Specifying a List Entry by List Position

To designate a list entry by list position, specify the list number (LISTNUM) and the list position (LISTPOS).

List number (LISTNUM)

Designates a specific list in the list structure. The first connector to the list structure uses the LISTHEADERS parameter on the IXLCONN macro to specify the number of lists to be allocated in the list structure. List numbers in a list structure range from 0 to the LISTHEADERS value minus one.

List position (LISTPOS)

Designates the head or tail of list position. Possible values are HEAD or TAIL.

You can create a LIFO (last in, first out) or FIFO (first in, first out) queue or a stack by using LISTPOS to control how list entries are added to and removed from the list.

If there is only one list entry on the list, it is selected whether you specify LISTPOS=HEAD or LISTPOS=TAIL. Figure 1 illustrates the use of LISTPOS to reference list entries.

Figure 1. Use of List Position