Open System Services System Calls Reference Manual (G06.28+)

SPT_WRITEX(2) OSS System Calls Reference Manual
DP2 performance with unstructured files is best
when requested transfers begin on BUFFER-
SIZE boundaries and are integral multiples of
BUFFERSIZE.
If the SPT_WRITEX() call is to an unstruc-
tured disk file, data is transferred to the record
location specified by the next-record pointer.
The next-record pointer is updated to point to
the record following the record written.
Number of bytes written
If an unstructured file is created with the odd
unstructured attribute (also known as
ODDUNSTR) set, the number of bytes written is
exactly the number specified in write_count.If
the odd unstructured attribute is not set when the
file is created, the value of write_count is
rounded up to an even value before the
SPT_WRITEX() is executed.
You set the odd unstructured attribute with the
Guardian FILE_CREATE_,
FILE_CREATELIST_, or CREATE procedure,
or with the File Utility Program (FUP) SET and
CREATE commands.
File pointers after an SPT_WRITEX() call
After a successful SPT_WRITEX() call to an
unstructured file, the file pointers have these
values:
• current-record pointer is the next-record
pointer
• next-record pointer is the next-record
pointer plus the count written
• end-of-file (EOF) pointer is the max-
imum of the EOF pointer or the next-
record pointer
Use on files opened for nowait I/O
• If the buffer is in an extended data seg-
ment, you cannot deallocate or reduce
the size of the extended data segment
before the I/O completes with a call to
the Guardian AWAITIOX procedure or
is canceled by a call to the
SPT_CANCEL() function or the Guar-
dian CANCELREQ procedure.
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