all of the answers for using ostream_iterator and copy to turn a string to hex in c++ on Stack Overflow are wrong. This works.

hex.cc

#include <iostream>
#include <vector>
#include <algorithm>
#include <sstream>
#include <iomanip>
using namespace std;
 
template <typename T>
struct hexwrite
{
    hexwrite(T v_) : v(v_) {}
    T v;
};

template <typename T>
std::ostream& operator<< (std::ostream& ostr, const hexwrite<T> &fwv)
{
    return ostr << std::setw(2)<< std::setfill('0')<< std::hex << fwv.v;
}

   int main()
   {
    vector<char> data = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18};
    ostringstream hexout;
    copy(data.begin(), data.end(), ostream_iterator< hexwrite<int> >(hexout, " "));
    cout << hexout.str() << endl;
    hexout.clear();
    for(auto d : data)
      hexout << d;
    cout << hexout.str() << endl;
    hexout.clear();
    for(auto const &d : data)
      hexout << setw(2) << hex << setfill('0') << d;
    cout << hexout.str() << endl;
    hexout.clear();
    
    return 0;
    }