Concatenating two std::vectors

Question

How do I concatenate two std::vectors?

Answer 1

If you are interested in strong exception guarantee (when copy constructor can throw an exception):

template
inline void append_copy(std::vector& v1, const std::vector& v2)
{
    const auto orig_v1_size = v1.size();
    v1.reserve(orig_v1_size + v2.size());
    try
    {
        v1.insert(v1.end(), v2.begin(), v2.end());
    }
    catch(...)
    {
        v1.erase(v1.begin() + orig_v1_size, v1.end());
        throw;
    }
}

Similar append_move with strong guarantee can't be implemented in general if vector element's move constructor can throw (which is unlikely but still).