how to get number of elements in a 2d vector c++ code example

Example: initialise 2d vector in c++

// Initializing 2D vector "vect" with 
// values 
vector<vector<int> > vect{ { 1, 2, 3 }, 
                           { 4, 5, 6 }, 
                           { 7, 8, 9 } };