| Re: (NOT SO) Dumb problem with STRPOS [message #4732] |
Sun, 16 July 1995 00:00 |
lkramer
Messages: 5
Registered: July 1995
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Junior Member |
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> From: steele@aragorn.phys.ucalgary.ca (Dave Steele)
> Newsgroups: comp.lang.idl-pvwave
> Subject: Dumb problem with STRPOS
> Date: 14 Jul 1995 19:22:47 GMT
> Organization: Institute for Space Research
> Can someone explain the following behaviour to me?
> IDL> help,/st,!version ; Here's the situation.
> ** Structure !VERSION, 3 tags, length=24:
> ARCH STRING 'mipseb'
> OS STRING 'RISC/os'
> RELEASE STRING '3.1.0'
> IDL> test='c000.' ; define a string
> IDL> help,test ; check it is a string
> TEST STRING = 'c000.'
> IDL> print,strpos(test,'000') ; search for a substring
> 1
> IDL> print,strpos(test,'000.') ; and a slightly different one
> 1
> IDL> test='c0000.' ; add a '0'
> IDL> help,test
> TEST STRING = 'c0000.'
> IDL> print,strpos(test,'000') ; search again
> 1
> IDL> print,strpos(test,'000.') ; Why isn't this substring found???
> -1
> I checked the manual for this version and it says nothing that would
> explain this. BTW, it's nothing to do with octal constants.
> All suggestions gratefully received!
Dave:
This is a definite Bug. I am using Window 3.6.1. Get identical response.
You have probably already found out that:
IDL> print,test
c0000.
IDL> print,strpos(test,'0000.') ; a longer search string.
1
IDL> print,strpos(test,'000.') ; your search string.
-1
IDL> print,strpos(test,'00.') ; a shorter search string.
3
and also
IDL> print,test
c0000X
IDL> print,strpos(test,'000X') ; different terminal character.
-1
This is a very scary bug. I can't find the source for strpos.pro in the
library so it must be part of the dynamic run executable.
I re-wrote strpos calling it strpos1. It performs as follows:
IDL> print,test
c0000.
IDL> print,strpos1(test,'0000.')
1
IDL> print,strpos1(test,'000.')
2
IDL> print,strpos1(test,'00.')
3
IDL> print,strpos1(test,'0.')
4
and here is the text of the routine.
---------------------------cut here-------------------------
function strpos1,targ,srch,pos
targ=string(targ)
srch=string(srch)
if (n_elements(pos) eq 0) then pos = 0
t=byte(targ)
n=n_elements(t)
m=strlen(srch)
p=lindgen(m)
i=pos
for i=pos,n do begin
if (srch eq string(t(p+i)))then return,i
endfor
return ,-1
end
--------------------------end of routine ------------------
I do not have time to properly document this. RSI really should fix
it.
E-mail me if you have questions. I tried to reply directly but the mail was
returned (?).
------------------------------------------------------------ ---------
Leonard Kramer, Ph.D. Physicist.
AGAR Corporation, (Process Measurement & Control)
POB 802127 Houston, TX 77280-2127
email: lkramer@neosoft.com
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