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Re: File sizes and the SAVE command [message #48053 is a reply to message #48052]

Wed, 22 March 2006 03:08

Paolo Grigis
Messages: 171
Registered: December 2003

Senior Member

Carsten Pathe wrote:
> Hi there,
>
> I am wondering about the IDL save command and the disk space of the
> created save files.
> Just an simple example:
>
> a=intarr(100000)
> tmp = size(a)
> print, string(format='(f10.3)',(tmp(1)*tmp(2))/(2.^10.))+' kbyte'
> ;195.313 kbyte
> save, a, filename='d:\temp\test\b.dat'
>
> b=fltarr(100000)
> tmp = size(b)
> print, string(format='(f10.3)',(tmp(1)*tmp(2))/(2.^10.))+' kbyte'
> ;390.625 kbyte
> save, a, filename='d:\temp\test\a.dat'
>
> c=dblarr(100000)
> tmp = size(c)
> print, string(format='(f10.3)',(tmp(1)*tmp(2))/(2.^10.))+' kbyte'
> ;488.281 kbyte
> save, c, filename='d:\temp\test\c.dat'
>
> When you look at the created files and their sizes, you will see the
> following:
> a.dat 393 kb
> b.dat 393 kb
> c.dat 784 kb
>
> If you compare the file sizes to the sizes, the arrays were allocating
> in the memory before they were save to disk, you see differences which
> will cost you a lot of disk space when saving arrays of several hundred
> megabytes.
> Does anybody know, why the save command is producing files larger than
> they should be?

Because (size(a))[2] is the type code, which has nothing to do with the byte
size of each type, which is:

TYPE #BYTES

Byte 1
Integer 2
Unsigned Integer 2
Long 4
Unsigned Long 4
64-bit Long 8
64-bit Unsigned Long 8
Floating-point 4
Double-precision 8

Ciao,
Paolo

>
> PS: I know, that I can also use:
> openw, 10, 'd:\temp\test\a.dat'
> writeu, 10, a
> close, 10
> But when I want to restore the data, I have to know the structure of the
> data to restore - which is not always the case.
>
> Thanks a lot help

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[Message index]

		Re: File sizes and the SAVE command By: Maarten[1] on Wed, 22 March 2006 07:27
		Re: File sizes and the SAVE command By: Klaus Scipal on Wed, 22 March 2006 07:17
		Re: File sizes and the SAVE command By: R.Bauer on Wed, 22 March 2006 05:26
		Re: File sizes and the SAVE command By: Klaus Scipal on Wed, 22 March 2006 03:58
		Re: File sizes and the SAVE command By: Maarten[1] on Wed, 22 March 2006 03:10
		Re: File sizes and the SAVE command By: Paolo Grigis on Wed, 22 March 2006 03:08

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