Name
Type Conversion Macros — portably storing integers in pointer variables.
Library
glib.lib
Synopsis
#include <glib.h>
#define GINT_TO_POINTER (i)
#define GPOINTER_TO_INT (p)
#define GUINT_TO_POINTER (u)
#define GPOINTER_TO_UINT (p)
#define GSIZE_TO_POINTER (s)
#define GPOINTER_TO_SIZE (p)
Detailed Description
Many times GLib, GTK+, and other libraries allow to pass "user data" to a callback, in the form of a void pointer. From time to time, to pass an integer instead of a pointer. Allocate an integer, with something like:
int *ip = g_new (int, 1);
*ip = 42;
This is inconvenient, but annoying to have to free the memory some later time.
Pointers are always at least 32 bits in size (on all platforms GLib intends to support). Thus, at least 32-bit integer values can be stored in a pointer value. Do not do the this as, it is incorrect:
gpointer p;
int i;
p = (void*) 42;
i = (int) p;
Again, that example was not correct, do not copy it. The problem is that on some systems this should be done:
gpointer p;
int i;
p = (void*) (long) 42;
i = (int) (long) p;
So GPOINTER_TO_INT(), GINT_TO_POINTER(), etc. do the right thing on the
current platform.
Warning: DO NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLE IN ANY WAY, SHAPE OR FORM. These macros ONLY allow storing integers in pointers, and only preserve 32 bits of the integer; values outside the range of a 32-bit integer will be mangled.
Details
GINT_TO_POINTER()
#define GINT_TO_POINTER(i) ((gpointer) (i))
Stuffs an integer into a pointer type.
Remember, DO NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLE IN ANY WAY, SHAPE OR FORM. These macros ONLY allow storing integers in pointers, and only preserve 32 bits of the integer; values outside the range of a 32-bit integer will be mangled.
i : |
integer to stuff into a pointer. |
GPOINTER_TO_INT()
#define GPOINTER_TO_INT(p) ((gint) (p))
Extracts an integer from a pointer. The integer must have been stored in the
pointer with GINT_TO_POINTER().
Remember,DO NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLE IN ANY WAY, SHAPE OR FORM. These macros ONLY allow storing integers in pointers, and only preserve 32 bits of the integer; values outside the range of a 32-bit integer will be mangled.
p : |
pointer containing an integer. |
GUINT_TO_POINTER()
Stuffs an unsigned integer into a pointer type.
u : |
unsigned integer to stuff into the pointer. |
GPOINTER_TO_UINT()
#define GPOINTER_TO_UINT(p) ((guint) (p))
Extracts an unsigned integer from a pointer. The
integer must have been stored in the pointer with GUINT_TO_POINTER().
p : |
pointer to extract an unsigned integer from. |
GSIZE_TO_POINTER()
#define GSIZE_TO_POINTER(s) ((gpointer) (gsize) (s))
Stuffs a gsize into a pointer type.
s : |
gsize to stuff into the pointer. |
GPOINTER_TO_SIZE()
#define GPOINTER_TO_SIZE(p) ((gsize) (p))
Extracts a gsize
from a pointer. The gsize must have been stored in the pointer with GSIZE_TO_POINTER().
