Random number generation - merging bot articles by ProfessionalMenace · Pull Request #79 · TCCPP/wiki

ProfessionalMenace · 2026-02-21T21:40:34Z

migrated bot article
expanded content

jeremy-rifkin

Thanks for taking the time to write this! I have given it a quick look and left some comments below.

This is a very in-depth article on random number generators. If this is going to be put in cpp-tutorial, it should be much more beginner focused. I would recommend splitting this page in two: A beginner introduction in cpp-tutorial and a RNG deep-dive somewhere in the resources section.

wiki/cpp-tutorial/random.md

jeremy-rifkin · 2026-02-27T19:11:45Z

wiki/cpp-tutorial/random.md

+Mersenne Twister engine are large internal state (624 \* `sizeof(std::uint_fast32_t)` bytes) and difficulty of it's
+seeding.


Seeding is no more difficult than any other C++ RandomNumberEngine

The articles I've read online suggested otherwise but after reading through the standard it seems that there is a specific overload that solves this issue.
https://eel.is/c++draft/rand.eng.mers#6

jeremy-rifkin · 2026-02-27T19:13:11Z

wiki/cpp-tutorial/random.md

+for generating a deterministic sequence of numbers that appear random. PRNGs maintain an internal state that is updated
+each time a new number is generated. The initial state of the PRNG is called the seed and the process of setting the
+initial state is called seeding. Two instances of the same PRNG initialized with the same seed will produce identical
+sequences of numbers, which is important for reproducibility of statistical simulations.


Probably much more detail here than is necessary for beginners

Simplified the wording a bit but kept mostly the same.

jeremy-rifkin · 2026-02-27T19:14:19Z

wiki/cpp-tutorial/random.md

+| default_random_engine | implementation defined    |
+| minstd_rand0          | linear congruential       |
+| minstd_rand           | linear congruential       |
+| mt19937               | mersenne twister          |
+| mt19937_64            | mersenne twister          |
+| ranlux24              | subtract with carry       |
+| ranlux48              | subtract with carry       |
+| knuth_b               | minstd_rand0 with shuffle |
+| philox4x32 (C++26)    | counter-based philox      |
+| philox4x64 (C++26)    | counter-based philox      |


I'd recommend focusing just on mt19937 but mentioning as an aside that these other options exist

Kept the table but added some notes

jeremy-rifkin · 2026-02-27T19:14:56Z

wiki/cpp-tutorial/random.md

+initial state is called seeding. Two instances of the same PRNG initialized with the same seed will produce identical
+sequences of numbers, which is important for reproducibility of statistical simulations.
+
+In the [C++ standard library](https://en.cppreference.com/w/cpp/header/random), random engines are callable objects that


We should explain why rand() is bad / insufficient

I added 1 paragraph about it. Quite unsure about the wording

Co-authored-by: Jeremy Rifkin <51220084+jeremy-rifkin@users.noreply.github.com>

jeremy-rifkin

Thanks for the changes! I've left some more comments below. The main structural issue from before still stands: This is too much of a deep-dive into random number generation for a tutorial article. There is a lot of great information here which would be great to have in the resources section of the wiki. I would say LCG, seed_seq, predefined generators table, and philox all belong in a resources page. For the beginner article, just focusing on rand(), a random engine, a random device, std::default_random_engine/std::mt19937, and the three most important distributions should be good. Then linking to the resource page for more in-depth information would be perfect.

jeremy-rifkin · 2026-03-06T22:39:37Z

wiki/cpp-tutorial/sidebar.ts

+            {
+                text: "Random",
+                link: "/cpp-tutorial/random",
+                collapsed: true,


Suggested change

collapsed: true,

jeremy-rifkin · 2026-03-06T22:40:21Z

wiki/cpp-tutorial/random.md

+---
+bot_article: |
+  # Generating Random Numbers in C++
+  ## Example: Printing Ten Random Dice Rolls


Suggested change

## Example: Printing Ten Random Dice Rolls

Simple example of random number generation in C++:

jeremy-rifkin · 2026-03-06T22:57:36Z

wiki/cpp-tutorial/random.md

+  #include <random>
+  #include <iostream>
+
+  int main() {
+    // initialize a random device
+    std::random_device dev;
+
+    // seed default_random_engine
+    std::default_random_engine gen{dev()};
+
+    // initialize a uniform integer distribution
+    std::uniform_int_distribution<int> dis{1, 6};
+
+    // roll the dice
+    for (int i = 0; i < 10; ++i) {
+        std::cout << dis(gen) << ' ';
+    }
+  }


Succinctness is important in a bot article

Suggested change

#include <random>

#include <iostream>

int main() {

// initialize a random device

std::random_device dev;

// seed default_random_engine

std::default_random_engine gen{dev()};

// initialize a uniform integer distribution

std::uniform_int_distribution<int> dis{1, 6};

// roll the dice

for (int i = 0; i < 10; ++i) {

std::cout << dis(gen) << ' ';

}

}

#include <random>

#include <iostream>

int main() {

std::random_device dev; // for seeding

std::default_random_engine rng{dev()};

std::uniform_int_distribution<int> dist{1, 6};

for (int i = 0; i < 10; ++i) {

std::cout << dist(rng) << ' ';

}

}

jeremy-rifkin · 2026-03-06T23:01:33Z

wiki/cpp-tutorial/random.md

+Unlike the C `rand()` function, which relies on common shared seed via `srand()`, the C++ random engines are independent
+and each one has its own seed. This ensures thread safety, whereas C `rand()` does not. Another thing worth mentioning
+about `rand()` is that it is implementation defined and can vary system to system. The C++ random library should be
+always preferred.


