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strange GT and LT behavior [message #89468]

Mon, 20 October 2014 08:41

markb77
Messages: 217
Registered: July 2006

Senior Member

I've encountered a bizarre situation where IDL thinks that 0 is less than a negative number. Can anyone rationalize this? Is it really not ok to compare the value of an unsigned integer with a signed integer? Shouldn't the compiler handle this?

test case:

pro test_gt_lt

a = ulong64(0)

b = long(100)

if (a lt b) then begin

print, 'ZERO IS LESS THAN 100'

endif else begin

print, 'ZERO IS GREATER THAN 100'

endelse

c = ulong64(0)

d = long(-100)

if (c lt d) then begin

print, 'ZERO IS LESS THAN -100'

endif else begin

print, 'ZERO IS GREATER THAN -100'

endelse

end

OUTPUT:
ZERO IS LESS THAN 100
ZERO IS LESS THAN -100

IDL> print, !version
{ x86_64 Win32 Windows Microsoft Windows 8.3 Nov 15 2013 64 64}

thanks
Mark

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[Message index]

		strange GT and LT behavior By: markb77 on Mon, 20 October 2014 08:41
		Re: strange GT and LT behavior By: Dick Jackson on Mon, 20 October 2014 09:35
		Re: strange GT and LT behavior By: markb77 on Mon, 20 October 2014 09:48
		Re: strange GT and LT behavior By: Craig Markwardt on Mon, 20 October 2014 14:28
		Re: strange GT and LT behavior By: markb77 on Tue, 21 October 2014 04:01

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