[GUI] Re: HToolkit binary compatibility

On Sunday, 2003-08-10, 08:58, CEST, Krasimir Angelov wrote:

Hello Wolfgang

--- Wolfgang Jeltsch wrote:

...

at the moment, the different C backends of HToolkit use different types for, e.g., windows handles. In my opinion it would be better if the same type (e.g. char *) would be used with all backends and conversions between the common type (char *) and the native type (e.g., GtkWidget * or HWND) would be made internally.

The HWND type is defined as (void *) in the windef.h header. Is there any hardware platform where different pointer types have different internal representations?

Hello Krasimir, there was a little discussion about this topic some time ago (but I don't remember if it was on the GUI list). I think, the different pointer types will be handled the same on most platforms but I suppose that there is no guarantee for this behaviour. In old times when we used MS-DOS we had severeal memory models (or whatever they were called). In the small model, for example, one had several code segments but only one data segment. In this model, pointers to functions were 32 bit wide (16 bit for the segment address, 16 for the offset address) while pointers to variables were only 16 bit wide (just 16 bit for the offset address)¹). If void * was realized such that function pointers as well as data pointers could be safely cast to void * and back²) then the size of void * had to be at least 32 bit. So void * and char *, for instance, didn't have the same representation.

Krasimir

Wolfgang ¹) This assumes that the stack, the global data and the heap all resided in the data segment. I'm not completely sure if this was the case in the small model. ²) Again, I don't know exactly if this was the case. I used to think so but in the last discussion on this topic someone told me that this is, at least, not enforced by ANSI C.