Modifying fields in the command-level parameter structure by exits XPCREQ, XPCERES, and XPCREQC

Some fields that are passed to program control are used as input to the request, some are used as output fields, and some are used for both input and output. The method your user exit program uses to modify a field depends on the usage of the field.

Modifying input fields

The correct method of modifying an input field is to create a new copy of it, and to change the address in the command parameter list to point to your new data.

Note: You must never modify an input field by altering the data that is pointed to by the command parameter list. To do so would corrupt storage belonging to the application program and could cause a failure when the program attempted to reuse the field.

Modifying output fields

The technique described in Modifying input fields is not suitable for modifying output fields. (The results would be returned to the new area instead of the application’s area, and would be invisible to the application.)

An output field is modified by altering the data that is pointed to by the command-level parameter list. In the case of an output field you can modify the application’s data in place, because the application is expecting the field to be modified anyway.