| [Q] readf into an array error [message #5725] |
Fri, 02 February 1996 00:00 |
Iarla Kilbane-Dawe
Messages: 7
Registered: May 1995
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Junior Member |
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Hello,
why does IDL give me an error when I try to do?
a=fltarr(10)
i = 0
readf,unit,a(i)
Many thanks,
Iarla.
____________________________________________________________ _________
Iarla Kilbane-Dawe Email: iarla@atm.ch.cam.ac.uk
Centre for Atmospheric Science Phone: ++44 (01223) 336524
Cambridge University Fax: ++44 (01223) 336473
____________________________________________________________ _________
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| Re: [Q] readf into an array error [message #5729 is a reply to message #5725] |
Fri, 02 February 1996 00:00  |
Ken Knighton
Messages: 44
Registered: May 1995
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Member |
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> why does IDL give me an error when I try to do?
>
> a=fltarr(10)
> i = 0
> readf,unit,a(i)
>
I'm not sure why IDL gives you an error, but
readf, unit,a(i)
is not going to read anything. a(i) is an expression rather than a
variable. The readf statement requires a named variable in order to
read anything. Try using
a=fltarr(10)
i=0
b=0.0
readf, unit, b
a(i)=b
This is actually mentioned somewhere in the i/o chapter of the user's
manual.
Also, you might want to look at the ASSOC() function and associated i/o.
Because you are reading an array, this might be a better solution.
Ken Knighton knighton@gav.gat.com knighton@cts.com
General Atomics
San Diego, CA
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| Re: [Q] readf into an array error [message #5732 is a reply to message #5725] |
Fri, 02 February 1996 00:00 |
peter
Messages: 80
Registered: February 1994
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Member |
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Iarla Kilbane-Dawe (iarla@atm.ch.cam.ac.uk) wrote:
: Hello,
: why does IDL give me an error when I try to do?
: a=fltarr(10)
: i = 0
: readf,unit,a(i)
This is due to the argument passing mechanism used in IDL. If an array
is passed to a function, it is passed by reference. If a subarray is
passed, it is passed by value, and thus cannot be overwritten.
To accomplish what you want, you need to do
temp = a(i)
readf,unit,temp
a(i) = temp
It is ugly! The syntax gives no clue what is happening, and the
manual is exceptionally obscure.
Peter
--------------------------------
Peter Webb, HP Labs Medical Dept
E-Mail: peter_webb@hpl.hp.com
Phone: (415) 813-3756
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| Re: [Q] readf into an array error [message #5734 is a reply to message #5725] |
Fri, 02 February 1996 00:00 |
M.W.Gardner
Messages: 7
Registered: November 1995
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Junior Member |
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Iarla Kilbane-Dawe <iarla@atm.ch.cam.ac.uk> wrote:
> why does IDL give me an error when I try to do?
>
> a=fltarr(10)
> i = 0
> readf,unit,a(i)
>
Iarla, what error do you get and what exactly are you attempting to do ?
if you haven't defined the unit you get "% READF: Variable is undefined: UNIT"
if unit is defined (eg given a number say 1) and has not been defined in an
open statement you get "% READF: File unit is not open: 1"
If you are trying to read from a file a ten element array then open you file,
read in the data, and close the file like so :
a=fltarr(10)
open,unit,'filename',/get_lun
read,unit,a
close,unit
free_lun,unit
and that should do it. If you don't want to do this then ignore all that and
let me know what you want to do !
Anyway, I hope that helps, if not provide some more info if I have missed the
point.
Matt
--
-----> Matt Gardner EMAIL->m.W.gardner@uea.ac.uk PHONE->+44- 1603-592041
School of Environmental Science,University of East Anglia,Norwich,NR4 7TJ,UK
------------------------------------------------------------ ------------------
opinions are mine - http://www.uea.ac.uk/~e449
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