| Re: A simple DLM question [message #81227 is a reply to message #81224] |
Tue, 28 August 2012 14:16   |
Xin Tao
Messages: 40
Registered: April 2011
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Member |
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I did check the flags of IDL_V_CONST and IDL_V_TEMP. Both failed, and then I posted the question. For example, I'm not sure how to explain this results.
// Code here.
void simple(int argc, IDL_VPTR argv[])
{
IDL_VPTR v;
v = IDL_BasicTypeConversion(1, &argv[0], IDL_TYP_DOUBLE);
printf("const = %d\n", v->flags & IDL_V_CONST);
printf("temp = %d\n", v->flags & IDL_V_TEMP);
if (v != argv[0]) IDL_DELTMP(v);
}
Now results:
IDL> simple, 3.0d
const = 1
temp = 0
IDL> simple, -3.0d
const = 0
temp = 2
This sounds really strange to me. But if there is a good explanation of this, please let me know. Thanks.
Xin Tao
On Tuesday, August 28, 2012 11:06:44 AM UTC-5, jimmylee...@gmail.com wrote:
> On Monday, August 27, 2012 4:04:43 PM UTC-6, Xin Tao wrote:
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>> Thanks Jimmy. That indeed solved my problem. It was so confusing to me, because I found from the External Development Guide that IDL_DELTMP should check it first. :)
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>> On Monday, August 27, 2012 3:48:27 PM UTC-5, jimmylee...@gmail.com wrote:
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>>> On Monday, August 27, 2012 11:13:57 AM UTC-6, Xin Tao wrote:
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>>>> Hi,
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>>>> I'm having trouble figuring out the problem of the following DLM code:
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>>>> /* The c routine */
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>>>> void simple(int argc, IDL_VPTR argv[])
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>>>> {
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>>>> IDL_VPTR v;
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>>>> v = IDL_BasicTypeConversion(1, &argv[0], IDL_TYP_DOUBLE);
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>>>> IDL_DELTMP(v);
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>>>> }
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>>>> This routine just takes its input and convert it to double. After converting it to a DLM, however, I seem to see strange results.
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>>>> IDL> simple, 1.0d
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>>>> % Loaded DLM: TESTMODULE.
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>>>> IDL> simple, -1.0d
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>>>> Bus error
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>>>> That is: if I give it 1.0d as input, then the code is fine. However, if I use -1.0d, then there is a BUS error, presumably from IDL_DELTMP(v). I really don't understand why this is the case. Isn't IDL_DELTMP supposed to decide first whether v is a temporary variable or not? If I remove IDL_DELTMP, of course, I'll frequently get the annoying warning message "% Temporary variables are still checked out - cleaning up...".
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>>>> Please give me some help. Thanks.
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>>> Try this:
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>>> if (v != argv[0]) IDL_DELTMP(v);
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>>> That is, no conversion was necessary.
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>>> 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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> The docs are correct, but are confusing if you're not aware of the difference between IDL's temporary variables, constants, and named variables. It's not stated explicitly in this section that a constant like 1.0D is a different sort of data type internally than an expression or named variable, though that topic is discussed earlier in the docs.
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> IDL_DELTMP doesn't check if the IDL_VARIABLE has the contant flag set (IDL_V_CONST), only the temporary flag (IDL_V_TEMP).
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> As a matter of habit, I always check the equality of the argv[] used as input against the output from any type conversion routine call before calling IDL_DELTMP. You can't predict when a user has entered an explicit constant value, rather than a variable name or expression.
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