Is it safe to pass int using XtPointer?

When defining a callback proc in Xt (fo开发者_高级运维r example XtTimerCallbackProc), client_data is specified as an XtPointer. Is it safe to pass an int via client_data, rather than an actual pointer, and cast it back inside the procedure?

For example:

void foo(void) {
   ...
   int data = 1;
   XtAppAddTimeout(app_context, 1000, timer_cb, data);
   ...
}

void timer_cb(XtPointer client_data, XtIntervalId *timer)
{
   int my_data = (int) client_data;
   ...
}

Yes; the API uses a pointer because the size of this type is >= the size of an int on almost any computer/compiler combination, so you can use it to pass most things except double simply by casting.

It should be safe, but you should use an integer type that have the same size as a pointer.

The standard C99 type uintptr_t can be used for this purpose.

As per comments point out, int->ptr->int is not guaranteed by the use of this type. It should work more than often, but it is not as per specifications.

The alternative is to pass a pointer. If your app is single threaded, you might just do

static int data; and passs &data. If your app needs to be reentrant, then malloc an int.

As a matter of fact, I don't think the standard support int->ptr->int in any way.