Thread: Constructor question

If I create a vector vec by writing

Code:

vector<int> vec;

is the constructor of the vector class called or not?
If not, is vec.size() is undefined?

I know I can always write

Code:

vector<int> vec();

or

Code:

vector<int> vec() = new vector<int>;

etc, but I think I have a lot of old programs where I haven't, and I would like to know if I have to modify them.