member reference base type 'double [10]' is not a structure or union

Question

I created a fixed array e_pt[10] initialised with zeros. I then filled in some values into the array e_pt. I would then like to find the index of the largest element in the array. The code is shown below.

double e_pt[10] = {};

for (size_t lep_i=0; lep_i<lep_n; lep_i++) // loop over leptons
{
    if (lep_type->at(lep_i) == 11)   // record kinematic info of electrons into array
    {
        e_pt[lep_i] = lep_pt->at(lep_i); 
    }

} // end of loop over leptons       

int e_index = std::distance(e_pt.begin(), std::max_element(e_pt.begin(), e_pt.end()));

However when I try to compile this, the following error occurs:

member reference base type 'double [10]' is not a structure or union

It is refering to the action e_pt.begin() being invalid.

What is wrong here?

Answer 1

std::max_element(e_pt.begin(), e_pt.end()) Native array doesn't have methods like that.

It should be

std::max_element(std::begin(e_pt), std::end(e_pt));

This error relates to use of . operator on array. Your loop can be simpler, if lep_n is size of lep_pt and lep_pt is container compatible with C++ ranges.

size_t lep_i = 0;
for (auto pt : lep_pt)
  if (lep_type->at(lep_i) == 11)   
    e_pt [lep_i++] = pt;

Or vice versa relative to lep_type.