From: "Brett H. Williams" <brett_williams@...>
Date: 2003-07-25T05:54:39+09:00
Subject: Re: SWIG and char * parameters

On Jul 25, Ben Giddings wrote:
> I've just started to try to use SWIG to wrap a bunch of C functions so I can 
> call them from Ruby.  If I can get this working it will make some testing 
> much easier, but I've come across a strange problem.  Functions which take 
> char pointer arguments seem to pass in NULL.
> 
> #####
> 
> void sayHelloTo(char *name) {
>   if (NULL == name) {
>     printf("Hello %s\n", name);
>   }
>   else {
>     printf("Gimme a name!\n");
>   }
> }
> 
> #####
> 
> ben% irb
> irb(main):001:0> require 'sample'
> => true
> irb(main):002:0> Sample.sayHello
> Hello World
> => nil
> irb(main):003:0> Sample.sayHelloTo
> ArgumentError: wrong # of arguments(0 for 1)
>         from (irb):3:in `sayHelloTo'
>         from (irb):3
> irb(main):004:0> Sample.sayHelloTo("Bob")
> Gimme a name!
> => nil
> 
> I've looked over the documentation on the generic and Ruby-specific parts of 
> the SWIG site and haven't found anything talking about this issue.  Any tips, 
> pointers, URLs or comments?

Looks like it does exactly what you told it to.  You passed in Bob.
Therefore, NULL != name, and so it says "Gimme a name!".

Try passing in nil, you'll get a seg fault :)

What you want is NULL != name.

Not SWIG, just C.

HTH,

-- 
---------------------------------------------- | --------------------------
Brett Williams                                 | 
---------------------------------------------- | --------------------------