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Re: A simple DLM question [message #81217 is a reply to message #81216]

Wed, 29 August 2012 09:23

Xin Tao
Messages: 40
Registered: April 2011

Member

That's very clear explanation, thanks. But I would still say that it's not very intuitive to me that 3 is a constant but -3 is not.

On Wednesday, August 29, 2012 10:55:28 AM UTC-5, Chris Torrence wrote:
> Hi all,
>
>
>
> Just to clarify, this isn't a bug. It just happens that since the minus sign is an operator, then a number such as -1 gets turned into an expression, which is stored in a temporary variable. It is treated the same way as say "-a" where "a" is a variable.
>
>
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> Jimmy said "The macro (in idl_export.h, if you're interested) doesn't do extensive checking, and you should only free variables that are temps, not expressions or constants."
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> That isn't quite correct. In this particular case, you *must* check (v != argv[0]), regardless of whether it is a constant or temp variable. That is because if the type conversion was not needed, then "v" will be equal to argv[0]. In this case, your code does not "own" argv[0] since it didn't allocate it. Freeing "v" is bad in that case, because IDL will attempt to free it later, and a double free will occur.
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> Probably the best way to write the line of code is:
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> if (v != argv[0]) IDL_Deltmp(v);
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> Here, you don't need to use the macro, because you *know* that if "v" is not equal, then it must be a temporary that is owned by you, and you can free it without doing any further checks.
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> Hope this helps.
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>
>
> -Chris
>
> ExelisVIS

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[Message index]

		Re: A simple DLM question By: Michael Galloy on Wed, 29 August 2012 11:16
		Re: A simple DLM question By: chris_torrence@NOSPAM on Wed, 29 August 2012 10:50
		Re: A simple DLM question By: Lajos Foldy on Wed, 29 August 2012 10:31
		Re: A simple DLM question By: Xin Tao on Wed, 29 August 2012 09:23
		Re: A simple DLM question By: chris_torrence@NOSPAM on Wed, 29 August 2012 08:55
		Re: A simple DLM question By: Xin Tao on Tue, 28 August 2012 22:03
		Re: A simple DLM question By: Craig Markwardt on Tue, 28 August 2012 18:10
		Re: A simple DLM question By: Xin Tao on Tue, 28 August 2012 14:16
		Re: A simple DLM question By: Jim Pendleton on Tue, 28 August 2012 09:06
		Re: A simple DLM question By: Xin Tao on Mon, 27 August 2012 15:08
		Re: A simple DLM question By: Xin Tao on Mon, 27 August 2012 15:04
		Re: A simple DLM question By: Craig Markwardt on Mon, 27 August 2012 13:51
		Re: A simple DLM question By: Jim Pendleton on Mon, 27 August 2012 13:48

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