[Rd] "warning: assignment discards qualifiers from pointer target type"

[Duncan Murdoch]

On 11-06-09 7:27 AM, oliver wrote:
> On Wed, Jun 08, 2011 at 08:35:34PM -0400, Simon Urbanek wrote:
>>
>> On Jun 8, 2011, at 8:32 PM, oliver wrote:
>>
>>> On Thu, Jun 09, 2011 at 02:17:31AM +0200, oliver wrote:
>>> [...]
>>>> OK, I looked at this now.
>>>>
>>>> LENGTH() checks the length of the vector.
>>>>
>>>> Good to know this.
>>>>
>>>> So the problem of a vector of length 0 can be with any arguments of type SEXP,
>>>> hence I will need to check ANY arg on it's length.
>>>>
>>>> This is vital to stability under any situation.
>>>>
>>>> Thanks for this valuable hint!
>>>>
>>>> I will add checks for all my SEXP-args.
>>> [...]
>>>
>>> Hey, LENGTH() does not work with String-vectors! :(
>>>
>>
>> Of course it does ...
>>
>>
>
> It does not so on my R 2.10.1 installation.
>
>
> In the R-Shell I get:
>
>    ==============================
>    >  length(c())
>    [1] 0
>    >
>    ==============================
>
> So c() is vec of length 0.
>
> When I feed my readjpeg() with c() as filename arg,
>
> testing with:
> ====================================================
>    if( LENGTH( filename_sexp )<  1 )
>    {
>      error("LENGTH( filename_sexp )<  1");
>      //error("filename can't be vector of length 0");
>    }
>    else
>    {
>      error("LENGTH( filename_sexp ) is not<  1");
>    }
> ====================================================
>
>
> I got:
>    Error in readjpeg(filename = c()) : LENGTH( filename_sexp ) is not<  1
>
>
> You can explain why?

c() doesn't create a STRSXP, it is NULL, which is a NILSXP.  LENGTH() 
doesn't work on that object.  (I'd recommend using length() rather than 
LENGTH(); it's a function, not a macro, and it does give the expected 
answer.)

Duncan Murdoch