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Convert from byte ptr to object?

BlitzMax Forums/BlitzMax Programming/Convert from byte ptr to object?

JoshK(Posted 2007) [#1]
Isn't an object just a byte ptr? Is there a way to convert a byte ptr back to an object? This is for Newton.


tonyg(Posted 2007) [#2]
This?


fredborg(Posted 2007) [#3]
Can't you use HandleFromObject and HandleToObject instead of byte ptrs?

Otherwise this dirty (which may fail in a million different cases) trick can be used:
Type TJimmy
	Global list:TList = New TList

	Field great:Int = 1234
	
	Method New()
		list.addlast Self
	EndMethod
	
	Function FromBytePtr:TJimmy(b:Byte Ptr)
		For Local j:TJimmy = EachIn list
			If Byte Ptr(Varptr(j))[0] = b[0]
				Return j
			EndIf
		Next
	EndFunction
EndType

New TJimmy
Local j:TJimmy = New TJimmy
j.great = 1456
Local k:Byte Ptr = Varptr(j)
Local i:TJimmy = TJimmy.FromBytePtr(k)

If i
	Print "Jimmy.great = "+i.great
Else
	Print "Couldn't find Jimmy!"
EndIf



Dreamora(Posted 2007) [#4]
As byte pointer are not managed, there is no clean way to get a Object (managed) from them again.
If you know that only unmanaged data is stored in thought you can memcopy the byte ptr object into a new class object at position 8+ (byte 0-7 are used bm internally for ref count and class ID. Altought with reflection it potentially might be more than 2 ints, so check before depending on this)


Brucey(Posted 2007) [#5]
HandleToObject should work...
myObject = HandleToObject(Int(myBytePtr))

although I've never used it, funnily enough.

Usually, if I have a void* that lets me store user data, I define it in the Extern function like this:
c code...
extern "C" {
   void setMyData(void * data);
   void * getMyData();
}

max code ...
Extern
    Function setMyData(obj:Object)
    Function getMyData:Object()
End Extern


with wxMax though, I've gone one step further, and now interface with BBObject* instead, in my wrappings...
extern "C" {
   void setMyData(BBObject * data);
   BBObject * getMyData();
}

and cast to (void*) or not, where necessary.

...each to their own :-)


fredborg(Posted 2007) [#6]
HandleToObject should work...
But it won't HandleToObject only works in conjunction with HandleFromObject, as it does a lookup in a special hashtable to find the object (at least from my understanding).


Brucey(Posted 2007) [#7]
HandleToObject only works in conjunction with HandleFromObject,

So it does. Just rummaged through the code.
Not sure what use you would have of this really then? What's it for?

Looks like I'll stick to what I know works :-)