Opening a file (ESDS, KSDS, or RRDS)
Before you can use WRITE, START, READ, REWRITE,
or DELETE statements to process records in a file,
you must first open the file with an OPEN statement.
Whether a file is
available or optional affects OPEN processing, file
creation, and the resulting file status key. For example, if you open
in EXTEND, I-O, or INPUT mode
a nonexistent non-OPTIONAL file, the result is an OPEN error,
and file status 35 is returned. If the file is OPTIONAL,
however, the same OPEN statement returns file status
05, and, for open modes EXTEND and I-O,
creates the file.
An OPEN operation works
successfully only if you set fixed file attributes in the DD statement
or data-set label for a file, and specify consistent attributes for
the file in the SELECT clause and FD entries
of your COBOL program. Mismatches
in the following items result in a file status key 39 and the failure
of the OPEN statement:
- Attributes for file organization (sequential, relative, or indexed)
- Prime record key
- Alternate record keys
- Maximum record size
- Record type (fixed or variable)
How you code the OPEN statement for
a VSAM file depends on whether the file is empty (a file that has
never contained records) or loaded. For either type of file, your
program should check the file status key after each OPEN statement.