Re: Problem passing more than one argument to a Lua function that's inside a table from C++.

[Duncan Cross <duncan.cross@...>]

On Tue, May 12, 2009 at 12:47 AM, Anner J. Bonilla <annerjb@gmail.com> wrote:
> I been trying to get this small application to run since it's a
> testbed for future functionality on my game engine. But i am having
> some trouble trying to get it to call a function inside a lua table
> from C++. More precisely is passing more than one parameter to the lua
> function, return values work fine. also calling a function that's not
> member of a table works flawlessly without any of the argument
> trouble.
>
>
> This is my code without comments and debugging functions.
> inside my main function in c++ i call 4 functions each one returning 1
> if they execute correctly or 0 otherwise.
>
> their name reflects the amount of parameter than they take and test for.
> i have spended about 5 hours today with this trying different
> approaches. so any ideas or suggestions would be greatly appreciated
> my suspicions are that something i am doing with the stack
> manipulation section is wrong. but doubt it because it works fine with
> less than 2 arguments and because when i dump the stack the values
> appear to be what they should be. ie
>
> table
> function
> argument
> argument
>
> after doing the pcall the only thing left on the stack is:
> table
> number
> the number being the return value and i assume the table is the one
> the function was member of.
>
> //main.cpp
> http://pastebin.com/m2f1787b
> //add.lua
> http://pastebin.com/m59b0ead9
>
> Anner
>

Hi Anner,

In add.lua, the test functions use the expression 'not x == nil' to
test that function parameter x is being passed - but in Lua, the "not"
operator binds tighter than "==" (see section 2.5.6 in the manual for
an explicit order of precedence). This means that it gets evaluated as
'((not x) == nil)' rather than '(not (x == nil))', which will always
evaulate to false.

-Duncan