srand

I have C++ code that relies heavily on sampling (using rand()), but I want it to be reproducible. So in the beginning, I initialize srand() with a random seed and print that seed out. I want others to be able to run the same code again but initializing srand() with that same seed and get exactly the same answer as I did. But under what circumstances is that guaranteed? I suppose that works only if the binaries are compiled with the same compiler on the same system? What are other factors that might make the answer differ from the one I got initially? The solution is to use the same code in all

In a function, I want to generate a list of numbers in range: (This function will be called only once when executing the program.) void DataSet::finalize(double trainPercent, bool genValidData) { srand(time(0)); printf("%d\n", rand()); // indices = {0, 1, 2, 3, 4, ..., m_train.size()-1} vector<size_t> indices(m_train.size()); for (size_t i = 0; i < indices.size(); i++) indices[i] = i; random_shuffle(indices.begin(), indices.end()); // Output for (size_t i = 0; i < 10; i++) printf("%ld ", indices[i]); puts(""); } The results are like: 850577673 246 239 7 102 41 201 288 23 1 237 After a few

I just found out the hard way that srand(1) resets the PRNG of C(++) to the state before any call to srand (as defined in the reference ). However, the seed 0 seems to do the same, or the state before any call to srand seems to use the seed 0. What’s the difference between those two calls or what is the reason they do the same thing? For example this code ( execute on Ideone ) #include <stdio.h> #include <stdlib.h> int main() { for (int seed = 0; seed < 4; seed++ ) { printf( "Seed %d:", seed); srand( seed ); for(int i = 0; i < 5; i++ ) printf( " %10d", rand() ); printf( "\n"); } return 0; }

I want to write a multiplayer game on iOS platform. The game relied on random numbers that generated dynamically in order to decide what happen next. But it is a multiplayer game so this "random number" should be the same for all device for every player in order to have a consistent game play. Therefor I need a good reliable pseudorandom number generator that if I seed it a same number first than it will keep generate same sequences of random number on all device (iPad/iPhone/iPodTouch) and all OS version. Looks like srand and rand will do the job for me but I am not sure does rand guarantee

I'm using the random_shuffle on a vector like this: #include <algorithm> vector <Card> deck; //some code to add cards to the deck here random_shuffle ( deck.begin(), deck.end() ); When run, the content of the deck is mixed up, but this mixed-up order is kept when I restart the program. Did I miss something? How can I make it truly random? You need to seed the psuedo-random number generator first using srand . #include <algorithm> #include <cstdlib> ... std::srand(std::time(0)); vector <Card> deck; //some code to add cards to the deck here random_shuffle ( deck.begin(), deck.end() ); Note from