How to randomly pick element from an array with different probabilities in C++

Suppose I have a vector<Point> p of some objects.

I can pick a uniformly random by simply p[rand() % p.size()].

Now suppose I have another same-sized vector of doubles vector <double> chances.

I want to randomly sample from p with each element having a probability analogous to its value in chances (which may not be summing to 1.0). How can I achieve that in C++?