Why is my first pseudo-random integer always zero?

Question

I have several runs through the loop and am trying to create a different, but pseudo-random integer in each run. Unfortunately, the first number created is always 0.

Interestingly, this only takes place for generating random integers via std::uniform_int_distribution<int> . If I replace it with std::uniform_real_distribution<double> , I will get the desired behavior.

Are there any special rules for creating a seed, or why is the first generated integer always 0?

Below is a minimal example of my problem:

 #include <iostream> #include <random> int main() { int number_of_runs = 5; for (int i = 0; i != number_of_runs; ++i) { // create random engine std::default_random_engine my_generator; unsigned my_seed = i; // should be pseudo-random, but different for every run my_generator.seed(my_seed); // create distribution int upper_limit = (i+1)*10; // only example, but different for every run std::uniform_int_distribution<int> my_distribution(0, upper_limit); // create random numbers std::cout << "run #" << i+1 << "\n"; std::cout << "random 1: " << my_distribution(my_generator) << "\n"; std::cout << "random 2: " << my_distribution(my_generator) << "\n"; std::cout << "random 3: " << my_distribution(my_generator) << "\n"; std::cout << "random 4: " << my_distribution(my_generator) << "\n"; std::cout << "random 5: " << my_distribution(my_generator) << "\n" << std::endl; } return 0; } 

The result is, for example:

 run #1: random 1: 0 random 2: 1 random 3: 8 random 4: 5 random 5: 5 run #2 random 1: 0 random 2: 2 random 3: 15 random 4: 9 random 5: 11 run #3 random 1: 0 random 2: 8 random 3: 15 random 4: 28 random 5: 2 run #4 random 1: 0 random 2: 16 random 3: 10 random 4: 15 random 5: 24 run #5 random 1: 0 random 2: 26 random 3: 1 random 4: 42 random 5: 6