File Management - IBM

38 File Management V4R5
The following topics provide additional information about how overrides work on
AS/400 and how they affect and are affected by different events:
v “How the system processes overrides” on page 40
v “Effect of exits on overrides: scenario” on page 48
v “Effect of TFRCTL on overrides-Scenario” on page 49
v “Overrides to the same file at the same call level: scenario 1” on page 49
v “Overrides to the same file at the same call level: scenario 2” on page 49
v “CL program overrides” on page 50
v “Securing files against overrides” on page 51
v “Using a generic override for printer files” on page 51
v “Applying overrides when compiling a program” on page 53
Overriding file attributes
The simplest form of overriding a file is to override some attributes of the file. File
attributes are built as a result of the following:
v Create file and add member commands. Initially, these commands build the file
attributes.
v Program using the files. At compile time, the user program can specify some of
the file attributes. (The attributes that you can specify depend on the high-level
language in which the program is written.)
v Override commands. At the time when a program runs, these commands can
override the file attributes previously built by the merging of the file description
and the file parameters specified in the user program.
For example, assume that you create a printer file OUTPUT whose attributes are:
v Page size of 60 by 80
v Six lines per inch
v Two copies of printed output
v Two pages for file separators
v Overflow line number of 55
The Create Printer File (CRTPRTF) command looks like this:
CRTPRTF FILE(QGPL/OUTPUT) SPOOL(*YES) +
PAGESIZE(60 80) LPI(6) COPIES(2) +
FILESEP(2) OVRFLW(55)
You specify the printer file OUTPUT in your application program with an overflow
line number of 58 and a page size of 66 by 132.
However, before you run the application program, you want to change the number
of printed copies to 3, and the overflow line to 60. The override command looks
like this:
OVRPRTF FILE(OUTPUT) COPIES(3) OVRFLW(60)
Then you call the application program, and three copies of the output print.
When the application program opens the OUTPUT file, the system merges the
file-specified attributes, program-specified attributes, and override-specified
attributes to form the open data path. The system uses the open data path when
the program runs. The system merges file-specified overrides with the
program-specified attributes first. Then it merges these merged attributes with the