RE: Callback problem
- Posted by Andy Serpa <ac at onehorseshy.com> Oct 12, 2002
- 380 views
kbochert at copper.net wrote: > > >From: Andy Serpa <renegade at earthling.net> > >To: EUforum <EUforum at topica.com> > >Date: 10/11/02 10:29:11 PM > >Subject: RE: Wrapping C - Callback troubles > > > Bernie Ryan wrote: > > > > Andy Serpa wrote: > > > Here's another problem. I'm making the Berkeley DB wrapper which > allows > > > for certain callback functions to be used. One particular one > I'm > > > trying to set up is supposed to be a void function. The callback > works > > > (my function is called), but when it returns a value (any value) > it > > > crashes. (Callback functions are required to return something.) > > >But that's not the problem. Setting the callback function is no > >problem, and my Euphoria function is being called with the correct > >args. > >The problem is when my function exits (returns a value) the whole > >thing > >crashes with an exception. I was just wondering is that because it > >is a > >supposed to be void function? (It seems like I should be able to > >return > >anything in that case, but maybe it wants me to return nothing?) > >Anybody know anything about that? > > This sounds like the cdecl-stdcall problem. Many packages that come > from the unix world expect the callback function to be cdecl rather > than the windows standard stdcall. If the callback is of the wrong > variety, the stack gets messed up. > > I modified Bach to accept cdecl callbacks -- under Euphoria I think > the easiest option is to modify the calling convention in the source > and re-compile the package. > > There probably is a way to fix it by poking assembly. > See the "Matt Lewis Help!" post -- I'm doing all this in cdecl now. Still doesn't work on the void function and then there is also that odd thing with the extra parameter in the other function. I don't know a thing about ASM so I couldn't possibly tell if maybe the fptr.e stuff isn't quite right -- hopefully Matt or someone else can. I am at the limits of my knowledge...