提高accumulator_set：期望主表达式

Question

I am a new to Boost library. I want a program that could compute the min, max, mean and variance of a distance vector (of type std::vector < double > ) and I wrote the following code

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;

But the program gives me an error at line std::for_each(dist_err.begin(), dist_err.end(), boost::bind < void > (boost::ref(stat_acc), boost::mpl::placeholders::_1)); and it says

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));

Could someone please give me some hint on how to solve this error?

Answer 1

The problem is you are using boost::mpl::placeholders::_1 inside code which doesn't use MPL. Instead, just say _1 .