Patches to clean up string-handling corner cases

[Ethan M. <merritt@u.washington.edu>]

On Saturday 04 June 2005 10:06 am, J=C3=BCrgen Wieferink wrote:
> Today I've searched the code for other occurances of
> 'free(...string_val)' and replaced them by 'gpfree_string'.

Great. I put that one in cvs.

> The third patch keeps track of backslashes within double quoted strings.

I had forgotten about this issue.  I've put your fix into cvs
because it is better than the current state of affairs.=20
But I don't think this is the end of the story.  I see it as=20
applying a bandaid to the deeper problem of extending the=20
distinction between single-quoted strings and double-quoted
string constants to string variables.

Currently the check for single- or double- quotes is made at
the time a string constant is parsed, as in:
  A =3D "1\n2"
  B =3D '1\n2'
  if (A ne B) print "Strings are not equal"

But if you assign a value to a string variable via some more
complex path, including your new system() function, then there
is no check for whether embedded special characters should be
given the single-quote treatment (store raw input) or the
double-quote treatment (add \ in front of certain characters).

I don't have a specific example of when this would cause a
problem, but it makes me uneasy.  I think it might be better to
remove the single/double quote processing from the parser, and
instead *always* store a string in its "raw" form, and add a
separate flag to indicate whether it is to be expanded or not
when printed.

>The second problem I found is revealed by:
>  set macros
>  foo =3D "print foo"
>  @foo
>  print "@foo"
>  print "\"@foo\""
>  print "\"@foo"; @foo

I haven't looked at this one yet, but there's another unresolved
issue as well, pointed out by Petr Mikulik a while back.
As you can see from the sequence below, it does not
work to define and invoke a macro on the same input line:

gnuplot> set macros
gnuplot> foo =3D "1"; print @foo;  foo =3D "2"; print @foo
         warning: foo is not a string variable
         warning: foo is not a string variable

gnuplot> foo =3D "1"; print ;  foo =3D "2"; print=20
                          ^
         constant expression required

gnuplot> show var

        Variables:
        pi =3D 3.14159265358979
        foo =3D 1

gnuplot> foo =3D "2"; print @foo;  foo =3D "3"; print @foo
1
1


=2D-=20
Ethan A Merritt       merritt@u.washington.edu
Biomolecular Structure Center
Mailstop 357742
University of Washington, Seattle, WA 98195