Re: [Swig-user] When %varargs used with a numeric argument, NULL terminator not automatically added in python from 2.0.6 on, requires None arg

[William S F. <ws...@fu...>]

On 15/04/13 15:32, Kyle Nolan wrote:
>
> I have a C++ function:
>      string dm_cli::show (char *mode, ...)
> And the swig.i file says:
>      %varargs(6,char *arg = NULL) show;
>
> I was using swig 1.3.21 with python 2.6.6 and didn't have any issues
> calling show("programs")
>
> However, another user was trying from their swig 1.3.39 and it was
> failing saying the args were incorrect.
> It no longer seemed to know where the end of the varargs were. I had to
> manually specify the None:
>      show("programs", None)
>
> I am parsing out the args using va_start just as is shown in the swig
> documentation:
>      va_start(voptargs,mode);
>      s = va_arg(voptargs, char *);
>      while (s) {
>         ...
>         s = va_arg(voptargs, char *);
>      }
>      va_end(voptargs);
>
> I searched the release notes and bugs and found this comment on the
> 2.0.4 changes:
>
> 2011-05-14: wsfulton
>   %varargs when used with a numeric argument used to create an
> additional argument
>   which was intended to provide a guaranteed sentinel value. This never
> worked and now
>   the additional argument is not generated.
>
> So I tried 2.0.4 and that failed but 2.05 worked. However 2,0,6 through
> 2.0.9 all failed.
>
> the pywrap.cxx file generated by 2.0.5 and 2.0.6 looks identical.
>
This is then indicative of some undefined behaviour problem possibly 
elsewhere else in your own code.

> This issue seems to be specific to python--I did not have any issues
> with the TCL generated interface.
>
> Is there some trick to getting %varargs with a numeric argument working
> with python so that swig automatically inserts the NULL terminator?
> Is this a known bug? I couldn't find it in the list of open/closed bugs.
>
Have you read the most up to date documentation, currently at 
http://www.swig.org/Doc2.0/Varargs.html#Varargs_nn5. In particular are 
you using the "compactdefaultargs" feature?

Please provide a small cutdown test case of your issue if the above 
information doesn't help.

William