Split a string into fixed-length parts.
linesplit.fixed(
cline,
length_per_part,
num_parts_expected = NULL,
error_tag = NULL
)
character string, the input line
integer, number of characters per part
integer, the number of parts. Leave at NULL if this is not known.
optional character string, how to identify the line in a parsing error message. Could be the line number, or whatever. Only relevant if 'num_parts_expected' is not matched.