This doesn't really capture why rand() is bad. Yes, it is implementation-defined and global, but the most important practical reason is poor randomness quality in all major implementations. rand() % n being biased could also be mentioned.

jeremy-rifkin · 2026-03-06T23:06:16Z

wiki/cpp-tutorial/random.md

+# Generating Random Numbers
+
+A [Pseudorandom Number Generator (PRNG)](https://en.wikipedia.org/wiki/Pseudorandom_number_generator) is an algorithm
+for generating a sequence of (almost) random numbers. PRNGs maintain an internal state that is updated each time a new


How about "numbers that appear random" instead of "almost random"

jeremy-rifkin · 2026-03-06T23:08:07Z

wiki/cpp-tutorial/random.md

+
+## Seed Sequence
+
+Seed sequence (`std::seed_seq`) is an utility in the standard library for converting a small number of inputs into a


Suggested change

Seed sequence (`std::seed_seq`) is an utility in the standard library for converting a small number of inputs into a

Seed sequence (`std::seed_seq`) is a utility in the standard library for converting a small number of inputs into a

jeremy-rifkin · 2026-03-06T23:14:17Z

wiki/cpp-tutorial/random.md

+## Seed Sequence
+
+Seed sequence (`std::seed_seq`) is an utility in the standard library for converting a small number of inputs into a
+higher quality seed (does not contain large areas of zeros/ones) suitable for seeding PRNGs with large internal state


I don't think "does not contain large areas of zeros/ones" is really useful for beginners. It isn't really accurate to say it creates a "higher quality seed" as it can't magically increase entropy, but the mixing it does can improve distribution / bias.

jeremy-rifkin · 2026-03-06T23:23:17Z

wiki/cpp-tutorial/random.md

+    // initialize a uniform real distribution
+    std::uniform_real_distribution<double> dis{0.0, 1.0};
+
+    // generate random numbers in the interval [0, 1)


Might be good to talk about the range

jeremy-rifkin · 2026-03-06T23:24:09Z

wiki/cpp-tutorial/random.md

+        double random_number = dis(gen);
+        std::cout <<  random_number << std::endl;


Suggested change

double random_number = dis(gen);

std::cout << random_number << std::endl;

std::cout << dis(gen) << std::endl;

jeremy-rifkin · 2026-03-06T23:26:27Z

wiki/cpp-tutorial/random.md

+| default_random_engine | implementation defined    | Reproducibility is not important       |
+| minstd_rand0          | linear congruential       | Small internal state                   |
+| minstd_rand           | linear congruential       | Small internal state                   |
+| mt19937               | mersenne twister          | Generally should be preferred          |
+| mt19937_64            | mersenne twister          | Generally should be preferred          |
+| ranlux24              | subtract with carry       | Statistical quality                    |
+| ranlux48              | subtract with carry       | Statistical quality                    |
+| knuth_b               | minstd_rand0 with shuffle | Almost no reason to use it             |
+| philox4x32 (C++26)    | counter-based philox      | Good for multi-threaded applications\* |
+| philox4x64 (C++26)    | counter-based philox      | Good for multi-threaded applications\* |
+
+\*Not yet implemented


The summary column here is largely editorializing. Noting that philox isn't implemented will quickly become outdated (and gcc actually already supports it).

C++ PRNG article

ce29b3e

jeremy-rifkin reviewed Feb 27, 2026

View reviewed changes

ProfessionalMenace and others added 2 commits February 27, 2026 20:57

Typos

1fe1e92

Co-authored-by: Jeremy Rifkin <51220084+jeremy-rifkin@users.noreply.github.com>

beginnerification

0c3a8f1

jeremy-rifkin reviewed Mar 6, 2026

View reviewed changes

		Mersenne Twister engine are large internal state (624 \* `sizeof(std::uint_fast32_t)` bytes) and difficulty of it's
		seeding.

	## Example: Printing Ten Random Dice Rolls
	Simple example of random number generation in C++:


		## Seed Sequence

		Seed sequence (`std::seed_seq`) is an utility in the standard library for converting a small number of inputs into a

	Seed sequence (`std::seed_seq`) is an utility in the standard library for converting a small number of inputs into a
	Seed sequence (`std::seed_seq`) is a utility in the standard library for converting a small number of inputs into a

		double random_number = dis(gen);
		std::cout << random_number << std::endl;

	double random_number = dis(gen);
	std::cout << random_number << std::endl;
	std::cout << dis(gen) << std::endl;

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ProfessionalMenace commented Feb 21, 2026

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