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Re: read a C written binary file with IDL [message #79235 is a reply to message #79234]

Thu, 09 February 2012 20:56

manodeep@gmail.com
Messages: 33
Registered: June 2006

Member

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).

In general, the padding is compiler specific -- so there is no
standard way of reading in those binary files into IDL/other codes.
The best bet would be to write out the individual fields of the
structure and then read them back into IDL.

HTH,
Manodeep

On Feb 9, 9:44 pm, bing999 <thibaultga...@gmail.com> wrote:
> Hi,
>
> I am having a problem with reading a C written binary file with IDL.
> It may come from differences of type definitions between C and IDL but
> I could not really figure out from Google...
>
> In C, it writes a structure containing the following variable types:
>
> struct MyStruct
> {
> int a;
> long long b;
> int c;
> float d;
>
> };
>
> Then, in IDL, I read this with:
>
> MyStruct = {$
> a : 0L, $
> b : 0LL, $
> c : 0L, $
> d : 0.0 $
> }
>
> openr, 1, filename, /SWAP_IF_BIG_ENDIAN
> readu, 1, MyStruct
> close, 1
>
> but this gives me wrong values.
>
> Did I miss something about the type conversion??
>
> If someone could please clarify this, it would really help!
> Thanks !

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[Message index]

		Re: read a C written binary file with IDL By: Paul Van Delst[1] on Fri, 10 February 2012 08:02
		Re: read a C written binary file with IDL By: Bill Nel on Fri, 10 February 2012 07:12
		Re: read a C written binary file with IDL By: Paul Van Delst[1] on Fri, 10 February 2012 06:09
		Re: read a C written binary file with IDL By: Thibault Garel on Thu, 09 February 2012 21:08
		Re: read a C written binary file with IDL By: manodeep@gmail.com on Thu, 09 February 2012 20:56
		Re: read a C written binary file with IDL By: Thibault Garel on Mon, 20 February 2012 17:49

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