For convenience, GMP provides a parallel series of initialize-and-set functions
which initialize the output and then store the value there. These functions’
names have the form mpz_init_set…
Here is an example of using one:
{
mpz_t pie;
mpz_init_set_str (pie, "3141592653589793238462643383279502884", 10);
…
mpz_sub (pie, …);
…
mpz_clear (pie);
}
Once the integer has been initialized by any of the mpz_init_set…
functions, it can be used as the source or destination operand for the ordinary
integer functions. Don’t use an initialize-and-set function on a variable
already initialized!
void mpz_init_set (mpz_t rop, const mpz_t op) ¶void mpz_init_set_ui (mpz_t rop, unsigned long int op) ¶void mpz_init_set_si (mpz_t rop, signed long int op) ¶void mpz_init_set_d (mpz_t rop, double op) ¶Initialize rop with limb space and set the initial numeric value from op.
int mpz_init_set_str (mpz_t rop, const char *str, int base) ¶Initialize rop and set its value like mpz_set_str (see its
documentation above for details).
If the string is a correct base base number, the function returns 0;
if an error occurs it returns −1. rop is initialized even if
an error occurs. (I.e., you have to call mpz_clear for it.)