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N_TAGS( , /LENGTH) strange result! [message #13900]

Wed, 06 January 1999 00:00

Luis Oliveira
Messages: 4
Registered: November 1998

Junior Member

Hi all readers.

My problem with N_TAGS(?,/LENGTH) is that it's result with some structures
is diferent from the size of the files that That structures originate?!
(Diferences of about 3 or 4 bytes.)

I am using IDL to read some unformated data file that was written with a C
program. The size calculated with the C structures was the same as the size
of that structures in files. N_TAGS gives a diferent value, but when I
write the same structure with IDL to a file, it's size is the same as the C
structures!

My IDL version is 5.11 in a windows95 PC.

Thanks for any light on this subject...

Luis

PS: After some tests, I've seen that this happens with structures that have
members that are structures... here goes an example:

IDL> x={a:0L,b:0,c:bytarr(5),d:0B,e:bytarr(3),g:{a:0B,b:0}}
IDL> print,n_tags(x,/length)
20
IDL> x={a:0L,b:0,c:bytarr(5),d:0B,e:bytarr(3),g:{a:0B,b:0},f:0B}
IDL> print,n_tags(x,/length)
24

This two structures only differ by one byte! The real length is 18 and 19.
Now, if I write the structure to a file:

IDL> openw,1,'lixo.txt',/delete
IDL> writeu,1,x
IDL> print,(fstat(1)).size ;To return the size of the file
19
IDL> close,1

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[Message index]

		N_TAGS( , /LENGTH) strange result! By: Luis Oliveira on Wed, 06 January 1999 00:00
		Re: N_TAGS( , /LENGTH) strange result! By: mgs on Tue, 05 January 1999 00:00

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