Using KSAM/XL and KSAM 64 (32650-90886)

52 Chapter5

Reading File Data

Random Access of a Single Record

A record can be accessed randomly by a particular key value or by its relative or physical

record number.

Using a Key Value

The FREADBYKEY intrinsic is recommended for retrieving records randomly. The desired

key value

and the

key location

are speciﬁed in the intrinsic parameters. The index of

the speciﬁed key is checked for a matching key value and the appropriate record is read.

If an exact key value match is not found, an error condition is returned. Because of this,

the FREADBYKEY intrinsic is not appropriate when searching for an approximate key value

or the lowest value of a key. Use the FFINDBYKEY intrinsic in such cases.

Figure 5-4. Accessing a Record by Key Value

target := ’ ’;

tcount := -8;

keyvalue := ’15 ’;

keylocation := 5;

lgth :=FREADBYKEY(filenum,target,tcount,keyvalue,keylocation);

Using the Relative Record Number

Records can also be accessed randomly using the FFINDN intrinsic. To use this intrinsic,

however, you need to know the record's relative record number in its key sequence.

Using a Physical Record Number

The FREADDIR intrinsic reads a single record based on its physical record number in the

ﬁle. The record number is supplied as parameter data in the intrinsic call. Record

numbering starts with either 1 or 0, depending on the speciﬁcations made when the ﬁle

was built.

The FPOINT and FREADC intrinsics can be used to read a record based on its physical record

number. The FPOINT intrinsic positions the pointers to the record identiﬁed by its physical

record number in the ﬁle. The FREADC intrinsic is then used to read the record based on the

physical record pointer without reference to the record's index location.

In this case, the FREAD intrinsic could also be used to read the record, because the FPOINT

intrinsic also sets the logical record pointer to the record that it located by physical record

number. By default, the key used is the primary key for that record. An alternate key is

used, however, if such a key was speciﬁed by a previous call to the FFINDBYKEY or

FREADBYKEY intrinsic.

NOTE

This is true for the reads on the previous examples of FFINDN FFINDBYKEY,

FREADBYKEY intrinsics that sets the key of reference for succeeding reads.