Re: quoted null character

[Martin Schultz <martin.schultz(at)dkrz.de>]

George McCabe wrote:
> 
> hello,
> 
> i had one hell of a time today figuring out some unexpected results in
> IDL string processing, and i wonder of any one has encountered similar
> problems.
> 
> take the following code segment -
> 
> IDL> ; the variable 'F' is string type result from another procedure
> IDL> cmd = 'perl -e '+"'"+'$_ = '+'"'+F+'"'+' ; print if (
> m/AC[0-9]{13}.L0/ )'+"'"
> IDL> print, cmd
> IDL> spawn,cmd,res
> IDL> print, res
> 
> what is executed by the unix shell is -
> perl -e '$_ = "<string>" ; print if ( m/AC[0-9]{13}.L0/ )'
> 
> except, when...
> 
> in case when the string in variable 'F' ends in a null character.
> then one gets an incomplete concatenation beyond the null.  since i'ld
> already spent an hour or so rearranging quote marks and parting up the
> process to find the problem, i didn't spend time after discovering the
> cause to figure out if IDL was interpreting the null as a quote or
> other weird possibilities.
> 
> anyone?
> 
> Thank you, George
> 

hmmm. All I can say is that print,byte('') yields 0. This may be the
problem and the 
solution ?

To get rid of all null characters in a string (i.e. replace them with
blanks e.g.),
do the following:
   bf = byte(F)   ; byte representation of string F
   rc = (byte(' '))[0]  ; byte repr. of replacement character (blank)
   w = where(bf eq 0,count)
   if count gt 0 then bf[w] = rc
   newF = string(bf)
...

This functionality is implemented in my (heavily revised) strrepl
function which I
attach below (and which has become obsolete by IDL 5.3 ?).

Cheers,
Martin



-- 
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
[[ Dr. Martin Schultz   Max-Planck-Institut fuer Meteorologie    [[
[[                      Bundesstr. 55, 20146 Hamburg             [[
[[                      phone: +49 40 41173-308                  [[
[[                      fax:   +49 40 41173-298                  [[
[[ martin.schultz@dkrz.de                                        [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
; $Id: strrepl.pro,v 1.10 1999/01/22 20:12:17 mgs Stab $
;-------------------------------------------------------------
;+
; NAME:
;        STRREPL (function)
;
; PURPOSE:
;        Replace all occurences of one character in a string
;        with another character. The character to be replaced
;        can either be given as string of length 1 or as an
;        index array containing the character positions
;        (see strwhere). This function also works for string arrays.
;
; CATEGORY:
;        String Routines
;
; CALLING SEQUENCE:
;        Result = STRREPL(str, fromchar, tochar [,/IGNORECASE])
;
; INPUTS:
;        STR      -> the string to be changed
;
;        FROMCHAR -> either: a string of length 1 (the character to 
;                        be replaced)
;                    or: an index array with the character positions
;
;        TOCHAR   -> replacement character
;
; KEYWORD PARAMETERS:
;        IGNORECASE -> if set, fromchar will be treated case-insensitive
;              (only if fromchar is a character)
;
; OUTPUTS:
;        A string of same length as the input string
;
; SUBROUTINES:
;
; REQUIREMENTS:
;
; NOTES:
;        Uses SIZE(/TYPE) available since IDL 5.2
;
; EXAMPLES:
;        ; Convert a Unix filename to Windows
;        ufile = '/usr/local/idl/lib/test.pro'
;        wfile = 'c:' + strrepl(ufile,'/','\')
;        print,wfile
;        ; prints "c:\usr\local\idl\lib\test.pro"
;
;        ; Use with index (uses strwhere function)
;        a = 'abcdabcdabcd'
;        index = [ strwhere(a,'a'), strwhere(a,'b') ] > 0
;        print,strrepl(a,index,'#')
;        ; prints  "##cd##cd##cd"
;
; MODIFICATION HISTORY:
;        mgs, 02 Jun 1998: VERSION 1.00
;        mgs, 24 Feb 2000: - rewritten
;                          - now accepts character argument
;                          - added IGNORECASE keyword
;
;-
; Copyright (C) 1998-2000, Martin Schultz
; This software is provided as is without any warranty
; whatsoever. It may be freely used, copied or distributed
; for non-commercial purposes. This copyright notice must be
; kept with any copy of this software. If this software shall
; be used commercially or sold as part of a larger package,
; please contact the author to arrange payment.
; Bugs and comments should be directed to mgs@io.harvard.edu
; with subject "IDL routine strrepl"
;-------------------------------------------------------------


function strrepl,str,fromchar,tochar,IGNORECASE=ignorecase
 
ON_ERROR,2    ; return to caller

     ; argument testing
     if n_params() lt 3 then begin
        message,'Usage: strrepl,str,fromchar,tochar[,/IGNORECASE])'
     endif

     ; make working copy of string and convert to a byte array
     bstr = byte(string(str))
      
     ; fromchar is given as character
     if size(fromchar,/TYPE) eq 7 then begin
        ; ignore case?
        if keyword_set(ignorecase) then begin
           ; call strrepl recursively w/o the IGNORE_CASE keyword
           res1 = strrepl(str,strupcase(fromchar),tochar)
           res2 = strrepl(res1,strlowcase(fromchar),tochar)
           return,res2
        endif else begin
           ; find all character occurences
           ; must be a single character - use the first
           bfc = (byte(fromchar))[0]
           ; go and search
           w = where(bstr eq bfc,count)
           ; if not found, return original string
           if count eq 0 then return,str
        endelse
     endif else begin
     ; fromchar is already an index array
        w = long(fromchar)
     endelse

     ; make sure index is in range
     test = where(w lt 0 OR w ge n_elements(bstr),tcount)
     if tcount gt 0 then begin
        message,'WARNING: Index out of range!',/Continue
        ; restrict to valid index values
        test = where(w ge 0 AND w lt n_elements(bstr),tcount)
        if tcount gt 0 then begin
           w = w[test]
        endif else begin
        ; no valid indices: return original string
           return,str
        endelse
     endif

     ; convert tochar to a byte value
     btc  = (byte(tochar))[0]
 
     ; replace 
     bstr[w] = btc
 
     ; return result as string
     return,string(bstr)
 
end