Q32893: Difference between Huge Pointers

Article: Q32893
Product(s): See article
Version(s): 4.00 5.00 5.10 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 19-JUL-1988

Problem:
   I have two huge pointers that are more than 32K apart. However,
whenever I take the difference between them, I get an incorrect
answer. I am using the following code:

char huge *ptr1 = (char huge *)0xa0000000;
char huge *ptr2 = (char huge *)0xb0000000;
main()
{
  long k;
  k = ptr2-ptr1;
  printf("difference is %ld\n",k);
}

Response:
   This problem occurs because the difference between two pointers is
considered to be an integer quantity. The arithmetic that is done on
the huge pointers is 32-bit arithmetic, but the result is truncated to
an integer, then promoted back to a long value with a sign extension.
   To retain the original long value returned by the huge-pointer
arithmetic, cast the result of the subtraction to a long value. For
example, you will get the expected results with the following code:

char huge *ptr1 = (char huge *)0xa0000000;
char huge *ptr2 = (char huge *)0xb0000000;
main()
{
  long k;
  k = (long)(ptr2-ptr1); /* cast the integer to a long */
  printf("difference is %lp\n",k);
}

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