[Dev-C++] Another pointer question (I think its an compiler issue)

[Christian S. <sm...@xs...>]

Thanks for your answer Avik.

I'm now working another question from the book. However I seem to have a
different result than theory would dictate.

Look at and perhaps run the commented source code:

#include <stdio.h>

main ( )
{
  double flt_num, *flt_ptr;

  flt_num = 123,45;

  /* This bit shows (prints) the value of flt_num and then
  it's adress in memory */

  printf ("flt_num = %f.\n",flt_num);
  printf ("The adress of flt_num is %p.\n",&flt_num);

  /* Assigning the pointer to the variable flt_num  */

  flt_ptr = &flt_num;


  /* Setting to value of flt_num via a pointer variable to the
  new value */

  *flt_ptr = 543,21;

  /* Here comes my problem. If I would ask for the value of the pointer.
  Its called flt_ptr btw. In theory it should show the memory address of
  the variable flt_num. But in MSV++ 6 it shows 0.000000 and in DevCPP the
  value of *flt_ptr. Is this a feature or a bug? */

  /* Now I'm priting the value of the pointer to screen */

  printf ("flt_ptr = %f.\n",flt_ptr); /* This should be == to &flt_num  but
it isn't!!*/

  printf ("The adress of flt_ptr is %p.\n",&flt_ptr);

  printf ("*flt_ptr = %f.\n", *flt_ptr);

  return 0;

}

  -----Original Message-----
  From: Avik Ghose [mailto:a_g...@ya...]
  Sent: dinsdag 27 mei 2003 20:52
  To: Christian Schmidt
  Subject: Re: [Dev-C++] Question about pointers (beginner)


  Hi Christian,
  the very statement
                    *ptr_int = 456;
  is malicious. Cause the pointer right now is neither null(except if your
compiler is kind enough to do so) nor it points to any valid address
assigned to your programs run-time memory or the heap.
  As to what your book says, that is completely impossible to happen. If the
program at all runs without any run-time error, the value of *ptr_int will
be 123.

  Christian Schmidt <sm...@xs...> wrote:
    From my book:

    Given x = 123 and ptr_int = &x after that *ptr_int = 456 has been
executed.
    What is the value of x?

    I thought it was 123 as the pointer *ptr_int is a null pointer and can't
    have any value.

    This is how I see it:

    main ( )
    {
    int x, *ptr_int;

    *ptr_int = 456; /*This pointer is a null pointer at this moment right?
*/

    x =123;
    ptr_int = &x; /* As x is just set to 123 and the statement *ptr_int =
456;
    was executed before I would think *ptr_int would be 123 */

    }

    ----------

    But the books says the value of *ptr_int at the end is 456. How come??

    Thanks for your time,

    Christian



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  Thanx and Regards
  Avik Ghose
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