| Re: nested structures [message #84441 is a reply to message #52210] |
Tue, 28 May 2013 00:28   |
hannah_ue
Messages: 14
Registered: November 2012
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Junior Member |
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Thank you Phillip, that helped. I finally figured out (I hope) how to reference to the array of structures in the array of structures and how to replicate those independently. I think I'm getting on now.
Am Montag, 27. Mai 2013 17:03:01 UTC+2 schrieb Phillip Bitzer:
> You can certainly do what you're after. In fact, I do this sort of thing when building arrays of radar data, which may have different lengths, sizes, etc.
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> First, some basic pointer stuff:
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> Consider:
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> IDL> s1 = {tag1:0L, tag2:PTR_NEW(/ALLOCATE)}
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> Then,
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> IDL> help, s1
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> ** Structure <314b91d8>, 2 tags, length=8, data length=8, refs=1:
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> TAG1 LONG 0
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> TAG2 POINTER <PtrHeapVar14>
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> So, we see tag2 is a pointer. Fine, let's assign the pointer to a (new) structure:
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> IDL> *s1.tag2 = {ntag1:0L, nTag2:0L}
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> Okey doke. So, s1.tag2 is the pointer, and when we dereference this:
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> IDL> help, *s1.tag2
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> ** Structure <1dc84338>, 2 tags, length=8, data length=8, refs=1:
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> NTAG1 LONG 0
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> NTAG2 LONG 0
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> we see our (new) structure.
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> What about getting to one of these tags? Notice this doesn't work:
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> IDL> help, *s1.tag2.ntag2
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> % Expression must be a structure in this context: <No name>.
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> % Execution halted at: $MAIN$
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> But this does:
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> IDL> help, (*s1.tag2).ntag2
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> <Expression> LONG = 0
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> Remember, *s1.tag2 is the pointer, and that's what what we want to dereference. That's why the parentheses are where they are.
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> Arrays of structures with pointers can be a little more tricky, because you'll be throwing brackets in there too. Just keep in mind where the pointer is.
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> Further, you'll want to take a look a this for the initialization:
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> http://www.idlcoyote.com/code_tips/structptrinit.html
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