mired in a sweaty mass of lameness.
5. Using default_random_engine. Nauseatingly lame.
6. Using % to get a random value in a range. Lame. Lame. Lame. Lame. Lame.
7. Not using random_device to seed an RNG. Violently lame.
8. Assuming that random_device is going to do the right thing on your platform. Uncontrollably lame.
9. Failing to handle a possible exception from the construction or use of random_device. Totally lame.
10. Using anything in the standard but mt19937 or mt19937_64 as a generator. Intensely lame.
11. Putting mt19937 on the stack. In all my years of observing lameness, I have seldom seen something this lame.
12. Seeding mt19937 with only one 32-bit word rather than its full state_size. Pushing the lameness envelope.
13. Forgetting that uniform_int_distribution works on a closed interval. Thrashing in a sea of lameness.
14. Passing random_device or a generator to generate_n() by value, forgetting to wrap it with ref(). Glaringly lame.
15. Failing to use seed_seq to initialize a generator’s state properly. Indescribably lame.
16. Not considering thread safety when using a generator. Floundering in an endless desert of lameness.
17. Using a global generator without making it thread_local. Suffocating in self lameness.
18. Using RAND_MAX instead of mt19937::max(). Perilously teetering on the edge of a vast chasm of lameness.

This list will undoubtedly grow as I continue to write lame code…