If Var1 is a string variable in your table, then because you're assigning a string "buf" to it, maybe you need
grnd_truth_table(1, "Var1") = buf; % Maybe {} instead of ()???
You forgot to attach 'ground_truth.txt' so I can't really try anything for you. Good luck though.
Can you even do this:
grnd_truth_table.Var1(i)
when you try sprintf() or does that bomb?
