ranges/to3.cpp

The following code example is taken from the book
C++23 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2026
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <print>
#include <vector>
#include <functional>
#include <ranges>
#include <chrono>

int main()
{
  std::vector<int> coll{47, 11, 0, 8, 15, -11, 7};
  std::println("coll: {}", coll);

  auto isOdd = [] (auto val) { return val % 2 != 0; };
  auto vecView = coll | std::views::filter(isOdd);
  for (int& elem : vecView) {
    elem = elem * elem;
  }
  std::println("   => {}", coll);

  coll = {47, 11, 0, 8, 15, -11, 7};
  std::println("\ncoll: {}", coll);

  auto vec1 = coll | std::views::filter(isOdd) | std::ranges::to<std::vector>();
  for (int& elem : vec1) {
    elem = elem * elem;
  }
  std::println("   => {}", coll);
  std::println("vec1: {}", vec1);

  coll = {47, 11, 0, 8, 15, -11, 7};
  std::println("\ncoll: {}", coll);

  auto vec2 = coll | std::views::filter(isOdd)
                   | std::ranges::to<std::vector<std::reference_wrapper<int>>>();
  for (int& elem : vec2) {
    elem = elem * elem;
  }
  std::println("   => {}", coll);
}