How to use the positional index t[i] and t[j] well in the TSP solved by CPLEX?

[worldstar]

It is good to see the positional index of t[i] and t[j] is formulated shown in the following link.
https://github.com/alberto-santini/cplex-example/blob/master/src/solver.cpp
This positional index is able to show the sequence of each node.
Because this positional index is not used further in the model,
what if we like to use this positional index to calculate the objective function,
how could we modify the following code?
Thank you.

// Create objective function
for(auto i = 0u; i < n; ++i) {
  for(auto j = 0u; j < n; ++j) {
    expr += g.cost(i, j) * x[i][j];
  }
}