Control Data Corporation 3300 Reference Manual page 153

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The USE procedures in format I . . are executed by the input-output control
system after completion of the standard input-output error routine.
If
a bad block is read, the error declarative is executed for each READ
statement that causes retrieval of a logical record from the bad block.
On
entry to the declarative, the record requested will have been moved to
the record area. Upon exiting the declarative, the input-output control
system ignores the error, accepts the bad record, and resumes normal
processing.
If a WRITE error occurs, the declarative is executed only once for the error.
In
format 2 for an input file, the procedures are executed before and/or
after execution of a beginning or ending input label check procedure. For an
output file, the USE procedures are executed either before a beginning or
ending output label is created, or after a beginning or ending output label is
created but before it is written on tape.
The following rules govern format 2 USE procedures:
If
file-name-I, file-name-2, etc. is specified, the associated File
Description entry for the file must not specify LABEL RECORDS ARE
OMITTED.
If
the words BEGINNING or ENDING are not included, the designated
procedures are executed for both beginning and ending labels.
If neither REEL nor FILE is included, the designated procedures are
executed for both REEL and FILE labels. The REEL option is not
applicable to mass storage files.
The USE label procedures are not applicable to scratch files. The USE label
procedure statement may be used for mass storage files even though mass
storage file labels are maintained by MASTER and are not available to the
user. Only the BEFORE or AFTER BEGINNING FILE or UNIT options of
format 2 are valid. The UNIT and FILE options are synonymous. The
input-outplt control system passes control to the BEFORE BEGINNING
procedure just before the user's label identification data is moved to a
MASTER OPEN request skeleton. The MASTER OPEN request makes the
file available for processing, and then control passes to the AFTER BE-
GINNING label procedure.
USE BEFORE REPORTING (format 3) is used only in conjunction with the
Report Writer.
It
is described in section 5.4.4 with the Report Writer
statements.
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