I declare I use it:

#include <boost/circular_buffer.hpp>

I make my function:

double calculateStdDev(const boost::circular_buffer<double>& input, double& mean, double& variance, double& stddev) {

  if (input.empty()) return 0.0;

  boost::circular_buffer<double>::const_iterator it = input.begin(), end = input.end();

  double M = *it;

  double Q = 0.0;

  unsigned int count = 1;

  ++it;

  while (it != end) {

    unsigned int k = count;

    ++count;

    double del = *it - M;

    unsigned int j = k + 1;

    Q += k * (del * del) / j;

    M += del / j;

    ++it;

  }

  variance = Q / (count - 1);

  stddev = std::sqrt(variance);

  mean = M;

  return stddev;

}

This function doesn't need to know are care about the number of items in the buffer.  It just makes one pass through the data, from it = inut.begin() to input.end().  This particular algorithm, BTW, provides a solution that is MUCH faster and much more accurate in some cases, than the two pass algorithm, and is much more accurate than the other single pass algorithms you may see recommended.  But that isn't the point.

In the header that provides the prototypes for the functions in this particular CPP file, I have:

double calculateStdDev(const boost::circular_buffer<double>& input, double& mean, double& variance, double& stddev);

And gcc v 4.3.4 gives me the following error:

../../include/distribution.moments.hpp:9: error: wrong number of template arguments (1, should be 2)

/usr/local/include/boost/circular_buffer/base.hpp:70: error: provided for 'template<class T, class Alloc> class boost::circular_buffer'

I am not sure I understand why.

Does this mean that I have to make calculateStdDev a template function?  E.g.:

template <typename T>

double calculateStdDev(const boost::circular_buffer<double, T>& input, double& mean, double& variance, double& stddev) {

                // and put the entire implementation here in the header instead of in the cpp file with the overloads for other types such as std::vector)

}

But, if that is the case, why is it possible to instantiate such a buffer using the following (as in the example)?

boost::circular_buffer<int> cb(3);

I must have missed something, but I don't know what.

Cheers

Ted