| Re: subtle but important [message #24908] |
Fri, 27 April 2001 09:12 |
Paul van Delst
Messages: 364
Registered: March 1997
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Senior Member |
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Craig Markwardt wrote:
>
> Randall Skelton <rhskelto@atm.ox.ac.uk> writes:
>> On Fri, 27 Apr 2001, Liam E. Gumley wrote:
>>
>>> This is a subtle but important point. DOUBLE() is a type conversion
>>> function [snip]
>>
>> While we are on the subject of 'subtle but important points' in IDL...
>>
>> I also learned today that for integers the default length is 16-bit unless
>> you use the "COMPILE_OPT DEFINT32" statement. Try "print, 1000*1000" in
>> IDL.
>
> Appending "L" to integers saves a lot of grief later on.
This is an understatement
Maybe it's my fortran background, but I always stick an "L" on the end of integers so I
know (and others who read the code after me) that this value is a LONG (read: 4 byte)
integer, even for silly stuff like
n = 3L
FOR i = 0L, n - 1L DO BEGIN
.....
ENDFOR
In this case there's no need but one day someone might make "n" greater than what a 2-byte
int can hold.
Don't they teach this sort of stuff (and the floating point representation stuff) in
computing/science courses anymore?
paulv
--
Paul van Delst A little learning is a dangerous thing;
CIMSS @ NOAA/NCEP Drink deep, or taste not the Pierian spring;
Ph: (301)763-8000 x7274 There shallow draughts intoxicate the brain,
Fax:(301)763-8545 And drinking largely sobers us again.
paul.vandelst@noaa.gov Alexander Pope.
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| Re: subtle but important [message #24911 is a reply to message #24908] |
Fri, 27 April 2001 08:28  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Randall Skelton <rhskelto@atm.ox.ac.uk> writes:
> On Fri, 27 Apr 2001, Liam E. Gumley wrote:
>
>> This is a subtle but important point. DOUBLE() is a type conversion
>> function [snip]
>
> While we are on the subject of 'subtle but important points' in IDL...
>
> I also learned today that for integers the default length is 16-bit unless
> you use the "COMPILE_OPT DEFINT32" statement. Try "print, 1000*1000" in
> IDL.
That's why I often use "print, 1000L*1000L". Appending "L" to
integers saves a lot of grief later on. The COMPILE_OPT approach
works in newer versions, but not in IDL 5.2 or older.
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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