Example 1: SHOWCB macro (display an access method control block)

In this example, a SHOWCB macro is used to display fields in an access method control block. The fields displayed (KEYLEN, LRECL, and RKP) permit the program to modify variables to process any one of many data sets that have different sized key fields and records and different placements of key field in a record.

        SHOWCB ACB=CONTROL,                                           x
               AREA=DISPLAY,                                          x
               FIELDS=(KEYLEN,                                        x
               LRECL,RKP),                                            x
               LENGTH=12
 
DISPLAY DS     0F               Align on fullword boundary.
KEYLEN  DS     F
LRECL   DS     F
RKP     DS     F

The SHOWCB macro's parameters are:

• ACB specifies the address of the access method control block to be displayed.
• AREA specifies the area used to display access method control block fields begins on a fullword boundary.
• FIELDS specifies the KEYLEN, LRECL, and RKP fields are displayed.
• LENGTH specifies the length of the area used for the display is 12 bytes, enough to accommodate the specified fields.