Appending a vector to a vector [duplicate]

Question

Assuming I have 2 standard vectors:

vector<int> a; vector<int> b; 

Let's also say the both have around 30 elements.

• How do I add the vector b to the end of vector a?

The dirty way would be iterating through b and adding each element via vector<int>::push_back(), though I wouldn't like to do that!

Answer 1

a.insert(a.end(), b.begin(), b.end()); 

or

a.insert(std::end(a), std::begin(b), std::end(b)); 

The second variant is a more generically applicable solution, as b could also be an array. However, it requires C++11. If you want to work with user-defined types, use ADL:

using std::begin, std::end; a.insert(end(a), begin(b), end(b)); 

Answer 2

std::copy (b.begin(), b.end(), std::back_inserter(a)); 

This can be used in case the items in vector a have no assignment operator (e.g. const member).

In all other cases this solution is ineffiecent compared to the above insert solution.