Re: how to tell near from far pointers

Is this what you need?

char  far df[10];

char  dn[10];

//return 1 if far pointer can be downcasted to a near pointer
int  safe_downcast (void  far *pf,void  **pn)
{
   union  {
     struct  {
       void  *n;
       unsigned  int  h;
     } s;
     char  far *f;
   } u;
   u.f = pf;
   if  (u.s.h == 0xffff)
   {
    *pn = u.s.n;
    return  1;
   }
   return  0;
}


int  main ()
{
   char  far *pf;
   char  *pn;
   int  ok;

   printf ("Size of far pointer is %d\nSize of near pointer is %d\n\n",sizeof(pf),sizeof(pn));
   df[0] = 0x55;
   dn[0] = 0xaa;

   pf = df;
   ok = safe_downcast (pf, &pn);
   printf ("Far data: pf is 0x%08lx\nContent of *pf is 0x%02x\nsafe_downcast says 
%d\n\n", pf, *pf, ok);

   pf = dn;
   ok = safe_downcast (pf, &pn);
   printf ("Near data: pf is 0x%08lx\nContent of *pf is 0x%02x\nsafe_downcast says 
%d\n", pf, *pf, ok);
   printf ("pn is 0x%04x\nContent of *pn is 0x%02x\n", pn, *pn);
}



Mircea Neacsu
M: 514-591-0329
E: [email protected]

On 10/6/2016 6:57 AM, [email protected] [rabbit-semi] wrote:
>
> Does anybody know what is the standard way to tell if a pointer can be 
> safely casted to near?
>
> Here is a sample program:
>
>
> #include "xbee/platform.h"
>
> void my_dump(void far *address)
>
> {
>
>   const char far *data = address;
>
> printf("Address %" PRIpFAR, data);
>
>   printf(" contains: 0x%02" PRIX8 ".\n", data[0]);
>
> }
>
> char far f[64];
>
> char n[64];
>
> void main ()
>
> {
>
>   f[0] = 0x00;
>
>   n[0] = 0x01;
>
>   my_dump(f);
>
>   my_dump(n);
>
> }
>
> The output looks like this:
>
> Address 107FC0 contains: 0x00.
>
> Address FFFFB372 contains: 0x01.
>
> The "my_dump" function should be able to recognize a near pointer for 
> proper formatting.
>
> By the way ( address == (void far *)(void *)address ) is true when 
> address is near, but it also throws a warning ("Explicit cast from 
> pointer-to-far to pointer-to-near.")
>
> Thank you.
>