可以将增压累加器用作类成员

Question

我正在尝试使用增压累加器来计算滚动平均值.当我像这样声明变量内联时:

#include <iostream>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/rolling_mean.hpp>

using namespace boost::accumulators;

int main()
{
  // Define rolling_mean accumulator
  accumulator_set<double, stats<tag::rolling_mean > > acc(tag::rolling_window::window_size = 5);
    // push in some data ...
    acc(1.2);
    acc(2.3);
    acc(3.4);
    acc(4.5);

    // Display the results ...
    std::cout << "Mean:   " << rolling_mean(acc) << std::endl;

    return 0;
}

它工作得很好.当我将累加器声明为类的成员时,如下所示:

#include <iostream>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/rolling_mean.hpp>

using namespace boost::accumulators;

class DoMean {
private:
  accumulator_set<double, stats<tag::rolling_mean > > m_acc(tag::rolling_window::window_size = 5);

public:

  void addData(double val) {
    this->m_acc(val);
  }

  double getMean(void) {
    return rolling_mean(this->m_acc);
  }
};

int main()
{
  // Define an accumulator set for calculating the mean and the
  // 2nd moment ...
  DoMean meaner;
  meaner.addData(1.2);
  meaner.addData(2.3);
  meaner.addData(3.4);
  meaner.addData(4.5);

  // push in some data ...

  // Display the results ...
  std::cout << "Mean:   " << meaner.getMean() << std::endl;

  return 0;
}

它失败了,给出了编译错误:

accumulators::tag::rolling_window::window_size is not a type
...blah blah, many type template errors etc.

Answer 1

这个问题的正确解决方案是:

#include <iostream>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/rolling_mean.hpp>

using namespace boost::accumulators;

class DoMean {
private:
  accumulator_set<double, stats<tag::rolling_mean > > m_acc;

public:

  DoMean(void): m_acc(tag::rolling_window::window_size = 5) {}

  void addData(double val) {
    this->m_acc(val);
  }

  double getMean(void) {
    return rolling_mean(this->m_acc);
  }
};

int main()
{
  // Define an accumulator set for calculating the mean and the
  // 2nd moment ...
  DoMean meaner;
  meaner.addData(1.2);
  meaner.addData(2.3);
  meaner.addData(3.4);
  meaner.addData(4.5);

  // push in some data ...

  // Display the results ...
  std::cout << "Mean:   " << meaner.getMean() << std::endl;

  return 0;
}

请注意,m_acc的初始化已从其内联的声明移动到初始化列表中.这解决了所有编译器错误.事实上,如果我们考虑一下这里发生了什么,最初尝试在类中使用累加器失败的原因是因为ISO c ++禁止内联成员的初始化.

我们可以用另一个简单的类来演示:

#include <iostream>

class TestInit {
public:
  int m_init = 10;

};

int main() {
  TestInit inits;
  std::cout << "The value: " << inits.m_init << std::endl;

}

现在编译器给我们一个有用的消息:

/home/me/prog/cpp/acctest/testinit.cxx:5:16: error: ISO C++ forbids initialization of member m_init [-fpermissive]
/home/me/prog/cpp/acctest/testinit.cxx:5:16: error: making m_init static [-fpermissive]
/home/me/prog/cpp/acctest/testinit.cxx:5:16: error: ISO C++ forbids in-class initialization of non-const static member m_init