boost accumulator_set: expect主表达式

Question

我是一个促进图书馆发展的新人。我想要一个程序，可以计算距离向量的最小、最大、平均和方差(类型为std::vector < double >)，我编写了以下代码

std::vector < double > dist_err;
// ... do something with dist_err
boost::accumulators::accumulator_set
< 
    double, 
    boost::accumulators::stats
    <
        boost::accumulators::tag::min , 
        boost::accumulators::tag::max ,
        boost::accumulators::tag::mean,
        boost::accumulators::tag::variance
    > 
> stat_acc;
std::for_each(dist_err.begin(), dist_err.end(), boost::bind < void > (boost::ref(stat_acc), boost::mpl::placeholders::_1));
std::cout << "min[distance error]: " << boost::accumulators::min      (stat_acc) << std::endl;
std::cout << "MAX[distance error]: " << boost::accumulators::max      (stat_acc) << std::endl;
std::cout << "  E[distance error]: " << boost::accumulators::mean     (stat_acc) << std::endl;
std::cout << "VAR[distance error]: " << boost::accumulators::variance (stat_acc) << std::endl;

但是程序在std::for_each(dist_err.begin(), dist_err.end(), boost::bind < void > (boost::ref(stat_acc), boost::mpl::placeholders::_1));行给了我一个错误，它说

error: expected primary-expression before ')' token
std::for_each(dist_err.begin(), dist_err.end(), boost::bind < void > (boost::ref(stat_acc), boost::mpl::placeholders::_1));

有人能给我一些关于如何解决这个错误的提示吗？

Answer 1

问题是，您在代码中使用的是boost::mpl::placeholders::_1，它不使用MPL。相反，只需说_1。