Thread: don't understand myVector.reserve(numSpaces)

I'm going through a book and I've looked this up, but don't understand why (or maybe I have to) use reserve. Since it is a vector why is there a need to reserve memory? Is it just a way so that it doesn't double the memory off the heap or something (me guessing)?

here is the code I am looking at:

Code:

class Farm
{
public:
    Farm(int spaces = 1);
    //.... more stuff goes here

private:
    vector<myFarmAnimalClassObject> m_farmAnimal;
};

//=============Constructor: reserve used below=========
Farm::Farm(int spaces)
{
    m_farmAnimal.reserve(spaces)    //  <===  reserve?
}

Thanks again! I never thought about iterators. Reading that artical made me think about other things I don't know and will have to experiement with (pointers to an unsorted list which is then sorted - I'm sure it comes out ok, but I've never thought of it till now). I've mostly just messed around with python which doesn't really use pointers.

Well, now its more fun with farm animals! ! !