"Clark Morris" <cfmpub...@ns.sympatico.ca> wrote in message news:<vp8je5lglad10009vdssa42f02ssit0...@4ax.com>... > On 29 Oct 2009 03:17:25 -0700, in bit.listserv.ibm-main you wrote: > > >>How can new programs determine if they received the new or the old > >>format, i.o.w. if they can/should process the data after byte 100 or not? > > > >It's really quite simple Kees, the program should process exactly the
> >number of bytes that the 2-byte (halfword) length prefix says is > >present, no more and no less. This has been the case for > 40 years. > > Back in the dark ages when I was programming, I checked the parm > length field to be sure that it was values that I was expecting (zero > being just one of the values). I would never have considered just > using the Parm length field to determine the size of a move to a work > area. I also would not have used an arbitrary size value for any > operation on the parm field since the parm could be either missing or > shorter than expected. Either case could cause mysterious things to > happen. Since my recollection of the size field being a halfword > seems to be correct, then what is the problem with a parm field over > 100 bytes since any using program should be testing the size and > making sure that any overwrite isn't occurring anyway (or that an > overly short field isn't being passed)? This is not fully failsafe: the parm was documented as being limited to 100 bytes. So easy programmering could initialize a 100 byte area to blanks and move the parmdata into it, using the length field, which *never* could exceed 100 bytes. Allowing over 100 bytes lengths will compromise downward compatibility. Kees. ********************************************************************** For information, services and offers, please visit our web site: http://www.klm.com. This e-mail and any attachment may contain confidential and privileged material intended for the addressee only. If you are not the addressee, you are notified that no part of the e-mail or any attachment may be disclosed, copied or distributed, and that any other action related to this e-mail or attachment is strictly prohibited, and may be unlawful. If you have received this e-mail by error, please notify the sender immediately by return e-mail, and delete this message. Koninklijke Luchtvaart Maatschappij NV (KLM), its subsidiaries and/or its employees shall not be liable for the incorrect or incomplete transmission of this e-mail or any attachments, nor responsible for any delay in receipt. Koninklijke Luchtvaart Maatschappij N.V. (also known as KLM Royal Dutch Airlines) is registered in Amstelveen, The Netherlands, with registered number 33014286 ********************************************************************** ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
