How to write a generic function to print begin and end iterator elements

February 3, 2022

The function below, printloop, is able to print the elements in a collection as below. But if I try to remove the loop and use std::copy, how do I get that version, print, to work?

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>

// this print function doesn't compile
template <typename iter>
void print(iter begin, iter end) {
  std::copy(begin, end, 
     std::ostream_iterator< what type? >(std::cout, "\t"));
}

template <typename iter>
void printloop(iter begin, iter end) {
    while (begin != end) {
        std::cout << *begin << '\t';
        begin++;
    }
}

int main() {
    std::vector<int> vec {1,2,3,4,5};
    printloop(vec.begin(), vec.end());  // works ok
    print(vec.begin(), vec.end()); // how to get working?
}

>Solution :

You might use iterator_traits:

template <typename iter>
void print(iter begin, iter end) {
  using value_type = typename std::iterator_traits<iter>::value_type;
  std::copy(begin, end, std::ostream_iterator<value_type >(std::cout, "\t"));
}

Demo