gtk:text-iter-line (iter)

iter -- a gtk:text-iter instance
line -- an integer with the line number, counted from 0

The gtk:text-iter-line function returns the line number containing the iterator. The (setf gtk:text-iter-line) function moves the iterator to the start of the given line number.

Lines in a text buffer are numbered beginning with 0 for the first line in the text buffer. If the given line number is negative or larger than the number of lines in the text buffer, moves the iterator to the start of the last line in the text buffer.