trouble with C pointers and GC

trouble with C pointers and GC

[Patrick Goldbronn - SYSCO]

Hello,

I have some trouble to return a structure with pointers outside the heap
!

I allocate two C pointer :

  adr1 = (double *) calloc(nb1,sizeof(double)); 
  adr2 = (int *) calloc(nb2,sizeof(int)); 

and I want to put it in a value with Final_tag :

  result = alloc_final( n , free_function , nb_elm*2 , 1  ) ;

I don't know what is the value of n (n words) : A pointer value
represent 1 word or 2 ?

How can I store the pointers adr1 and adr2 in value result and how can I
retrieve them (with Store_field and Field ?) ?

Thank you for your assistance.

-- 
######################
# Patrick GOLDBRONN  #
# CEA- DRN/DMT/SYSCO #
######################

Re: trouble with C pointers and GC

[doligez]

>From: Patrick Goldbronn - SYSCO <patrick.goldbronn@cea.fr>

>  adr1 = (double *) calloc(nb1,sizeof(double)); 
>  adr2 = (int *) calloc(nb2,sizeof(int)); 
>
>and I want to put it in a value with Final_tag :
>
>  result = alloc_final( n , free_function , nb_elm*2 , 1  ) ;
                                             ^^^^^^^^^^^^
This doesn't look right: it will force a major GC every time, unless
nb_elm == 0.


>I don't know what is the value of n (n words) : A pointer value
>represent 1 word or 2 ?

A pointer is 1 word, and you must count the pointer to free_function,
so n would be 3.


>How can I store the pointers adr1 and adr2 in value result and how can I
>retrieve them (with Store_field and Field ?) ?

Since the pointer to free_function uses the first field, they would be
at offsets 1 and 2:

        result = alloc_final (3, &free_function, 0, 1);
        Store_field (result, 1, adr1);
        Store_field (result, 2, adr2);

And to use them: "Field (result, 1)" and "Field (result, 2)".

-- Damien