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Re: pointer to structures [message #19541 is a reply to message #19540]

Wed, 05 April 2000 00:00

Liam E. Gumley
Messages: 378
Registered: January 2000

Senior Member

"J.D. Smith" wrote:
>
> "Liam E.Gumley" wrote:
>>
>> "J.D. Smith" wrote:
>>> With time, you will get used to these semantics. They seem arcane, but
>>> eventually it becomes somewhat readable to the experienced eye. Of course, I've
>>> struggled with statements like:
>>>
>>> HEADER=*(*(*self.DR)[sel[i]].HEADER)
>>
>> I neglected to provide an example of why simplified pointer and
>> structure referencing is desirable. Thanks for the help JD!
>>
>> ;-)
>>
>> Cheers,
>> Liam.
>
> But then you have to ask yourself which is worse, the confusing string above, or
> the explicit:
>
> drs_ptr=self.DR
> drs=*drs_ptr
> this=drs[sel[i]]
> hd_arr_ptr=*this
> hd=*hd_arr_ptr
>
> repeat this about 5000 times throughout your application, and you begin to
> appreciate the terse form above. Especially if you're passing some part of the
> nested data to a routine by reference... intermediate variables require you to
> remember to assign them after use (everybody remember
> widget_control,stash,set_uvalue=state,/NO_COPY?).

I would not repeat this code 5000 times. I'd find a way to encapsulate
it in a function where I can include comments and error checking (e.g.
Is this a valid pointer? Does it point to a defined variable?). In these
cases I find it much better to create a 'put' and 'get' function pair
where all the de-referencing is handled inside the function. That way I
can use the 'put' and 'get' modules all over the place, and if I change
the way the pointers/structures are nested, I only have to change the
code in two places (inside the functions).

Cheers,
Liam.

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[Message index]

		Re: pointer to structures By: John-David T. Smith on Wed, 05 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Wed, 05 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Tue, 04 April 2000 00:00
		Re: pointer to structures By: davidf on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Ben Tupper on Tue, 04 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: davidf on Tue, 04 April 2000 00:00
		Re: pointer to structures By: wbiagiot on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Ben Tupper on Tue, 04 April 2000 00:00

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