Re: Determine if function is defined with C API?

[Joey Mukherjee <joey@...>]

On Jul 31, 2008, at 10:12 PM, Patrick J. O'Leary Jr. wrote:

> Ben Kelly wrote:
> > > > > How would I do something like this?  From lua_pcall, I get a  
> > > > > return
> > > > > value of 2 but is this defined somewhere?  Should I just check for
> > > > > that value or is there a preferred constant?
> > >
> > > This requires the function be on the stack and that you know the
> > > index, though.
> > If he's in a position to use pcall on it, it's already on stack and
> > thus using lua_isfunction() is entirely reasonable, no?
> > 	Ben
>
> I took the "return value of 2" to mean lua_pcall returned 2 (which  
> I believe
> is LUA_ERRRUN) so perhaps the function is not on the stack? Simply  
> pushing
> some random things onto the stack (none of which are functions) and  
> then
> calling lua_pcall will give you a return value of 2. It could be the
> function is on the stack but the number of arguments (nargs)  
> supplied to
> lua_pcall is incorrect. I think further details from Joey are needed.

I think what I am doing is pushing random things on the stack and  
hoping they exist.  If they don't, I want to use my default routine.   
If it does exist, and has an error, I want to inform the user.  If  
the function doesn't exist, I don't want the user to know or care.

Here's a snippet of my code:

        lua_getglobal (LState,  
"get_number_of_sensors");           // function to be called
        if (lua_isfunction (LState, 0) == 1) {
            if (lua_pcall (LState, 0, 1, 0) == 0) {

This doesn't work.  Is it because I don't have the right index?  I am  
assuming the lua_getglobal either found the function or if it didn't,  
how would I know?  How do I find the right index to send to  
lua_isfunction?

I feel like I am close, just missing some fundamental piece of  
info!  :-)

Thanks again,
Joey