What do you mean that you can't save strings ?
Can you remove everything else that is not needed.
If you want to read a string before a comma, then there must be something to read.
A zero-terminated string has a byte at the end that is zero.
That means the string "Hi" is three bytes. The string "Sketch" is 7 bytes.
If you make an array for the text "Sketch", then make it 20, 30 or 40 bytes.