Thread: request for member _mp_size in something not a structure or union

Hello all,

I have a problem with a C program using GMP.
I boiled the issue down to the following:

Code:

#include <stdio.h>
#include <gmp.h>

int main(void) {
  mpz_t foo;
  void *ptrfoo;

  mpz_init(foo);

  if(foo->_mp_size == 0) {
    printf("foo is ZERO\n");
  }
  else {
    printf("foo is not ZERO\n");
  }

  ptrfoo = foo;
  if(((mpz_t *)ptrfoo)->_mp_size == 0) {
    printf("foo is ZERO\n");
  }
  else {
    printf("foo is not ZERO\n");
  }

  return (0);
 }

The error request for member _mp_size in something not a structure or union occurs on the second if statement.
Any idea?
Thanks in advance

Originally Posted by Over_score

The error request for member _mp_size in something not a structure or union occurs on the second if statement. Any idea?

The error:

Code:

test.c:18:30: error: request for member ‘_mp_size’ in something not a structure or union
   if ( ( ( mpz_t * ) ptrfoo )->_mp_size == 0 )
                              ^~

You should write:

Code:

if ( ( * ( mpz_t * ) ptrfoo )->_mp_size == 0 ) ...

Many thanks laserlight and flp1969

Since mpz_t is already a pointer (otherwise foo->_mp_size would not compile), shouldn't it be just ((mpz_t)ptrfoo)->_mp_size?