Construction a vector from the concatenation of 2 vectors

Question

Is there a way to construct a vector as the concatenation of 2 vectors (Other than creating a helper function?)

For example:

Answer 1

I think you have to write a help function. I'd write it as:

std::vector concatenate(const std::vector& lhs, const std::vector& rhs)
{
    auto result = lhs;
    std::copy( rhs.begin(), rhs.end(), std::back_inserter(result) );
    return result;
}

The call it as:

    const auto concatenation = concatenate(first, second);

If the vectors are likely to be very large (or contain elements that are expensive to copy), then you might need to do a reserve first to save reallocations:

std::vector concatenate(const std::vector& lhs, const std::vector& rhs)
{
    std::vector result;
    result.reserve( lhs.size() + rhs.size() );
    std::copy( lhs.begin(), lhs.end(), std::back_inserter(result) );
    std::copy( rhs.begin(), rhs.end(), std::back_inserter(result) );
    return result;
}

(Personally, I would only bother if there was evidence it was a bottleneck).