| Re: compile a routine wich inlude a commun [message #47124 is a reply to message #47067] |
Tue, 24 January 2006 08:09   |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Peter Albert wrote:
>> No, it does not. Whether or not you point to the "complete" variable, or just a part of
>> it, a new heap "variable" is created.
>>
>> IDL> x=indgen(4,4)
>> IDL> print, x
>> 0 1 2 3
>> 4 5 6 7
>> 8 9 10 11
>> 12 13 14 15
>> IDL> p=ptr_new(x)
>> IDL> print, *p
>> 0 1 2 3
>> 4 5 6 7
>> 8 9 10 11
>> 12 13 14 15
>> IDL> print, (*p)[1:2,1:2]
>> 5 6
>> 9 10
>> IDL> (*p)[1:2,1:2] = (*p)[1:2,1:2] + 100
>> IDL> print, *p
>> 0 1 2 3
>> 4 105 106 7
>> 8 109 110 11
>> 12 13 14 15
>> IDL> print, x
>> 0 1 2 3
>> 4 5 6 7
>> 8 9 10 11
>> 12 13 14 15
>
>
> Damn, I should have tried it before. I was so sure :-(
>
> But then, this _is_ a polite group. Nobody murmuring something like
> rtfm, while a look in the manual reveals :
>
> "If InitExpr is provided, PTR_NEW uses it to initialize the newly
> created heap variable. Note that the new heap variable does not point
> at the InitExpr variable in any sense-the new heap variable simply
> contains a copy of its value."
>
> Well, here is is, black on white. So you _can't_ alias variables or
> subarrays.
Huh, how 'bout that? It's in the manual. (ehem)
I wonder why RSI decided to implement pointers this way? Or, to rephrase, why they called
the implementation they chose a pointer?
paulv
--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC
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