Remove trailing comma in CSV file written for a vector using copy and ostream_iterator

Question

I have the following function, which writes a vector to a CSV file:

#include 
#include 
#include 
#include         


        

Answer 1

As you observed, copying via std::copy doesn't do the trick, one additional , is output. There is a proposal that will probably make it in the future C++17 standard: ostream_joiner, which will do exactly what you expect.

However, a quick solution available now is to do it manually.

for(auto it = std::begin(*pdata); it != std::end(*pdata); ++it)
{
    if (it != std::begin(*pdata))
        std::cout << ",";
    std::cout << *it;
}

Answer 2

I'd omit printing the comma by treating the first element special:

if (!pdata->empty()) {
    os << pdata->front();
    std::for_each(std::next(pdata->begin()), pdata->end(),
                  [&os](auto&& v){ os << ", " << v; });
}

Obviously, this code goes into a function printing a printable range adapter.

Answer 3

There are many ways, besides already listed:

std::string sep;
for (const auto& x : *pdata) {
    os << x << clusAvg;
    sep = ", ";
}

or

auto it = pdata->begin();
if (it != pdata->end()) {
    os << *it;
    for(; it != pdata->end(); ++it)
        os << ", " << *it;
}

or

auto it = pdata->end();
if (it != pdata->begin()) {
    --it;
    std::copy(pdata->begin(), it, ostream_iterator<double>(os, ", "));
    os << *it;
}