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From: hotte@sunrise.in-berlin.de (Horst Laumer)
Newsgroups: comp.lang.misc
Subject: Re: Oh no! It's pointers vs arrays again!
Message-ID: <B0BM5XE@sunrise.in-berlin.de>
Date: 17 Dec 90 07:22:25 GMT
References: <2392:Nov2902:59:0590@kramden.acf.nyu.edu> <7339@lanl.gov> <184a59d8.ARN0ebd@pilhuhn.uucp> <14651@smoke.brl.mil> <11@garth.UUCP
Organization: HL EDV-Beratung
Lines: 46

userAKDU@mts.ucs.UAlberta.CA (Al Dunbar) writes:

>In article <11@garth.UUCP>, smryan@garth.UUCP (Steven Ryan) writes:
>>>has essentially only one form of data structuring, the array, while in
>>>C arrays are much less commonly used, other more appropriate data
>>>structures taking their place.  Thus, while vectorization is important
>>>.  .  .
>>
>>I infer from this that chasing pointers throughout memory is considerred
>>a better programming practice. Pointer chasing is not only good for trashing
>>the cache but for thrashing virtual memory as well.
><<<deletions>>>
>>As far as machine efficiency is concerned, pointer chasing can require
>>fewer probes, but it is sequential and accesses memory randomly and
>>unpredicatably. Memory sweeping probes every item, but it is parallel
>>(or vectorisable) and accesses memory predicatably and sequentially.
> 
>The only "randomly and unpredictably" aspects of how "pointer
>chasing" works is when someone tries to drive a C compiler
>without at least a learner's permit. Pointer operations in
>a "correct" program is completely predictable, in that the
>results achieved are correct. If you are concerned with the
>fact that the values of the actual addresses used in pointers
>is difficult to determine from reading the code, you may have
>missed the whole point of "abstraction". The address values
>are a detail that, like hexadecimal arithmetic, you can
>usually forget about.
> 

Right, my dear!

C ain't PASCAL, where "address of object X" may not be the same
as "pointer to object X".

(BTW, in another article, I saw the question "how to PEEK() and
POKE() in C....". Horrible imagination!)

Suggestion: try to understand the man-page of qsort(3) or something
like that!

--HL
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