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Methods for Processing Disk Files
*****************************************************************
* PROGRAM NAME: ESWLIM2 *
* RELATED FILES: EMPMST (Physical File) *
* LIMITS (Physical File) *
* PRINT (Printer File) *
* DESCRIPTION: This program shows the processing of an *
* externally described file sequentially *
* within limits. *
* This program prints out information for the *
* employees whose employee numbers are within *
* the limits given in the file LIMITS. *
*****************************************************************
FLIMITS IR F 6 3 DISK RAFDATA(EMPMST)
FEMPMST IP E L K DISK
FPRINT O F 80 PRINTER
* Input Specifications are optional for an externally described
* file. Here, *IN01 is defined as the record-identifying
* indicator for the record-format EMPREC to control the
* processing of this record.
IEMPREC 01
OPRINT H 1P 1
O 12 'SERIAL #'
O 22 'NAME'
O 45 'DEPT'
O 56 'TYPE'
O D01 1
O ENUM 10
O ENAME 35
O EDEPT 45
O ETYPE 55
O*
Figure 154. Sequential-within-Limits Processing of a Program-Described File
Relative-Record-Number Processing
Random input or update processing by relative record number applies to full proce-
dural files only. The desired record is accessed by the CHAIN operation code.
Relative record numbers identify the positions of the records relative to the begin-
ning of the file. For example, the relative record numbers of the first, fifth, and
seventh records are 1, 5, and 7, respectively.
For an externally described file, input or update processing by relative record
number is determined by a blank in position 34 of the file description specifications
and the use of the CHAIN operation code. Output processing by relative record
number is determined by a blank in position 34 and the use of the RECNO keyword
on the file description specification line for the file.
Use the RECNO keyword on a file description specifications to specify a numeric
field that contains the relative record number that specifies where a new record is
to be added to this file. The RECNO field must be defined as numeric with zero
decimal positions. The field length must be large enough to contain the largest
record number for the file. A RECNO field must be specified if new records are to
be placed in the file by using output specifications or a WRITE operation.
Chapter 16. Accessing Database Files 303