Re: [Boost-users] Random: How to get a different seed?

Subject: Re: [Boost-users] Random: How to get a different seed?
From: Zoltán Lengyel (katzlengyel_at_[hidden])
Date: 2011-01-24 10:34:03

#include "uniform_int.hpp"
#include "boost/random/variate_generator.hpp"
#include "boost/random/mersenne_twister.hpp"
#include <time.h>

#include <iostream>
using namespace std;
using namespace boost;

time_t T = time(0);
mt19937 gen(T);

int roll_die()
{
    uniform_int<> dist(1, 6);
    variate_generator<mt19937&, uniform_int<> > die(gen, dist);
    return die();
}

int main()
{
    for (int i = 0; i < 5; i++)
        cout << roll_die() << endl;

    return 0;
}

Thanks for your help, it works this way.

On 24 January 2011 15:33, Hernán Leoni <leoni.hernan_at_[hidden]> wrote:

> I think you have to use the time as argument for the generator
>  mt19937 gen(time(0));
>
> 2011/1/24 Zoltán Lengyel <katzlengyel_at_[hidden]>
>
>> Hello,
>> I am trying to make a simple program that can generate random integers in
>> range, using boost::uniform_int.
>>
>>
>> http://www.boost.org/doc/libs/1_45_0/doc/html/boost_random/tutorial.html#boost_random.tutorial.generating_integers_in_a_range
>> This tutorial tells:
>> "We use mt19937<http://www.boost.org/doc/libs/1_45_0/doc/html/boost/mt19937.html>with the default seed as a source of randomness. The numbers produced will
>> be the same every time the program is run. One common method to change this
>> is to seed with the current time (std::time(0) defined in ctime)."
>>
>> I have trouble getting this common method compile and work. Here's a tiny
>> program that works, with the same seed at every run (like what the tutorial
>> does), I have commented out my desperate tries to make the seed change.
>>
>>
>> #include "uniform_int.hpp"
>> #include "boost/random/variate_generator.hpp"
>> #include "boost/random/mersenne_twister.hpp"
>> #include <time.h>
>>
>> #include <iostream>
>> using namespace std;
>> using namespace boost;
>>
>> mt19937 gen;
>> // time_t gen = time(0);
>>
>>
>> int roll_die()
>> {
>>     uniform_int<> dist(1, 6);
>>     variate_generator<mt19937&, uniform_int<> > die(gen, dist);
>>     //boost::variate_generator<time_t, boost::uniform_int<> > die(gen,
>> dist);
>>     return die();
>> }
>>
>>
>> int main()
>> {
>>     for (int i = 0; i < 5; i++)
>>         cout << roll_die() << endl;
>>
>>     return 0;
>> }
>>
>> So, I would be glad, if someone could fix this for me, to have a different
>> seed (depending on system time) at each start.
>> Thanks!
>> _______________________________________________
>> Boost-users mailing list
>> Boost-users_at_[hidden]
>> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>
>
>
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