Open System Services System Calls Reference Manual (G06.28+, H06.05+)

SPT_READX(2) OSS System Calls Reference Manual
Transfer sizes over 4 KB are not supported in default mode for unstruc-
tured access to structured files.
Large data transfers using SPT_SETMODE(141)
For SPT_READX( ) only, large data transfers (more than 4096 bytes)
can be done for unstructured access to structured or unstructured files,
regardless of unstructured buffer size, by using SPT_SETMODE()
function 141. When you use SPT_SETMODE(141) to enable large data
transfers, you can specify up to 56K (57344) bytes for the read_count
parameter. For an explanation of function 141, see the Guardian SET-
MODE procedure description in the Guardian Procedure Calls Refer-
ence Manual.
Structured files
A subset of records for sequential SPT_READX() calls
The subset of records read by a series of calls to
SPT_READX( ) is specified through calls to the Guar-
dian POSITION or KEYPOSITION procedures.
Reading of an approximate subset of records
If an approximate subset is being read, the first record
returned is the one whose key field, as indicated by the
current key specifier, contains a value equal to or greater
than the current key. Subsequent reading of the subset
returns successive records until the last record in the file
is read (an EOF indication is then returned).
Reading of a generic subset of records
If a generic subset is being read, the first record returned
is the one whose key field, as designated by the current-
key specifier, contains a value equal to the current key
for comparison-length bytes. Subsequent reading of the
file returns successive records whose key matches the
current key (for comparison-length bytes). When the
current key no longer matches, an EOF indication
returns.
For relative and entry-sequenced files, a generic subset
of the primary key is equivalent to an exact subset.
Reading of an exact subset of records
If an exact subset is being read, the only records
returned are those whose key field, as designated by the
current-key specifier, contains a value of exactly the
comparison length bytes (see the Guardian KEYPOSI-
TION procedure in the Guardian Procedure Calls
Reference Manual) and is equal to the key. When the
current key no longer matches, an EOF indication
returns. The exact subset for a key field having a unique
value is at most one record.
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