Is there a limit on the number of values added to a boost::accumulator?

Is there a limit on how many values that can be added to a boost::accumulator? If a large number of entries were added, is there any point in which the accumulator would cease to work properly or is the internal algorithm robust enough to account for a set of values approaching infinity?

#include <iostream>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/mean.hpp>
#include <boost/accumulators/statistics/moment.hpp>
using namespace boost::accumulators;

int main()
{
    // Define an accumulator set for calculating the mean and the
    // 2nd moment ...
    accumulator_set<double, stats<tag::mean, tag::moment<2> > > acc;

    // push in some data ...
    for (std::size_t i=0; i<VERY_LARGE_NUMBER; i++)
    {
      acc(i);
    }


    // Display the results ...
    std::cout << "Mean:   " << mean(acc) << std::endl;
    std::cout << "Moment: " << moment<2>(acc) << std::endl;

    return 0;
}

Solution

If your int is a 32 bit integer, you'll get a signed integer overflow at 46341 * 46341 when calculating moment<2> and your program therefore has undefined behavior.

To avoid that, cast i to the type you're using in the accumulator:

acc(static_cast<double>(i));

This will now have the same limits as a normal double. You can add as many elements as you'd like to it as long as you don't exceed the limit (std::numeric_limits<double>::max()) for a double in the internal moment calculations (x² for moment<2> or a sum that exceeds the limit).