Re: R: invoking the correct memory management from C files

[Jaroslav Hajek]

On Wed, May 5, 2010 at 4:02 PM, Peter L. Soendergaard
<address@hidden> wrote:
> ons, 05 05 2010 kl. 13:42 +0000, skrev Riccardo Corradini:
>> Could you please show an example?
>>
>>
>>
>
> I my C-library the code typically looks something like this:
>
> void dgtreal_long(....)
> {
>   LTFAT_COMPLEX *gf = ltfat_malloc(L*sizeof(LTFAT_COMPLEX));
>
>   .. do stuff ...
>
>   ltfat_free(gf);
> }
>
> If I build it as a standalone library, ltfat_malloc and Ltfat_free are
> given by:
>
> void* ltfat_malloc (size_t n)
> {
>  return fftw_malloc(n);
> }
>
> void ltfat_free(void *ptr)
> {
>  fftw_free(ptr);
> }
>
> For Octave I would like to define ltfat_malloc as something like (not
> tested!):
>
> void* ltfat_malloc (size_t n)
> {
>  OCTAVE_LOCAL_BUFFER (unsigned char, tmp, n);
>  return tmp;
> }
>
> Should I just declare ltfat_free to be empty, or is there a better
> solution?
>

No, this is completely wrong. OCTAVE_LOCAL_BUFFER, as the name
suggests, declares a buffer *local* to the enclosing scope, which is
automatically deallocated when the scope ends. Hence, in your
function, tmp is deallocated immediately after return, so it returns
an invalid pointer. Local buffers have a FIFO ordering and they take
advantage of this to employ an efficient allocation scheme.

-- 
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz