C++ functions not working on OSX

Hello

I'm new to programming, so I hope my problem will be easy to resolve. My problem:

Up to now, I've programmed at school on workstations (running under some Linux system) and used this kind of code to read data from a file (in this example gas_data.dat):

void readInput(double &V, double &n, double &Tmax, double &Tmin, double &step)
{
ifstream file("gas_data.dat");

file >> V;
file >> n;
file >> Tmax;
file >> Tmin;
file >> step;

file.close();

}

This is the most simple example. But I think you get the idea. It did what I needed it to do. But on Mac OS X, it no longer works, it won't read anything... can anybody help me out?

Thanks

Basil