Re: Data Overlays

[cis.ohio-state.edu!magnus.acs.ohio-state.edu!csn!news.den.mmc.com!iplmail !jcrigler@ucbvax.Berkeley.EDU (Jim Crigler)]

Bill Lee (bill@leeweyr.sccsi.com) wrote:
: In article <1993Aug13.124835.18422@iplmail.orl.mmc.com>
: rgilbert@orl.mmc.com writes:
: >
: >Many times I have wanted to create two different types to look at the
: >same object.
:
: O.k., Here's my problem:

: I have a system which receives "messages" from a number of other
: systems. The messages come via POSIX queues. On any one queue, I
: can receive a number of different messages, mostly with record
: structures defined by the C code where the message originated.

: I do not know a priori what the next message will be. I have to
: "receive" the message into a Byte_Array. Once I have the message,
: I can access a standard header and extract a message identifier,
: which then tells me what kind of message I've just received.

What about a variant record?  Language Lawyer question (my LRM is at
home):  are rep. specs allowed on variant records?  If so (and if you
have a single tag at any level that determines what the message is at
that level), use an address clause to store the data on the Byte_Array,
then use the variant to figure out what you've got.

Jim Crigler
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