[Boost-users] [Random] Documentation enhancement

From: Richard Jennings (Richard.Jennings_at_[hidden])
Date: 2005-03-04 06:30:24

I would like to suggest an enhancement to the documentation for the
random library.
 
The documentation for the number generators advises not to construct
generators frequently for various reasons.  On some platforms there
could also be an issue with memory use where the generators are created
on the stack.
 
I have used the suggested mt19937 generator that is about 5000 bytes in
size on my system.  If I create two of these on the stack then I get a
crash.  I followed the "very quick start" example that creates the
generator on the stack and has a variate_generator like this:
 
  boost::mt19937 rng;
  boost::uniform_int<> six(1,6)
  boost::variate_generator<boost::mt19937, boost::uniform_int<> >
           die(rng, six);

Thus, each instance of variate_generator has a copy of the generator
too.  The random_demo.cpp works just fine because it uses an alias for
the generator:

 boost::variate_generator<base_generator_type&, boost::uniform_real<> >

thus multiple copies of the variate_generator on the stack are fine.

I guess what this comes down to is a warning about creating multiple
instances on the stack of generators and/or variate_generators where the
engine template parameter to variate_generator is a engine rather than a
pointer or reference to an engine.

Richard