Commodore 1581 - Expanding a Relative File; Writing Relative File Data; Designing Relative Records

different from the equivalent line in the error check subroutine given
earlier. Here disk error number 50 is specifically ignored, because it
will be generated when the error channel is checked in line 1460. Ig
nore it because not having a requested record would only be an error
if that record had been created previously.
EXPANDING A RELATIVE FILE
If you underestimate your needs and want to expand a relative
file later, simply request the record number you need, even if it
doesn't currently exist in the file. If there is no such record yet, DOS
will create it as soon as you try to write information in it, and also
automatically create any other missing records below it in number.
When the first record beyond the current end record is written, the
DOS returns "50, RECORD NOT PRESENT" error. This is expected and
correct.
WRITING RELATIVE FILE DATA
The commands used to read and write relative file data are the
same PRINT#, INPUT#, and GET# commands used in the preceding
chapter on Sequential files. Each command is used as described there.
However, some aspects of relative file access do differ from sequential
file programming, and we will cover those differences here.
DESIGNING A RELATIVE RECORD
As stated earlier in this chapter, each relative record has a fixed
length, including all special characters. Within that fixed length, there
are two popular ways to organize various individual fields of informa
tion. One is free-format, with individual fields varying in length from
record to record, and each field separated from the next by a carriage
return character (each of which does take up one character space in
the record). The other approach is to use fixed-length fields, that may
or may not be separated by carriage returns. If fixed length fields are
not all separated by carriage returns, you will either need to be sure a
carriage return is included within each 88-character portion of the
record (88 is for BASIC 2,160 is for BASIC 7). If this is not done, you
will have to use the GET# command to read the record, at a significant
cost in speed.
Since each relative record is most easily written by a single
PRINT# statement, the recommended approach is to build a copy of
the current record in memory before writing it to disk. It can be
collected into a single string variable with the help of BASIC'S many
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