CL-Like Error Handling in RPG:

Most CL programs handle errors significantly better than RPG programs. CL handles errors better, because, it's extremely easy to trap and handle errors in CL through MONMSG. In RPG, the program and file information data structures provide error information, and the *PSSR subroutine and %STATUS built-in function can be used to trap and handle that information, but that isn't enough.

In V5R1, IBM has given RPG the capability to handle errors much the way CL does. Three new operation codes were added to RPG in V5R1 to perform kicked-up error handling: MONITOR, ON-ERROR, and ENDMON.

The MONITOR op code is used to begin error monitoring. Once the MONITOR operation is entered, the program monitors all C-specifications between it and the ENDMON operation. When a program or file exception is encountered on any statement within the monitor block, control is passed to the appropriate ON-ERROR operation, and the logic within that ON-ERROR section is performed. If all the statements within the monitor block complete successfully, control is then passed to the statement following the ENDMON operation.

The ON-ERROR operation acts much like the WHEN operation, Each ON-ERROR statement is followed by one or more statements that will execute when that specific ON-ERROR block is triggered. The block is ended when another ON-ERROR or the ENDMON statement is reached.

Any C-specifications coded after the ENDMON operation will not be trapped.

For each monitor block, at least one ON-ERROR operation must be present. The ON-ERROR operations must be coded in the same routine as the MONITOR and ENDMON operations. For example, we cannot code a MONITOR and ENDMON in the mainline and place the ON-ERROR statements in a subroutine that is called within the monitor block.