C++ :: Filling A Vector With Elements?

I'm writing a program with a class containing a private std::vector<bool>. I chose bool because the vector represents a 2D array (think grid) and I only need 2 states per cell. I kept it one-dimensional as this hardly complicates things.

My problem is that I don't know how to initialize the vector, i.e. fill it with 0's.

The grid's resolution is not known at compile time, so I imagine I have to set the size (and content) of the vector in the class constructor.

Here's what I have tried among several things:

Code: World::World(const u_short worldsize)
{
grid.reserve(worldsize * worldsize); // grid is the private vector; square dimensions.
std::fill(grid.begin(), grid.end(), 0);
std::cout << grid.size();
} The output is 0. Only std::vector::push_back seems to have an effect on size(), but judging by its description, it doesn't look like the right candidate to populate a vector with zeros. Correct me if I'm wrong.

Frankly I expected line 3 to set the vector's size.