File: gawk.info,  Node: API Ownership of MPFR and GMP Values,  Next: Registration Functions,  Prev: Constructor Functions,  Up: Extension API Description

17.4.5 Managing MPFR and GMP Values
-----------------------------------

MPFR and GMP values are different from string values, where you can
"take ownership" of the value simply by assigning pointers.  For
example:

     char *p = gawk_malloc(42);      p "owns" the memory
     char *q = p;
     p = NULL;                       now q "owns" it

   MPFR and GMP objects are indeed allocated on the stack or
dynamically, but the MPFR and GMP libraries treat these objects as
values, the same way that you would pass an 'int' or a 'double' by
value.  There is no way to "transfer ownership" of MPFR and GMP objects.

   The final results of an MPFR or GMP calculation should be passed back
to 'gawk', by value, as you would a string or a 'double'.  'gawk' will
take care of freeing the storage.

   Thus, code in an extension should look like this:

     mpz_t part1, part2, answer;             declare local values

     mpz_set_si(part1, 21);                  do some computations
     mpz_set_si(part2, 21);
     mpz_add(answer, part1, part2);
     ...
     /* assume that result is a parameter of type (awk_value_t *). */
     make_number_mpz(answer, & result);      set it with final GMP value

     mpz_clear(part1);                       release intermediate values
     mpz_clear(part2);

     return result;                          value in 'answer' managed by 'gawk'