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C Alignment/IDL structures [message #43098]

Wed, 16 March 2005 08:13

joey
Messages: 5
Registered: March 2005

Junior Member

Hi! I have an C library which I link into IDL using IDL_MakeStruct. The
structure I link in with IDL is not a true C structure, but a dynamic
structure I create on the fly depending on the data I wish to have within
IDL.

It works quite well; however, one of the elements incorporated in my
structure is another structure which I would like to add a double value.

When I add this double, my structure size seems to get the wrong size for
IDL to handle so nothing will work when accessing the structure. I compute
the size to a value which is the sum of all bytes in the structure which
obviously does not take into account the packing/aligning that C does.

My question is: is there a way I can figure out how many bytes to malloc
such that IDL and I will always be in agreement?

Even if we are in agreement, I need to know where the padding will occur so
I would like to have the same algorithm that IDL uses to compute its
structure allocation when given a list of tags.

If I stick to floats/long/int/etc/strings/etc. everything seems to work
great. Its only when adding the double that everything goes bad.

Thanks for any advice!

Joey

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[Message index]

		C Alignment/IDL structures By: joey on Wed, 16 March 2005 08:13
		Re: C Alignment/IDL structures By: joey on Mon, 21 March 2005 08:56
		Re: C Alignment/IDL structures By: Randall Skelton on Wed, 16 March 2005 10:07

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