In C++20 the full program, retaining the same algorithm, can look like this: #include <algorithm> #include <iterator> #include <vector> #includ

In C++20 the full program, retaining the same algorithm, can look like this: #include <algorithm> #include <iterator> #include <vector> #include <iostream> using namespace std::ranges; int main() { std::vector a = {1,2,3,4}; std::vector b = {5,6,3,4}; sort(a); sort(b); decltype(a) c; set_union (a, b, back_inserter(c)); copy(c, std::ostream_iterator<int>(std::cout, "\n")); } https://gcc.godbolt.org/z/44Ksf1hK8 https://gcc.godbolt.org/z/44Ksf1hK8 Note the value type deduction when declaring the vectors, the use of back_inserter to avoid having to resize the result (c) vector, the use of std::ranges to do away with all the begin + end crapola, and the way ranges and iterators are inter-mixed. C++ is always going to be a bit more verbose in trivial cases, but it's not that bad, and exposes a lot more flexibility in complex ones.