FairCom ISAM for C

PreviousInSet

Read the previous data record in the current key value set.

Short Name

PRVSET()

Type

ISAM function

Declaration

COUNT PreviousInSet(FILNO keyno, pVOID recptr)

Description

In V12 the file number typedef was formally changed from COUNT, a two-byte value to FILNO, a four-byte value. Refer to this link for compatibility details. Four Byte File Numbering

PreviousInSet() reads the previous data record in the set of data records whose keys match the set created by an earlier set function call. If successful, this record becomes the current ISAM record for the associated data file. If an error occurs or no previous record exists in the set, the current ISAM record is not updated, and the current key value set becomes undefined.

If the data file has variable-length records, only the fixed-length portion, defined by dreclen in the original call to CreateIFile(), is actually read into the buffer pointed to by recptr. If you wish to read the entire variable-length record into the same or a different buffer, issue a call to ReReadVRecord() after the call to PreviousInSet(). Note that ReReadVRecord() requires the size of the buffer area so that it can check if sufficient space is available.

Notice that you do not directly identify the data file number involved. The ISAM parameter file described in ISAM Functions (ISAM Database Technology, /doc/ctreeplus/30841.htm) of the c-tree 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.
118	SKEY_ERR	Either FirstInSet() has not been called or the last call to FirstInSet() was not for index number keyno.

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

Example

FILNO keyfil;

TEXT target[24],recbuf[320];

printf("\nEnter set value:");

scanf("%23s",target);

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

while (isam_err == NO_ERROR) {

process_data();

PreviousInSet(keyfil,recbuf);

}

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.