Concatenating two std::vectors

Question

How do I concatenate two std::vectors?

Answer 1

If your goal is simply to iterate over the range of values for read-only purposes, an alternative is to wrap both vectors around a proxy (O(1)) instead of copying them (O(n)), so they are promptly seen as a single, contiguous one.

std::vector A{ 1, 2, 3, 4, 5};
std::vector B{ 10, 20, 30 };

VecProxy AB(A, B);  // ----> O(1)!

for (size_t i = 0; i < AB.size(); i++)
    std::cout << AB[i] << " ";  // ----> 1 2 3 4 5 10 20 30

Refer to https://stackoverflow.com/a/55838758/2379625 for more details, including the 'VecProxy' implementation as well as pros & cons.