Hi, Just checked… contrary to what I believed, strings are passed by copy (not by reference, as ByteArray)… logical for safety but with penalty on performance... so yes, using a ByteArray is the correct way to do it. (Or an external value holder, which is a glorified way for passing a ByteArray, but this probably do not work fine for “char*" because I didn’t preview it :P)
Esteban > On 13 Apr 2016, at 05:24, Nicolai Hess <nicolaih...@gmail.com> wrote: > > > > 2016-04-11 15:10 GMT+02:00 Esteban Lorenzano <esteba...@gmail.com > <mailto:esteba...@gmail.com>>: > > > On 11 Apr 2016, at 06:24, Thibault Raffaillac <thibault.raffail...@inria.fr > > <mailto:thibault.raffail...@inria.fr>> wrote: > > > >>> 1) Declare a class variable > >>> > >>> MyClass class>>initialize > >>> INT_PTR := FFIExternalValueHolder ofType: ?int?. > >> > >> as a larger explanation, this will create an anonymous subclass to keep > >> ?int? > >> values, than later you can use as a type in your function call. Some > >> people > >> would call this obscure, but is a good way of solving this problem (I > >> adopted it from old NB). > >> If you want to have a named class instead an anonymous class, you can just > >> subclass FFIExternalValueHolder: > >> > >> FFIExternalValueHolder subclass: #MyIntPtr > >> > >> and then implement typeDecl class method > >> > >> MyIntPtr class>>typeDecl > >> ^ ?int' > >> > >> and this will work as the anonymous class > > > > The second option is definitely what I want. > > Personally my option would be to put my types in a class pool and use them, > not to extend… > but option is there so you can choose what you want :) > > > I am trying to expose a function returning several ints, as in > > SDL2>>mouseStateX: y: (excluding the possibility to return a Point). > > However I would rather not define my own int holder, can't we have generic > > holders to rely on? > > I will not add for the moment that predefined types value holders… We would > need to add one for each type we support to be consistent, and document it, > and add tests. > And btw… you do have a generic holder… is just that you need to refine it to > what you want :) > You could always use a ByteArray and took values later (some functions in > Athens do it like that). The advantage of this approach (using plain > ByteArrays) is that you do not need to change function signature at the cost > of needing to do manually what the value holder does for you. > > Hi Esteban, > > is this the way it should be done for Strings ? > For example, old NBOpenGL had this Windows method to get the Window Title: > > getWindowText: hWnd buffer: lpString bufferSize: nMaxCount > <primitive: #primitiveNativeCall module: #NativeBoostPlugin> > > ^self nbCall: #(int GetWindowTextA(HWND hWnd, char* lpString, int > nMaxCount)) > module: #user32 > > called as: > > getWindowText > | len str | > str := ByteString new: 1000. > len := self getWindowText: self buffer: str bufferSize: 1000. > ^ str first: len. > > > When I just modify the ffiCall to > > getWindowText: hWnd buffer: lpString bufferSize: nMaxCount > > ^self ffiCall: #(int GetWindowTextA(HWND hWnd, char* lpString, int > nMaxCount)) module: #user32 > > I get just an empty String. > > But If I call it with: > > | len str | > str := ByteArray new: 1000. > len := self getWindowText: self buffer: str bufferSize: 1000. > ^ String fromByteArray: (str first: len). > > I get the real string text. Is this the way to go? > > > > > My advise is that you go with what you need, we can consider add predefined > value holders later. > > Esteban > > > > > Thibault > >
