Question

in an answer to this question I have been informed that my problems lie to the call to a copy constructor in the code below. However, I just don’t see where it’s being invoked. Nowhere am I doing something like agents[1] = agents[0]; although clearly I don’t understand something. Where is this copying occurring and how can I change it so it’s just making new objects each time?

I have been

int main()
{
    Level* level;
    std::vector<Agent> agents;

    level = new Level(agents);

    for (int i = 0; i < 1; i++) // this will be more than 1 in the future.
    {
        agents.push_back(Agent(100, *level, agents, level->Pickups(), D3DXCOLOR(1.0F, 0.4f, 0.4f, 1.0f)));
    }

    delete level;

}

Answer 1

As others have said, push_back will insert a copy into the vector.

If you have a compiler with some C++11 support it’s possibly that you can avoid this copy by constructing the object directly into the vector. The new emplace_back function does this:

agents.emplace_back(100, *level, agents, level->Pickups(), D3DXCOLOR(1.0F, 0.4f, 0.4f, 1.0f));

In addition, if the compiler has C++11 support for move semantics, push_back will do a move operation instead of a copy operation if a move constructor is available for Agent, because you’re passing it a temporary.