RE: Example in Docs: GPOINTER_TO_INT

[Lion Kimbro <lion lithtech com>]

  Dear Ruben,

  It's primarily a convenience;

  Here's the selection out of Pennington
(http://www.andamooka.org/reader.pl?pgid=ggadcha_glib):


--------------------------
There are also many macros unique to glib, such as the portable
gpointer-to-gint and gpointer-to-guint conversions shown in Figure 2.

Most of glib's data structures are designed to store a gpointer. If you want
to store pointers to dynamically allocated objects, this is the right thing.
However, sometimes you want to store a simple list of integers without
having to dynamically allocate them. Though the C standard does not strictly
guarantee it, it is possible to store a gint or guint in a gpointer variable
on the wide range of platforms glib has been ported to; in some cases, an
intermediate cast is required. The macros in Figure 2 abstract the presence
of the cast.

Here's an example:


   gint my_int;
   gpointer my_pointer;
    
   my_int = 5;
   my_pointer = GINT_TO_POINTER(my_int);
   printf("We are storing %d\n", GPOINTER_TO_INT(my_pointer));

 

Be careful, though; these macros allow you to store an integer in a pointer,
but storing a pointer in an integer will not work. To do that portably, you
must store the pointer in a long. (It's undoubtedly a bad idea to do so,
however.)

#include <glib.h>

 

GINT_TO_POINTER(p);

GPOINTER_TO_INT(p);

GUINT_TO_POINTER(p);

GPOINTER_TO_UINT(p);

Figure 2. Macros for storing integers in 
--------------------------

  I suppose you could make a whole structure just to store a pointer, but
it's easier to just use the macro.
  Be sure that ints fit w/in ptrs.

  Take care,
    Lion {:)}=



-----Original Message-----
From: Brooklyn Linux Solutions [mailto:ruben mrbrklyn com]
Sent: Wednesday, May 30, 2001 8:29 PM
To: Daniel V .
Cc: Brooklyn Linux Solutions; gtk-app-devel-list gnome org
Subject: Re: Example in Docs: GPOINTER_TO_INT



> (gint) to_print
>
> The example puts an int in the pointer "slot" instead of a pointer, by
> casting it to the pointer type.  It then retrieves the number by casting
> the pointer back to an int.
>
> Maybe not the best example, but commonly used nonetheless.

I'm sorry  to take  this into a digression, why would we want to 
cast a pointer, which has a memory address stored in it, to an integer?

Ruben

Brooklyn Linux Solutions
http://www.mrbrklyn.com
http://www.brooklynonline.com

1-718-382-5752

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