Re: Setting the lua_pcall error string on exception (catch block)?

[Tom N Harris <telliamed@...>]

On 04/06/2012 09:29 PM, Eric Wing wrote:
> > It should be enough to just push the error message as part of LUAI_TRY.
> > With C++ it would be something like:
> >
> > #define LUAI_TRY(L,c,a) try { a } \
> >       catch(std::exception e) \
> >           { lua_pushstring(L, e.what()); (c)->status = -1; } \
> >       catch(...) \
> >           { if ((c)->status == 0) (c)->status = -1; }
> >
> > --
> > - tom
> > telliamed@whoopdedo.org
>
> Thanks for responding! I was having trouble with lua_pushstring not
> doing anything for me. I think I finally figured out why.
>
> I needed to change the status code from -1 to either LUA_ERRSYNTAX or
> LUA_ERRRUN. Otherwise the string was getting lost. I found those two
> cases in luaD_seterrorobj where the comment suggests it expects the
> error message on the top.

I see. This was changed in Lua 5.2 which has a default case in seterrorobj.

It occurs to me that using a default catch is a bad idea. That should be 
"catch(lua_longjmp)" and the default will put a generic "unexpected 
error" message on the stack. Or don't handle it so it falls back to the 
host application. You just don't want some random exception to end up in 
seterrorobj which will try to access the top of the stack. That would be 
a bad thing if the exception occurred in "lib.unlock(password)"!

--
- tom
telliamed@whoopdedo.org