Re: TR : Helton article Throw/Catch -- RPG400-L

Hi Paul,

I was just wondering what you meant by
 "on-error catches all message IDs.  In fact, that's the problem
 with it!  it doesn't give you a change to specify that some of them are
 "unhandled",

As you, yourself, pointed out, on-error will catch everything. It notonly will catch the messages that you send with the throw() subprocedure,but it'll also catch an MCH1202 or some other error that you may not haveexpected.

For example, let's say I'm writing a subprocedure to delete a file. Thecaller might expect that the file doesn't exist, so it might want tomonitor for CPF1205, and if that's the only error that gets thrown,continue normally.

On the other hand, if something totally unexpected occurs, for example anMCH3601, I might want NOT want to catch it. OR I might want to let anotherprogram that's higher up on teh call stack decide whether or not it shouldhandle the error.

You can do that easily in CL with the MONMSG command, but it's not so easyin RPG, because you can't monitor for specific msgid's, only for RPGstatus codes.

When you find an exception like this that you DON'T want to handle (butwould prefer the OS's error handler to kick in) then what you have to doin RPG (because there isn't a better alternative) is send a new *ESCAPEmessage.

Because the procedure that you called can return ANY escape message, theeasiest way to handle these "unexpected exceptions" is to use the QMHRSNEMAPI. That API will look up the last exception that occurred, and it'llre-send it to your caller.

That way, when the MCH3601 occurs in a subprocedure that I called, I callQMHRSNEM and the exact same MCH3601 message gets sent to my caller. It'svery much like the way ILE would've propagated the error message up thecall stack if I had not caught the error.

I posted an example of the QMHRSNEM API to this mailing list in the past.Here's the link to where I posted that example:

http://archive.midrange.com/rpg400-l/200510/msg00610.html

I hope this explanation was better.