C++ Concatenating Vectors


Example

One std::vector can be append to another by using the member function insert():

std::vector<int> a = {0, 1, 2, 3, 4};
std::vector<int> b = {5, 6, 7, 8, 9};

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

However, this solution fails if you try to append a vector to itself, because the standard specifies that iterators given to insert() must not be from the same range as the receiver object's elements.

c++11

Instead of using the vector's member functions, the functions std::begin() and std::end() can be used:

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

This is a more general solution, for example, because b can also be an array. However, also this solution doesn't allow you to append a vector to itself.

If the order of the elements in the receiving vector doesn't matter, considering the number of elements in each vector can avoid unnecessary copy operations:

if (b.size() < a.size())
  a.insert(a.end(), b.begin(), b.end());
else
  b.insert(b.end(), a.begin(), a.end());