Random numbers in Qt

Mimoid

Hi! I want random number for a few thousands numbers range, but i dont know how to do it.
This is my code and this gives me each program run the same combination of numbers. For example 2,7,5,9... And next time when i run program is the same sequence...

int number=tab.size(); //for now size of my array is 1511
    random = qrand() % number;

This is code of the same program but in console and it works good.

srand(time(NULL));
    random=rand()%tab.size();

It doesnt need to be super perfect random, but although has a different order in each run.

? Offline

Hi! You forgot to initialize the prng. See: void qsrand(uint seed).

SGaist

Hi,

Just add qsrand and you should be good to go.

Paul Colby

Hi @Mimoid,

Your console program works as you want because you're seeding the rand function via the srand call. The Qt equivalent (thread-safe wrapper) is qsrand. So try something like:

qsrand(time(NULL));
...
random = qrand() % number;

Cheers.

SGaist

Well... 3 times the same answer :D

? Offline

@SGaist Must be correct then :)

VRonin

I'll give a different answer then, use C++11 random. already thread safe and you can generate random numbers according to different probability distribution:
http://www.cplusplus.com/reference/random/

SGaist

@VRonin you rebel ! ;) :D