# Language Reference - Appendix

Returning Error Codes and Messages |

Often, when writing generic routines, it is desirable to not only return an error code but also an error message.

A simple technique that can be used to return an error condition and a message to a calling application is to use one of the unused system error codes. Within PxPlus, error codes are in the range from 0 to 255; however, most errors codes are below 200. For a list of all the current error codes and their meanings, see Error Codes and Messages.

To return an application error, select one of these error codes (suggest 250) and use it in an EXIT nnn directive to report an error to the user. To return an associated error message, simply issue a DEF MSG(250)="My Error Test" prior to issuing the exit, and then the programmer can use MSG(250) to determine the cause of the error. This has the added advantage that, if the error causes the system to return to Command mode, the error message will be displayed automatically.

Example:

> -:list
> 0010 ENTER TYPE$
> 0020 IF TYPE$<>"A" THEN GOTO BAD_TYPE
> 0030 ! ...
> 8000 BAD_TYPE:
> 8010 DEF MSG(250)="Unable to process Order - Wrong type"
> 8020 EXIT 250
> -:save "tstord
> C:\Pvxsrc\tstord
> ->call "tstord","B"
> Unable to process Order - Wrong type
> ->print err
> 250

This approach can be used for called sub-programs and objects.