OpenEuphoria

Re: Errors in function trim() (ESL0.01)

• Posted by Kenneth Rhodes <ken_rhodes30436 at yahoo.com> Mar 29, 2006
• 480 views

Juergen Luethje wrote:
> 
> Pete Lomax wrote:
> 
> > On Sun, 26 Mar 2006 23:08:57 -0800, "Julio C. Galaret Viera"
> > <guest at RapidEuphoria.com> wrote:
> > 
> >> I found errors both in syntax and algorithm in the trim() function
> >> (string.e).
> > <snip>
> > This should be faster (possibly by as much as a factor of 5, though in
> > most cases less) and does not crash when passed eg "" or "   ":
> > }}}
<eucode>
> > global function trim(sequence str)
> > --
> > -- remove leading and trailing whitespace.
> > --
> > integer slicestart, sliceend
> >     slicestart=1
> >     sliceend=length(str)
> >     while slicestart<=sliceend
> >       and find(str[slicestart]," \t") do
> >         slicestart += 1
> >     end while
> >     while sliceend>slicestart
> >       and find(str[sliceend]," \t") do
> >         sliceend -= 1
> >     end while
> >     -- avoid performing a slice unless we have to, since it
> >     --  requires a mem alloc/copy; [improves performance]
> >     if slicestart>1 or sliceend<length(str) then
> >         return str[slicestart..sliceend]
> >     end if
> >     return str
> > end function
> > </eucode>
{{{

> 
> I would replace " \t" with a variable, say 'charsToTrim', and then call
> the function like this:
> 
> }}}
<eucode>
> global function trim_chars(sequence str, sequence charsToTrim)
>    ...
> end function
> </eucode>
{{{

> 
> So someone can use this function for removing leading and trailing dots
> or whatever. The normal trim() function then could be implemented like
> this:
> 
> }}}
<eucode>
> constant WSP = " \t\r\n"
> 
> global function trim(sequence str)
>    return trim_chars(str, WSP)
> end function
> </eucode>
{{{

> 
> Regards,
>    Juergen
> 
> -- 
> Have you read a good program lately?

For what its worth, Ricardo Forno's genfunc.e
http://www.rapideuphoria.com/genfunc.zip
has the following routines:

--Initializes vector for Trim functions.
--'p' is a string containing the characters defined to be whitespace.
function TrimInit(sequence p)
    sequence s
    s = repeat(1, 256)
    for i = 1 to length(p) do
	s[p[i] + 1] = 0
    end for
    return s
end function

constant NOTBLANK = TrimInit(" \t\n")

--/topic STRING / SEQUENCE
--/func TrimHead(sequence s)
--/desc Trims whitespace in front of a string
--/ret The argument without whitespace at the beginning
--Change "sequence s" to "String s" to force type checking.
--Example: TrimHead("    E u  ") gives "E u  "
global function TrimHead(sequence s)
    integer len
    len = length(s)
    for i = 1 to len do
	if NOTBLANK[s[i] + 1] then
	    return s[i..len]
	end if
    end for
    return {}
end function

--/topic STRING / SEQUENCE
--/func TrimTail(sequence s)
--/desc Trims whitespace at end of a string
--/ret The argument without whitespace at the end
--Change "sequence s" to "String s" to force type checking.
--Example: TrimTail("   E u   ") gives "   E u"
global function TrimTail(sequence s)
    for i = length(s) to 1 by - 1 do
	if NOTBLANK[s[i] + 1] then
	    return s[1..i]
	end if
    end for
    return {}
end function

--/topic STRING / SEQUENCE
--/func TrimBoth(sequence s)
--/desc Trims whitespace at both ends of a string
--/ret The argument without whitespace at both ends
--Change "sequence s" to "String s" to force type checking.
--Example: TrimBoth("  E u   ") gives "E u"
global function TrimBoth(sequence s)
    return TrimTail(TrimHead(s))
end function

I've always thought of Ricardo's genfunc.e as
an ESL already done.

Ken Rhodes
Folding at Home: http://folding.stanford.edu/
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