PositionSet

Establish current ISAM record as current position in set.

Short Name

MIDSET()

Type

ISAM function

Declaration

COUNT PositionSet(COUNT keyno, pVOID recptr, COUNT siglen)

Description

PositionSet extracts the key value for index keyno from the current ISAM record, and defines a set based on the first siglen bytes of this key value. This permits an application to “jump” into the middle of a set using the current ISAM record to define the set. A successful PositionSet() defines a current key value set, and subsequent calls to NextInSet() and PreviousInSet() will read the other records in the set (i.e., those records whose keys also match the first siglen bytes of keyno). If an error occurs or no key value matches the target, no key value set is defined.

Notice that you do not directly identify the data file number involved. The ISAM parameter file described in “ISAM Functions” of the c-tree Plus Programmer’s Reference Guide contains the correspondence between the index file number and the associated data file.

Return

Value	Symbolic Constant	Explanation
0	NO_ERROR	Successful retrieval of current ISAM record.
33	DNUL_ERR	recptr is NULL. No data file read performed.
42	DLOK_ERR	Could not get lock on data record. No data file read performed.
100	ICUR_ERR	No current ISAM record.
101	INOT_ERR	No active entries.

See c-tree Plus Error Codes for a complete listing of valid c-tree Plus error values.

Example

COUNT        keyfil;

TEXT         target[24],recbuf[320];


printf("\nEnter set value:");

scanf("%23s",target);


LockISAM(ctENABLE);


FirstInSet(keyfil,target,recbuf,strlen(target));


while (isam_err == NO_ERROR) {

    process_data();

    LockISAM(ctRESET);


    while (NextInSet(keyfil,recbuf) == DLOK_ERR)) {

        LockISAM(ctSUSPEND);

        PositionSet(keyfil,recbuf,strlen(target));

        LockISAM(ctRESTORE);

Limitations

No check is made to determine if recptr points to a region sufficiently large to accept a data record. If the area is too small, either code or data will be clobbered.