Changing data type in octave_value_list

[Joshua Rigler]

This might be more of a C/C++ question, so please be kind...

I am writing a .oct file, and the source includes the following standard 
definition at the beginning:

  DEFUN_DLD (cdflib, args, nargout, "...whatever...")

As I understand things, 'args' is my input list, passed from the 
interpreter, and of type octave_value_list.  I want to be able to pass 
one of my inputs as either a scalar, or a string that I can then 
convert/map to a corresponding scalar and place back into the same 
position in args, before proceeding to subsequent operations.

What I naively thought I could do is (paraphrased):

  if (args(0).is_string)
  {
    args(0) = double (convert_s2i(args(0).string_value) );
  }

...where 'convert_s2i' is just a function that maps certain strings to 
long integers, which I am then happy to store as double-floats, since 
this is what Octave expects (I suppose newer versions have support for 
additional data types, including integers, but I'm perfectly happy with 
doubles).  Note, I am not simply trying to convert an ascii '1' into its 
scalar equivalent, but rather a multi-character string that associates 
with a particular integer inside a C++ map object.

Anyway, the problem I face is that I keep getting the following error:

  error: invalid conversion from string to real scalar

I assume this corresponds to my attempt to transform args(0) from a 
string into a scalar.  Is there a straight-forward way to do this?
Thanks.

-EJR