g++ & rand() in Cygwin

g++ & rand() in Cygwin

[Alex Vinokur]

------ foo.cpp ------
#include <cstdlib>
#include <iostream>
using namespace std;
int main ()
{
  cout << rand() << endl;
  cout << rand() << endl;
  return 0;
}
---------------------


// g++ version 3.3.3 (cygwin special)

$ g++ foo.cpp

The program below generates the following output:
-----------
0
1481765933
-----------

First pseuso-random number is 0.

Is it by purpose?

-- 
 Alex Vinokur
     email: alex DOT vinokur AT gmail DOT com
     http://mathforum.org/library/view/10978.html
     http://sourceforge.net/users/alexvn

Re: g++ & rand() in Cygwin

[Brian Budge]

Hi Alex -

You should seed the rng first before using it.  Also, there are much
better rngs out there than rand (though it's much better than it used
to be).  I tend to plug for  Mersenne Twister which is both faster,
produces better random numbers, and can be used in a parallel
programming environment.

  Brian


On Sat, 12 Mar 2005 08:04:59 +0200, Alex Vinokur
<alexvn@users.sourceforge.net> wrote:
> ------ foo.cpp ------
> #include <cstdlib>
> #include <iostream>
> using namespace std;
> int main ()
> {
>   cout << rand() << endl;
>   cout << rand() << endl;
>   return 0;
> }
> ---------------------
> 
> // g++ version 3.3.3 (cygwin special)
> 
> $ g++ foo.cpp
> 
> The program below generates the following output:
> -----------
> 0
> 1481765933
> -----------
> 
> First pseuso-random number is 0.
> 
> Is it by purpose?
> 
> --
>  Alex Vinokur
>      email: alex DOT vinokur AT gmail DOT com
>      http://mathforum.org/library/view/10978.html
>      http://sourceforge.net/users/alexvn
> 
>

Re: g++ & rand() in Cygwin

[Gerrit P. Haase]

Alex Vinokur wrote:
> ------ foo.cpp ------
> #include <cstdlib>
> #include <iostream>
> using namespace std;
> int main ()
> {
>   cout << rand() << endl;
>   cout << rand() << endl;
>   return 0;
> }
> ---------------------
> 
> 
> // g++ version 3.3.3 (cygwin special)
> 
> $ g++ foo.cpp
> 
> The program below generates the following output:
> -----------
> 0
> 1481765933
> -----------
> 
> First pseuso-random number is 0.
> 
> Is it by purpose?

I don't know.  I use MT for random number generation:

http://anfaenger.de/cygwin/MersenneTwister/


Gerrit
-- 
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Action Soccer: http://www.action-soccer.de/?lv=de&id=505
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Re: g++ & rand() in Cygwin

[Nathan Sidwell]

Gerrit P. Haase wrote:
> Alex Vinokur wrote:


>> First pseuso-random number is 0.

Random nnumber generators generally need to be seeded with a random
seed.  This naively strange behaviour allows you to get consistent
sequences of random numbers, which is generally necessary for regression
testing and debugging.

nathan

-- 
Nathan Sidwell    ::   http://www.codesourcery.com   ::     CodeSourcery LLC
nathan@codesourcery.com    ::     http://www.planetfall.pwp.blueyonder.co.uk