Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!world!decwrl!sgi!zok!wattres!steve
From: steve@wattres.uucp (Steve Watt)
Newsgroups: comp.lang.c
Subject: Re: Mixing types in arrays
Summary: Use a struct...  if not that, then watch for RISC systems.
Message-ID: <1991Feb15.053223.813@wattres.uucp>
Date: 15 Feb 91 05:32:23 GMT
References: <22040@hydra.gatech.EDU>
Reply-To: steve@wattres.UUCP (Steve Watt)
Organization: Steven Watt, Consultant
Lines: 34

In article <22040@hydra.gatech.EDU> cc100aa@prism.gatech.EDU (Ray Spalding) writes:
>I keep finding myself wanting to store shorts and longs (as well as
>chars) in arrays of char, such as in the following simple example.
[ stuff deleted ]
>But, are there other pitfalls?  Systems on which this won't work?  A
>better way?

One system that this won't work on is the IBM RT (at least under AIX), because
a non-aligned integer (read 32 bit) access will get *garbage* in various places.
It will produce 'fixed up unaligned access at xxxxxxxxx for pid xxxx' on the
DECStation, unless the message is turned off, and will probably blow in strange
and subtle ways on other RISC systems.

A better way?  Use a struct?  Probably not as compact, but *much* more obvious.

For example, the code (left to the reader) for the following definitions could
do (mostly) the same thing, but the search (even linear!) is quite a bit
quicker, since it isn't calling strlen all the time.

    typedef struct {
      long value;
      char key[1];
    } item;

    item *data[1000];

Yes, you have to malloc a copy every time, but that's not so bad.  But you
can easily play all of the various data structure optimization games from
here (binary searches with ordered list, etc...)
Have fun!
-- 
Steve Watt
...!claris!wattres!steve		wattres!steve@claris.com also works
Never trust a computer bigger than you can lift.