| Re: read a C written binary file with IDL [message #79335 is a reply to message #79238] |
Mon, 20 February 2012 19:43  |
manodeep@gmail.com
Messages: 33
Registered: June 2006
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Member |
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On Feb 20, 7:49 pm, bing999 <thibaultga...@gmail.com> wrote:
> Hi,
>
> sorry to reply so late, but I was away recently.
>
> First, as the issue seems to be more complicated than i first thought,
> i have to say that the structure i have to read is bigger than what I
> wrote previously just to make an example.
>
> It actually contains (in the right order):
> int x 1
> long long x 1
> int x 5
> float x 9
> int x 1
> float x 24
>
> that is, 7 int, 33 float and 1 long long (written in C).
>
> When I look at the IDL commands you suggest, i get:
>
> print,n_tags(mystruct,/length) 176
>
> print,n_tags(mystruct,/data_length) 172
>
> So you were right.
>
> Now, the question is "How to handle that?? " :)
>
> I inserted an extra int (0L) in the structure of my IDL reading
> routine in second position of the structure (just before the long
> long), and it gives results coherent with what one gets with a correct
> Python routine. However, I am not quite satisfied with this
> solution...
>
> Does anyone can think of a better way to proceed?
>
> Thanks !!
>
>
>
>
>
>
>
>
>
>> Bill Nel wrote:
>>> On Feb 9, 11:56 pm, Manodeep Sinha <manod...@gmail.com> wrote:
>>>> Hi,
>
>>>> This is because C pads the structure to produce alignments. Under
>>>> 'normal' operations, you would expect MyStruct to be 20 bytes,
>>>> however, if you do a sizeof(struct MyStruct), you will probably see
>>>> that the size is 24. (And you can enable the warning for gcc by using
>>>> the compile time option -Wpadded).
>
>>> The N_TAGS() function has LENGTH and DATA_LENGTH keywords:
>
>>> IDL> print, n_tags(mystruct, /length)
>>> 24
>>> IDL> print, n_tags(mystruct, /data_length)
>>> 20
>
>>> I mention it because one might not think to look at the N_TAGS
>>> function
>>> for this sort of information.
>
>>> --Wayne
As Paul suggested, you should check out the assoc function. I can read
the data in just fine through IDL:
---------------
openu, 1, 'data.bin', /SWAP_IF_BIG_ENDIAN
a = assoc(1, {a:0L, b:0LL, c:lonarr(5),d:fltarr(9),e:0L,f:fltarr(24)})
print,a[0]
--------------
Cheers,
Manodeep
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