C++: High Precision Random Double Numbers

Question

This is a follow up question on an answer on this page:

How to generate random double numbers with high precision in C++?

#include <iostream>
#include <random>
#include <iomanip>    

int main()
{
    std::random_device rd;

    std::mt19937 e2(rd());

   std::uniform_real_distribution<> dist(1, 10);

   for( int i = 0 ; i < 10; ++i )
   {
      std::cout << std::fixed << std::setprecision(10) << dist(e2) << std::endl ;
   }

  return 0 ;
}

The answer works fine but I had a hard time to realize how to put the output of this code in a double variable instead of printing it to stdout. Can anyone help with this?

Thanks.

if I just run "double var = dist(e2);" it just gives 6 digits... — Konstantinos Kamaropoulos, Jan 29 '16 at 15:31
Then you should show that in the question. right now it is unclear what you are asking. — NathanOliver, Jan 29 '16 at 15:33
hmm... Does the variable still contain the rest digits and std::setprecision(10) just sets how many will std::cout print? — Konstantinos Kamaropoulos, Jan 29 '16 at 15:34

score 3 · Accepted Answer · answered Jan 29 '16 at 15:35

3

You're getting confused between actual precision and displayed precision - try this:

#include <iostream>
#include <random>
#include <iomanip>    

int main()
{
    std::random_device rd;
    std::mt19937 e2(rd());
    std::uniform_real_distribution<> dist(1, 10);

    double v = dist(e2);   // get a random double at full precision

    std::cout << std::fixed << std::setprecision(10) << v << std::endl;
                           // display random double with 10 digits of precision
    return 0;
}

answered Jan 29 '16 at 15:35

Paul R

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Yeah, I got a little confused with that, thinking that what the variable contained depended on the setprecision function. Thanks – Konstantinos Kamaropoulos Jan 29 '16 at 15:38
2

No problem - it's a common source of confusion. – Paul R Jan 29 '16 at 15:39
@PaulR I also have similar question [here](http://stackoverflow.com/questions/35258164/how-to-prevent-numbers-from-showing-up-in-scientific-notations). If possible can you help me out. – user1950349 Feb 14 '16 at 17:06

C++: High Precision Random Double Numbers

1 Answers1