Re: Problem w/lua_pushuserdata

[Edgar Toernig <froese@...>]

Matthias Gall wrote:
> 
> When I push NULL from the C-function like this:
>[...] lua_pushuserdata (m_pLuaState, O); [...]
> get's anything, but never "nil" when it should.

Who said that a pushuserdata(NULL) gives a nil?  You're right that it is
broken in Lua 4.0 - you get a userdata object with some kind of random
pointer but expecting nil...

This patch will fix the bug:

--- src/lstring.c       Sat Apr  7 03:22:54 2001
+++ src/lstring.c       Sat Oct 30 18:49:00 2001
@@ -119,7 +119,7 @@
   ts->nexthash = NULL;
   ts->len = s;
   ts->u.d.tag = 0;
-  ts->u.d.value = (udata == NULL) ? uts+1 : udata;
+  ts->u.d.value = s ? uts+1 : udata;
   L->nblocks += sizestring(s);
  /* insert it on table */
   newentry(L, &L->udt, ts, IntPoint(ts->u.d.value) & (L->udt.size-1));

> lua_pushuserdata _should_ work with a NULL pointer for obvious reasons.
> Any ideas?

It's simply a bug ;-)  But if you expect a nil you have to change your
code too.

Ciao, ET.

PS: Be careful when using userdata objects with the default tag...