Variable-length and fixed-length files

The line-data transform program needs to know two things about a file in order to transform it:

  • The length of each print record
  • The kind of carriage control used
Some files contain information in each record that describes the record length; these are called variable-length files. Other files require an external definition of length; these are called fixed-length files.

For variable- and fixed-length files using length prefixes, MO:DCA–P structured fields are treated as a special case. All such structured fields are self-identifying and contain their own length. They need not contain a length prefix to be correctly interpreted but are processed correctly if there is a length prefix that matches the structured field length.