Type III C lass A Program

RDBUF Macro
Purpose:
RDBUF reads a record from a disk file.
Format:
label
fcb
alabel
elabel
Usage:
I I RDBUF I fcb I
is an optional statement label
is the lahel of the FCB naming the file to be read
is the label of an input buffer. If omitted, the
area specified in the FeB is used
is the entry of
omitted, errors,
ignored.
an error-handling routine.
including end of file,
If
are
RDBUF returns one item each time it is executed. The item
returned is specified by the item number field of the File
Control Block at FCB+26. This number is incremented each
time RDBUF is executed. It may be set to any value,
allowing direct access to files.
The file read may have fixed or variable length records i • but
the buffer named AREA= must be large enough for the longest
record in the file. The buffer named with RDBUF overrides
that specified in FCB if it is different.
Each time RDBUF is executed, it links via a CMS SVC
instruction to a routine that returns control when the
record requested bas been read in. If no error occurs,
register 15 is set to zero on return. If an error or end of
file occurs, register 15 contains a code indicating the type
of error,. See Figure 21 for a list of RDBUF error returns.
If ERROR1 is supplied, control goes to that point on an
error. If no label is supplied, control returns immediately
following RDBUF. regardless of error.. Note that end of file
is always consid'ered an error. An error handling routine
should start with the CREOF macro, to detect end of file ..
284 RDBUF Macro