c++ - boost accumulator_set : expect primary expression

Question

我是 Boost 库的新手。我想要一个可以计算距离 vector (类型 std::vector < double > )的最小值、最大值、均值和方差的程序，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));

有人可以给我一些关于如何解决这个错误的提示吗？

Answer 1

问题是您在不使用 MPL 的代码中使用 boost::mpl::placeholders::_1。相反，只需说 _1。